[waterworld]

Happy new year, everyone!

Last Monday(12/24) night I was driving my roommate to IAD with a real high speed... As we were approaching the airport (5 mins left), the EPC light went on for around 10 seconds and simultaneously, I felt the car lost some power but it recovered after EPC went off. At this time MIL was still off.

After arriving the airport, I turned the car off and waited for 20 mins and then I drove back home. About 5 mins after I left the airport, MIL went on, but (as I remember) EPC was off. I then stopped for a while, and have no choice but keep going on. Everything was fine during the trip back home. (Only MIL was on all the time.)

Later I learned from this forum (thanks guys) and bought a VAG-COM. It got two codes:

[URL="http://wiki.ross-tech.com/wiki/index.php/16705/P0321/000801"]16705 - Engine Speed Sensor (G28): Implausible Signal[/URL]
        P0321 - 35-10 - - - Intermittent
[URL="http://wiki.ross-tech.com/wiki/index.php/17704/P1296/004758"]17704 - Error in Mapped Cooling System[/URL]
        P1296 - 35-10 - - - Intermittent

My bug is 2001 2.0L Gas with 95k on it.

I've searched around for the Engine Speed Sensor problem, but answers seem to have a wide coverage... for the problem related to cooling system, I don't know whether it's a new or old problem... back 5 month ago I didn't notice the coolant level until the coolant light turn red (I added the coolant immediately after that)

Another supplementary is that, in March this year, the EPC light had been on for several minutes when I was starting a trip on an interstate. I stopped the car, turned it off, and then restarted, EPC didn't show up again, and it didn't trigger MIL. Everything went smooth, until this Christmas IAD trip.

Thanks for help

UPDATES:

• Thermostat was bad (early open; soft failure), replaced in Jan 2013.
• Started to have P0118 [Engine Coolant Temp Sensor (G62): Signal too High, Intermittent] since Feb 2013. Changed the old black coolant temp sensor to the new green sensor in June 2013.

 

[jfoj]

So I will take a stab at this.

P1296 - I would suspect a bad thermostat. Only way to know for sure is to monitor the coolant temp. Engine likely should run normally around 200-205F. These stats usually fail low and open too early. Code stats as intermittent, this is pretty typical of a failed stat, they only occasionally trigger stat codes.

P0321 - Impossible speed means the value did not agree with other data the ECM was seeing, probably engine RPM did not agree with vehicle speed?? Also states the issue is intermittent.

Not sure what to tell you here, I think???? this is the crank sensor, but not 100% sure.

 

[waterworld]

Hi jfoj, thanks for your quick reply

Regarding to the potential failure of thermostat, I ran the software and found the coolant temp to be normal: it's 83C within a possible range 80--110C. (figure, see here) So can I conclude the engine coolant thermostat is fine, but it went wrong occasionally?

I'm actually thinking about the keyword "intermittent." Is there a possibility that my car mainly works fine, but since I didn't clear the code for at least 9 months, the rare events add up as if they were "intermittent"?

Today I cleared the code for the first time, the MIL hasn't come up yet after a 3-mile test drive. Do you think I should wait for some more time to see how it goes, or I should send the car to a VW dealer? (as a student, I really don't want to do so)

 

[jfoj]

You did the correct thing on clearing the codes. You really want to document the date & mileage when you get codes, clear them and then monitor the situation and if and when codes come back and which ones show up first. In order to properly play the game, if and when the CEL comes back on you want to immediately read the code(s), BUT do not clear them, continue to drive the car and keep monitoring to see if other codes appear and note in which order.

As for your 3 mile test drive. If you measured you coolant temp in the 3 mile drive, it may not have come up and stabilized in just 3 miles, BUT, I would see where the temp ends up after 5 miles. Also if VAGCOM/VCDS can log temperature, I would log the temp and see how it behaves.

Also if you only drove the car for 3 miles after clearing codes, your Emission Readiness Monitors have not even cleared yet. You will need AT LEAST 2 cold starts and close 30 miles driving with at least about 1/2 of the driving at highway speed before the Readiness Monitors clear. Also if your coolant temp is too low, which I think it is, you may take longer for the Readiness Monitors to clear?

I think your stat is bad. I just replaced the stat in my 1.8t. In the entire 10 years of ownership, I did get the stat code CEL only 1 time, however, I never changed the stat. Just recently I started to monitor the "real time" data as I did not have a scan tool that would read real time data previously and I found the temps too low, however, I did not have a CEL for the stat. My temps were running as low as 170-180F.

I replaced the stat and BANG, engine is almost always at 200-205F (93-96C). You CANNOT rely on the ECM to monitor and reliable tell you when the stat has gone bad. The window is too wide otherwise you will likely have false CEL or a CEL that triggers too often. Trust me, your stat is bad, your engine temp should be much higher. I am not sure where the engine temp data you found was from, but his is a generic window. If you check the stat temp for your car is likely 185F, this is the stat temp for my car. Why does the engine temp on my car show 200-205F, this is due to where the temp is monitored, in the cylinder head water jacket. My BMW M5 actually has the temp sender on the top of the thermostat housing, so it monitors the temp in a VERY different location and it does in fact monitor the actual temp that the thermostat operates at.

These stats almost always fail open/open too soon when they fail. You cannot rely on the blue coolant light in these car either. They turn too early and usually the coolant light will turn off about the same time window even with a bad stat. This who thermostat issue frustrates me to NO END as this community and others, tend to always want to change the coolant temp sensor. Usually because it is MUCH easier to replace and typically cheaper on some cars, when the likelyhood of a simple thermister failing is VERY low. The 1.8t engines apparently had some issues with the coolant sender, however, the problem with it was mainly with cold start and ambient temps off by maybe at most 10F, probably less.

It is critical you change your stat today, no, but do it soon, engines that run too cold run too rich, get worse fuel economy and have problems getting the oil up to the proper temp to "cook" out excess moisture, condensation and fuel. You will also have accelerated engine wear as well. Note sure if the stat is located in the same place as the 1.8t, behind the alternator?? I did my stat without taking the alternator off, not so easy, but with some 1/4" drive wobble extension and/or a 1/4" universal joint it is possible to get at the lower bolt. It was not that hard to change, just get the stat and do the job. Probably $20 in parts. Just get a pan to capture the coolant and a paint filter to strain the coolant to reuse. Also if you need to add coolant, get it from the dealer. Also use distilled water if you need to cut it. While the stat is out, feel around the back of the water pump for broken plastic vanes. If your car has the original timing belt and water pump, put this on your Springtime list of things to do. Blauparts has very complete kits, even has antifreeze and thermostat plus more for about $250. You may want to buy the kit and use the stat and antifreeze from the kit?

Trust me, if your engine is not consistently in the 200F range, your stat IS bad. It drives me CRAZY how many cars are driven for years with bad stats as people just are convinced a single stat code is an error or just a temp sender. I was burned by this as well. This is what happens when your car does not have a real temp gauge!

As for your Engine Speed Sensor - Implausible, I might wait and see what happens? I know this is not a good idea as you may think you can be left hanging, however, your problem appears to be intermittent. I would not take the car to the stealership as their guess will be about a good as yours. You spent your money on your VAGCOM/VCDS so you would not have to visit the stealership. Use your tool and your head and take the $90-$125 per hour you would spend at the dealer and put it toward parts at wholesale prices.

It appears the car may be trying to go into limp mode?? Usually shutting the engine off and then restarting will likely clear the issue, even if still coasting.

I am thinking if it was my car, I would be guessing at either MAF or crank sensor? I would replace the MAF sensor first as these are more prone to degradation over time and are easy to change. If you change your MAF sensor, keep the old one. Also do not ebay a MAF sensor, get a quality Bosch unit from a reliable source. I have seen a lot of problems lately with ebay/cheap MAF's causing lean conditions during cruise. It appears there are either counterfeits, bad quality units or bad applications out there.

 

[waterworld]

Hi, jfoj. Thank you very much for your detailed reply!

For the stat part, I'm now going to drive the car around and use vagcom to record the temperature in real-time.

If I can change the stat by myself, according to your description, I don't need a ramp, right? (I actually don't have one)
If I cannot change it by myself, is it a good idea to have the mechanic change it for me?

And here

Blauparts has very complete kits, even has antifreeze and thermostat plus more for about $250

Is this "2" a typo? I had a big tank a coolant from dealer which was around $30, and stat for $20 as you said? So I guess the total cost should be around $50?

The Emission Readiness Monitors take time to clear, so I will wait and see.

For the Engine Speed Sensor part, I'm also going to follow your words--wait and see.

Thank you, indeed!

 

[jfoj]

And here
Is this "2" a typo? I had a big tank a coolant from dealer which was around $30, and stat for $20 as you said? So I guess the total cost should be around $50?

Sorry I was not clear on this point, the $250 was for a complete water pump/timing belt kit. It is actually much cheaper for the 2.0L @ $149. I think this is for your car?

Vw Beetle Timing Belt - Vw Beetle Timing Belt Kit - 2.0L Basic

I just mentioned this as if your car has the original water pump and timing belt, this should be on your Spring to do list.

As for needing ramps for the stat, might be helpful. Autozone has Rhino Ramps, plastic ramps in stock at most stores for about $45. They are lightweight and work well.

Or you could possibly roll up on a curb on one side of the car. Main issue is getting to the coolant petcock, but you may be able to just catch as much as you can from the stat housing?

I think the trick it the under carriage cover it in the way?

Mechanic can easily replace the stat, just be careful who and where you go, not the stealership!

 

[IndyTom]

Happy new year, everyone!

Last Monday(12/24) night I was driving my roommate to IAD with a real high speed... As we were approaching the airport (5 mins left), the EPC light went on for around 10 seconds and simultaneously, I felt the car lost some power but it recovered after EPC went off. At this time MIL was still off.

After arriving the airport, I turned the car off and waited for 20 mins and then I drove back home. About 5 mins after I left the airport, MIL went on, but (as I remember) EPC was off. I then stopped for a while, and have no choice but keep going on. Everything was fine during the trip back home. (Only MIL was on all the time.)

Later I learned from this forum (thanks guys) and bought a VAG-COM. It got two codes:

[URL="http://wiki.ross-tech.com/wiki/index.php/16705/P0321/000801"]16705 - Engine Speed Sensor (G28): Implausible Signal[/URL]
        P0321 - 35-10 - - - Intermittent
[URL="http://wiki.ross-tech.com/wiki/index.php/17704/P1296/004758"]17704 - Error in Mapped Cooling System[/URL]
        P1296 - 35-10 - - - Intermittent

My bug is 2001 2.0L Gas with 95k on it.

I've searched around for the Engine Speed Sensor problem, but answers seem to have a wide coverage... for the problem related to cooling system, I don't know whether it's a new or old problem... back 5 month ago I didn't notice the coolant level until the coolant light turn red (I added the coolant immediately after that)

Another supplementary is that, in March this year, the EPC light had been on for several minutes when I was starting a trip on an interstate. I stopped the car, turned it off, and then restarted, EPC didn't show up again, and it didn't trigger MIL. Everything went smooth, until this Christmas IAD trip.

Thanks for help

You more than likely need a new Crankshaft Positioning Sensor also known as the Rpm or Impulse/Speed Sensor. Very common for them to wear out after reaching a certain age and mileage. I carry a spare just in case

Volkswagen New Beetle 2.0 > Search > Crankshaft Sensor > ES#252763 Crankshaft Position Sensor - 06A906433C

The second code more than likely is your Coolant Temp Sensor especially if you still have the original "Black" Sensor installed. The 2.0's came with either the square or the half square/half round sensors so make sure to get the correct one for your car.

OEM / Performance Parts for Audi, BMW, Mercedes Benz, Mini, Porsche & Volkswagen - ECS Tuning

I would try the coolant sensor first before trying to swap the Thermostat since that is a bit more difficult to do. If your CEL comes back after clearing it than you can always go ahead and change the thermostat which is a bit of a pain to do.

Good Luck!

 

[jfoj]

Trust me, if your engine is not consistently in the 200F range, your stat IS bad. It drives me CRAZY how many cars are driven for years with bad stats as people just are convinced a single stat code is an error or just a temp sender.

Drink all the Koolaide you want regarding the temp senders, they usually were just off by a few degrees at ambient temps and caused cold start issues.

These thermostat last maybe 4 years at tops before they start soft failing. I have seen some not last 2 years.

Your engine should run close to 200F consistently.

 

[IndyTom]

Drink all the Koolaide you want regarding the temp senders, they usually were just off by a few degrees at ambient temps and caused cold start issues.

These thermostat last maybe 4 years at tops before they start soft failing. I have seen some not last 2 years.

Your engine should run close to 200F consistently.

Okay, fess up, you are really a secret Stant Thermostat Salesman trying to jump start the poor economy by selling a Million Thermostats this year to earn your trip to Shanghai and a golden Needle

Sure Thermostats go bad especially the cheap aftermarket ones but I have also seen them last well over 10 years. My 2001 Audi TT 1.8 never had the Thermostat changed and always was spot on. I keep an eye on the actual temp via a Scangauge II gauge which gives me readouts on several vital engine stats.

If he still has the original Black or in case of some older 2.0's a blue coolant sensor than I would bet the farm that it is the Coolant sensor and not the Thermostat. Those older Sensors had a knack for failure and should be replaced with the new "Green" type sensors regardless.

If that doesn't do the trick there is always time to get messy and change that Thermostat. Why not start with the easier of the two options first?

 

[waterworld]

Thanks Tom! Thanks jfoj!

I've obtained real-time data of my car. Don't know whether they are normal...

3 trips in total, please see attachment. (You may want to change the file extensions from TXT into CSV so that they can be opened with a spreadsheet software.)

I drove on roads has speed limits 35, 45. I didn't go to interstate. The Emission Readiness Monitors (8 sensors) all passed eventually.

When I was driving, I noticed that the coolant temp increases when I stops at red lights, and decreases when I drive. The initial temp was only 52C/126F, the highest was 91C/196F.
(I also noticed the data has a column "Intake Temp", which is around 26C/79F. What is this about?)

 

[jfoj]

Looks like your thermostat is bad, a soft fail as I call them. I did not graph this out, but looked over the raw data. You can see that the temps did finally hit about 90C, however, the seemed to drop back to the 70's at cruise at times. If the 2.0 is like the 1.8t, with a 185F stat you should have coolant temps where the sensor pick up at the output of the cylinder head of 200-205 consistently.

Here is the drill, really simple. Check the coolant temp after sitting all night to see if the coolant temp is very close to the ambient temp. If it is higher than the ambient by more than about 5F, then change your coolant sensor, but this will have very little bearing, if any, on how your upper temperature stabilizes once the car is fully warmed up. It is likely your ambient temp will almost always be higher than the coolant temp if the car is outside and gets any solar load if you happen to use the outside temp indicator next to the clock as a reference.

BUT, even if the coolant sensor is off, you should see a plateau in engine temp near the 200F mark and stay within about +/-5F in these Winter outside temps. Summer months, you may see the temps creep a bit higher until the fans kick in.

A typical failure mode of the thermostat (especially German car stats) is they open early, extend the warm up period, if they ever get up to temp, they do not hold the temp, then the temp will wander and drop especially while driving on the freeway once the RPM's are up and the airflow over the radiator is constant. Basically the temperature is always wandering. With a soft failed stat, you will likely be able to get very close to the proper operating temp at idle, but once you start to drive, the temp will avalanche fairly quick. Many of these newer stats are designed to fail open and everyone expects the failures to be digital. The either never warm up or totally overheat. This is not really the case these days. Also even if the stat fails hard open, depending on the ambient temp, the engine will warm up to some value that may or may not trigger any OBD codes. ODB codes unfortunately are way to broad, they are designed this was as to not cry wolf all the time.

For example, I get into disputes ALL the time regarding fuel trims. My threshold is about +/-3%. I do not like seeing the fuel trims ever hit +3%, if they do, I say there is a problem. However, the ECU will not typically trigger any codes for fuel mixture until close to 10%. There are plenty of cars running around on the road that have fuel trims consistently above 3% with not CEL coming on!

To IndyTom, let me tell you this, and this is the first time I have publicly stated this as I usually keep my cards very close. I have over 35 years experience working on cars, have 2 Associate Degrees in Automotive Technology, a Bachelors in Engineering, was a Certified Master Automotive Technician at the age of 16, was a state safety and emissions inspector, have worked for major automotive manufactures in the Field Service Group and have 7 Automotive Troubleshooting Wins to include 1st place at the National level. I deal with cars on a daily basis and I am not some DIY guy that just screws around with a few cars that I happen to have my driveway, although I do this as well. This does not even include any of my computer, networking and communication circuit background. So I believe I am just a bit capable of understanding what typically goes on in the "real" world.

So you can jump up and down all day about how the problem is the coolant sensor that is a stupid PTC or NTC thermistor, you are not the first to do this, it seems not only here, but on many other forums people get their teeth into a specific issue and just do not let it die and the myth becomes gospel. It is a really simple part that rarely fails, if anything is to go wrong it is more likely with the internal solder joints than the actual thermistor itself.

I glanced over the raw data and the issue appears very clear. If I have time I will graph out the CSV files the OP provided, but once the engine reaches its max temp, it should hold within about 5F of this temp without much effort.

I see thermostats go soft ALL the time, this is nothing new. Just because your one car has a 10 year old thermostat that you "think" is fine, lucky you. The majority of the cars out here cannot keep a thermostat more than about 4-5 yeas at tops and even then I would change the stat as a PM measure because 99% of the time you only figure out the stat is not working is during the dead of Winter when most of us to not have access to a fully heated garage and have unlimited time to address the problem at our leisure. Many of the cars are driving around with soft thermostats, running too cold, using too much fuel and not properly heating up the oil to cook off all the moisture, water vapor and fuel in the crankcase. This then leads to premature oil breakdown, crankcase deposit build up and a host of other issue even with automatic transmission.

I am sure the OP can make his own mind up as to what he things is needed on his car, he has decent data and once he knows what is supposed to be "normal" I think he will see the light!

Nuff said.

Happy New Year!

 

[waterworld]

Thank you, jfoj!

Your explanation is very clear. With the help of Google I cleared up some jargon (as I'm new to cars), and I now understand the situation: the thermostat is bad. (It's not a digital device so that bad means it does not work properly as designed. Or, let us call it inferior.) The bad thermostat opens more than enough when engine is still cold so that excessive coolant circulated to cool the engine / prevent the engine from reaching the working temperature, say, 200F. This leads to low oil efficiency and etc. as jfoj described.

I'm going to change the thermostat and temp sensor at a mechanic. I will also seek the possibility to change the timing belt and water pump simultaneously, if they hadn't been changed at 60k (when they supposed to be changed according to the manual, please correct me if I'm wrong).

I have done research on how to change the thermostat on Beetle 2.0L Gas. This a good(?) Youtube video with step-by-step explanation. I'd love to do the DIY and actually have alreaday opened the engine cover this morning, but I do have some other constaints that made me to throw the work to the mechanic.

jfoj suggested the BLAU timing belt kit. I think it's a good deal with a thermostat as a present. I also looked into other aftermarket brands, and found the ECS timing belt kit may also be an alternate.

jfoj, thank you for your great effort I owe you too much time on this post! I really appreciate your help, both to me and, to other future readers of this post.

 

[jfoj]

I think you have a pretty good plan of attack. If you want and need to replace the thermostat now, they are only about $20 with the O-ring as I recall?

The reason I mentioned the timing belt/water pump was your mileage and I know many of the timing belt kits come with the thermostat, O-ring and many also include a new thermostat housing as they are plastic and can deteriorate with heat over time.

The Blauparts kit appears to be a better deal as you get antifreeze and the thermostat housing as well for only about $16 more than the ECS system even when on sale. Your call as to what you think needs to be done.

Regardless of what VW recommends, I kind of prefer 60k increments on timing belts. Looks like you have had yours replaced previously so this is may not as critical as getting the engine to the proper operating temp.

As for the engine speed plausibility code, I would keep an eye out for this. The plausibility codes are a bit squirrely in my opinion. They are really assumptions based upon multiple points of data. The issue is "we" do not know how the ECM/ECU is coded and programmed to make these assumptions.

So for example does the engine speed plausibility only monitor the engine crank sensor?? I do not think so?? Because if the crank sensor was seeing the engine tuning as say 2500 RPM, then it sees what it thinks as the engine turning as say 10,000 RPM for an instant, then I would expect that the engine would have stalled and you would have had some form of crank sensor code. The crank sensor is used for the spark timing and monitoring for misfires and such. So you likely would have had a slew of codes of this type of problem occurred.

What I think happens with a lot of the plausibility codes is the ECM/ECU looks at a lot of inputs. In this case for engine speed I would assume that crank sensor, cam sensor(s), throttle position sensor, gas pedal position sensor, MAF sensor, vehicle speed sensor and possibly the coolant sensor, would likely be monitored. As you can somewhat offset and make assumptions based upon the data that is available.

If the engine really revs up, the crank sensor, cam sensor and and MAF all likely are expected to see a similar change in values, meaning the crank and cam sensor pulses should increase equally and for all intended purposed the MAF should also see an increase in airflow and you would expect to see the throttle position and gas pedal position change accordingly. If your are driving down the road, the ECM/ECU could also look at vehicle speed as well.

Again all the plausibility codes are based upon assumptions, if you are driving at 60 MPH and then in an instant the ECM/ECU sees the vehicle speed at 80 MPH with no change in engine RPM, throttle angle, gas pedal position, or other sensors, then this condition is somewhat implausible.

Same holds true if you are driving along and all the sudden the camshaft sensor detects an increase in pluses, however the crankshaft sensors stays consistent, then this can be considered an implausible condition, likely in this case you would have a cam sensor code triggered?

I am inclined to rule out the crank sensor as your main problem as you did not mention the engine stalling, but going into what appears to have been a limp mode. If the crank sensor even starts to trip up, usually this is almost and instant stall as the ignition and fuel injection is really controlled by the crank sensor. Additionally if the crank sensor signal disappeared even for a short period, many times the fuel pump is shut down, some fuel pumps are controlled by crank signals, some are controlled by oil pressure detection, some may be controlled by a combination of both. This is performed as a safety feature to kill the fuel pump in case of an accident where the ignition is not turned off and the engine is not running.

So the point I am making is now you will really need to watch and monitor what is going on with your car relative to the plausibility codes. You need to perform a code check say once every few weeks, even if you do not have an active CEL, there are pending codes that can show up before a CEL is ever triggered. If the CEL pops on, you really need to try and read the codes immediately, but do not clear them, run with the light on for at least a week and check the codes every day and see if you get any additional codes and also note if the CEL clears on its own. Remember to log the date and mileage of all codes as sometimes the logged info will start to draw a clearer picture once you get more data over time. Sometimes depending on what the code is and if it is intermittent, the ECM/ECM will clear the CEL on its own without external intervention and you may miss data that could be useful.

Good luck and I would like to hear and see how the new thermostat reacts once you have it installed.

 

[waterworld]

Good news!

Hi, jfoj. I came back from the mechanic, and everything regarding to the temperature control problem was set! The labor cost is $135. As you can see from the figure, the coolant temp after changing the thermostat is now within the working region, say, around 93C/200F!

I had also shown the upper plot to the mechanic and he also agreed that the thermostat is highly likely to be inferior. I added, "if possible, please also change the temp sensor." But he said if after changing the thermostat the problem persists, then change the temp sensor later. Fortunately, the temp sensor needs not to be changed. The old thermostat was inferior as it opens too early, exactly as you estimated!

I will now keep an eye on the Engine Speed Sensor part. Each time I read your writing, I understand more.

Thank you very much for help, jfoj !

 

[jfoj]

waterworld,

Thanks for follow up. As you can see once the engine really warms up how stable the temperature stays vs with the bad stat it never gets up to temp and then keeps diving low and is very unstable.

Your situation is not that uncommon, however, too many have been drinking the coolant sensor Koolaid and it is not just here with the VW's, I have seen this on MANY forums. Although there were coolant sensor issues with the early VW sensors, they were not as big of an issue as some made them out to be in my opinion. Most of the problem sensors had a fixed offset that more often than not caused cold start issues as the sensor was registering too high. Again, you can just compare your ambient temps to the cold engine and make sure the engine is not warmer than ambient.

You will see improved fuel economy, performance and your crankcase will really appreciate what you have done for your temperature. One of the bigger side effects of a cold engine is the oil does not heat up fast and hot enough to really cook off condensation, water vapor and unburned fuel. This leads to quick sludge and other build up in the crank case. Hot oil is a much better cleaner than cold oil.

I personally think at lot of the 1.8t sludge/carbon flaking in the oil was also a side effect of cool running engines along with the lack of synthetic oil.

Now you need to start watching your O2 sensors and fuel trims with your graphing. Most O2 sensors should baseline at 0.45 Volts when cold. You will likely be able to graph your O2 sensors and find a lazy sensor. You may want to put a new O2 sensor on your Spring to do list give the age and mileage of your car. I buy all my Bosch O2 sensors from Amazon for around $50-$60 and have had no issues with them. I always use Bosch sensors with the proper connectors. Bosch really invented the O2 sensor and they have the system down very well.

 

[waterworld]

Hi jfoj,

Thanks for informing me to check O2 sensors. I've studied what's the function of O2 sensor in a car [1][2], but it turned out my VAG-COM software is a trial version so that I cannot pull out the information from Group 032... I will try it later, will be recently. Thank you, again!

 

[waterworld]

Hi jfoj,

As you predicted, I ran some tests and suspect that the pre-cat O2 sensor is lazy! It always has a voltage above 1 volt, say, 1.4 volt! However, apparently the lambda factor was kept well around 1, so I'm confused.

I've plotted data (see Trip One & Trip Two) into 6 figures, please see the attached PDF file. I hope the plots are clear.

And here are my questions,

1. Were the fuel trims (additive & multiplicative) correct? Apparently they are not changing with time, -1% and +7% for additive and multiplicative, respectively.
2. The voltage of pre-cat O2 sensor was always above 1 volt, I think should jump back and forth between 0.2 and 0.9 volts. Does it imply that the O2 sensor is bad? If yes, why did the lambda factor keep steady around 1 which implies a fairly good control on the concentration of gas and air.
3. Was the catalytic converter operating in an acceptable temp range? According it the measurement, mine was 350C--750C / 660F—1400F.

Thank you very much

 

[jfoj]

I am not sure what is going on with the O2 sensor.

I will try to find a decent graph so you can see what a typical sensor will look like.

At baseline before the O2 sensor becomes active, the Voltage should be 0.45 Volt. From there the Voltage should swing from about 0.1 - 0.9 Volts. I have seen occasionally when the air pump is on that the O2 sensor Voltage may actually get very close to 0 Volts for a VERY short period of time.

Fuel trims at +7% are a bit scary, means the engine or at least the O2 sensor thinks the fuel mixture is lean.

I might be inclined to just say hit Amazon.com, get a Bosch O2 sensor and replace the front sensor. $50 from Amazon, I just put this in my '03 1.8t - Bosch 17014 Oxygen Sensor, OE Type Fitment : Amazon.com : Automotive NOTE: This may not be the correct sensor for your car, I just wanted to give you an idea of what they cost and the application function on Amazon.

O2 sensors are consumable items and on turbo cars, I feel they take more of a beating and should be replaced without fail by 75k miles. Don't worry about the rear O2 sensor at this point.

As for the catalytic converter temps, they look decent, cannot recall, but O2 sensors need to be around 600F to function can converters typically run around 1200F as I recall. Not sure where and how the temp is measured, maybe rear O2??

 

[waterworld]

Is this a good figure?

According to my memory, immediately after I started my car, the front O2 sensor had a voltage 1.4... In comparison, the rear O2 sensor was around 0.45.

And I will get the Bosch O2 now. Thanks!

 

[jfoj]

That's more like what you would expect to see.

There could be an issue with the software not reading and interpreting the data correctly, however, I would doubt this is the case with VAGCOM/VCDS?

Could be a wiring short of some soft. It is almost impossible for an O2 sensor to put out more than 1 Volt by nature of the design. You might try to just unplug the sensor and see what registers on the tool, it should be 0V?

Not mine, but a decent graph that should be easy to read.




Not mine, but a decent graph. Note the scale is off on the O2 sensor Voltage, but this shows a good and lazy O2 sensor together.