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Discussion Starter · #1 ·
My daughter is having issues with her 98 Beetle stalling. Check engine light was on, scanning showed coolant temp sensor and o2 sensor bank 1 sensor 1 (inbound sensor).
I replaced the coolant temp sensor last weekend, this didn't fix the issue, so she went to the shop and had the o2 sensor replaced this morning. I made sure I bought the Bosch O2 sensor since I'd read other o2 sensors could cause issues.

The car is still stalling. It seems to be idling too low. Driving it's fine, it's only when the clutch is pressed when coming to a stop or the car is in neutral it stalls.

The check engine light hasn't come back on. This leads me to believe the issues that were throwing the codes were fixed but something else is still wrong. I'm just not sure how to proceed at this point. Any help would be appreciated.
 

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The first thing to check is the throttle body adaption. If the battery has been disconnected for a length of time the ECU won't adjust the idle speed automatically until this is done. You can do this by switching the ignition switch to "run" without starting the engine. Wait 30 seconds and then switch off.

The coolant sensor code could have been caused by an old thermostat. They generally last about 5 years before they won't allow the engine to get to proper operating temperature. These cars are prone to bad temperature sensors, but the usual symptom is the blue "cold" light coming on intermittently when the engine is warm.
 

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Discussion Starter · #3 ·
Thank you for the quick response.

I sent a text to my daughter about turning the car to run for 30 sec then switching it off. ( I gave her a link to my post too but I know she'll never read it ). Hopefully it will be that simple.

I remember seeing a blue light when I was driving the car, I thought it was just the window washer fluid level so I didn't pay it much attention. If resetting the ECU doesn't fix the issue I'll plan on changing the thermostat next. It may be next weekend till I can get to a heated garage to change it. Ohio weather doesn't lend itself to working outside much in the winter.

At least I have something else to try that won't be too expensive. I was thinking MAF, but that was a worst case scenario. Thanks again.
 

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wrong

Thank you for the quick response.

I sent a text to my daughter about turning the car to run for 30 sec then switching it off. ( I gave her a link to my post too but I know she'll never read it ). Hopefully it will be that simple.

I remember seeing a blue light when I was driving the car, I thought it was just the window washer fluid level so I didn't pay it much attention. If resetting the ECU doesn't fix the issue I'll plan on changing the thermostat next. It may be next weekend till I can get to a heated garage to change it. Ohio weather doesn't lend itself to working outside much in the winter.

At least I have something else to try that won't be too expensive. I was thinking MAF, but that was a worst case scenario. Thanks again.
Sorry but I think you did that wrong, it's not to the RUN position it's to the ON position without starting the car and then turn back to the off position. Also if somebody mixed the wrong coolant in the system the thermostat tends to develop rust and does not seal properly and also causes the coolant temperature to be outside the working perimeter. These cars are very finicky about their operating temperature and proper coolant. Good luck
 

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A few things.

O2 sensor will not cause the car to stall, MAF likely will not either, but it could.

Suggest you get a OBDII scan tool on the car that can read and display Freeze Frame and Live/Real Time data.

For $30 or under this can be done with a smartphone, iPhone or Android. You need an App for $5-$15 and an interface for $15 or less.

Also the temperature sensor was not your problem, car needs a thermostat. This should not cause the car to stall, but may cause it to run poorly, get poor fuel mileage and have excessive carbon build up.

Read the links below in my signature.

First thing I would suggest it to check the fuel pressure regulator vacuum hose on the top of the engine to make sure it is not broken.

Chances are the engine has a vacuum leak/crankcase air leak.

Probably the O2 sensor code was not for a bad O2 sensor but a code indicating the O2 sensor was beyond the typical range of operation or at edge of measurement because of a vacuum leak.

Need Long Term Fuel Trim info and engine coolant temp info from a OBD tool that supports Live Data and any Freeze Frame data.

Could also be a failing fuel pump, but will leave this to later in the discussion.
 

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Discussion Starter · #6 ·
Thanks everyone. I told my daughter to try putting her car in the on position and run position each for 30 seconds and shut it off between. Neither worked.

The car may have a vacuum leak. I'll have to check.

The big thing though, is the thermostat. Thanks for suggesting this. I ask my daughter if she had any heat (last time I drove her car was 2 weeks ago to fix her brakes and it was warm outside). She said no. My guess is that it's stuck open since there's fluid. I'll change the thermostat when I get a chance, probably Monday or weekend after next. Garage availability is the only thing keeping it from being sooner.

I normally use my uncle's scanner, but I didn't realize they were so inexpensive. I'll pick one up in the next couple days and hopefully will be able to provide the fuel trim and engine coolant temp info.
 

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Discussion Starter · #7 ·
Changed the thermostat, checked for vacuum leaks. Car has heat now, and the blue light went off. Checking the thermostat, it was slow opening and closing, so I'm glad that was mentioned.

Car is still stalling, but now only when it's revved up and rpms drop quickly. Easing in/out keeps it from stalling. My daughter was able to drive it without it stalling, I didn't have the same luck, but I drive it so little, I rev it up more since I'm not 100% sure where the clutch pedal releases.

My uncle suggested the MAF or Throttle Positioning Sensor may be causing this and we're going to clean those out Friday morning.

I did pick up a scan tool. I got the Autel AL319. I wasn't sure what everything meant to get fuel trim data. After changing the thermostat, the car was EC was around 158 F (70c). The rest of the data was a mystery to me. I'll check the fuel trim data if someone can tell me which numbers to copy.
 

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The blue coolant light comes on when the car is cold. When the car is cold, you're supposed to drive it gently, so I try to keep the car under 3k rpm until the blue light goes out. When the blue light goes out, it should be up to normal operating temperature.
 

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The Autel AL319 will display Live/Real Time data.

You better recheck the engine coolant temperature. Should be 205F/96C after about the first 10 minutes of DRIVING. My guess is you checked the temp when the car was not fully warmed up.

Blue coolant light should go out at about 135F/57C or just about of mile of driving if there are no stops. Blue light going out is not normal operating temperate, it is far from it. With a good thermostat the engine should hit normal operating temp within about 10 minutes.

Find what is called Long Term Fuel Trim (LTFT) and check this at warm idle. Should be between 0% and +2.5%. Anything above + 2.5% I would be concerned and start looking for vacuum leaks.

Forget about cleaning the MAF and the throttle position sensor is not likely the problem. I would check for vacuum leaks and investigate if the idle control valve can easily cleaned.

Also check the vacuum hose from the fuel pressure regulator on top of the engine is not broken, common problem on these engines.

Also consider fuel filter replacement, they are cheap and often overlooked.
 

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Discussion Starter · #10 ·
I replaced the fuel filter about a year ago when I first got the car. I didn't think it would go bad that quick, but if it starts looking like the fuel pump, I'll replace the fuel filter again first.

The temp reading was done while the car was in idle, after about 15 min. It hovered around 157/158F. It didn't act like it wanted to get any hotter, but the fan never kicked on, so it wasn't at a max temperature and the heat in the car was good. We never got any air bubbles, but I'm not sure if they were to be expected or not with that setup.

The ODB II connector is loose, and wants to wiggle around when connecting. I haven't looked into what it will take to make this more stable but hopefully I'll be able to do that Friday morning.

When checking for vacuum leaks, my uncle sprayed something ( I think WD40 ) around listening for a drop in the RPMs, there wasn't any. The car was only idling around 650 RPMs though and you could smell the fuel. That's why he suggested taking off the hose going to the air filter and cleaning everything we could.

I hate to admit it, but I don't know a lot of what I'm looking at when I look at the engine. You would think 4 years as an Army Mechanic, and working in a garage for about a year after would leave me better equipped for this. Mostly I just feel lost without AllData. I'll find a picture of the fuel pressure regulator, and it's location before Friday and make sure I check that vacuum line since you've mentioned it twice already. I doubt I'll be able to talk my uncle out of cleaning everything, but it's a small price to pay for a heated garage.

I suppose I should mention I replaced the plugs, wires and ignition pack about 6 months ago, since it hasn't come up.

Thank you for your patience and continued help.
 

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I replaced the fuel filter about a year ago when I first got the car. I didn't think it would go bad that quick, but if it starts looking like the fuel pump, I'll replace the fuel filter again first.

The temp reading was done while the car was in idle, after about 15 min. It hovered around 157/158F. It didn't act like it wanted to get any hotter, but the fan never kicked on, so it wasn't at a max temperature and the heat in the car was good. We never got any air bubbles, but I'm not sure if they were to be expected or not with that setup.

The ODB II connector is loose, and wants to wiggle around when connecting. I haven't looked into what it will take to make this more stable but hopefully I'll be able to do that Friday morning.

When checking for vacuum leaks, my uncle sprayed something ( I think WD40 ) around listening for a drop in the RPMs, there wasn't any. The car was only idling around 650 RPMs though and you could smell the fuel. That's why he suggested taking off the hose going to the air filter and cleaning everything we could.

I hate to admit it, but I don't know a lot of what I'm looking at when I look at the engine. You would think 4 years as an Army Mechanic, and working in a garage for about a year after would leave me better equipped for this. Mostly I just feel lost without AllData. I'll find a picture of the fuel pressure regulator, and it's location before Friday and make sure I check that vacuum line since you've mentioned it twice already. I doubt I'll be able to talk my uncle out of cleaning everything, but it's a small price to pay for a heated garage.

I suppose I should mention I replaced the plugs, wires and ignition pack about 6 months ago, since it hasn't come up.

Thank you for your patience and continued help.
I would verify the the engine temperature again. You may have a bad coolant sensor if you are reading 158F after 15 minutes. Engine should be 205F within about 10 minutes of DRIVING. See if the coolant sensor is a green top sensor, the originals were black and had issues.

For the coolant sensor location and what it looks like see these -

Auto part Automotive fuel system Automotive engine part Brass Fuel pump

Auto part Fuel line Engine Hose Pipe

For the Fuel Pressure Regulator location and hose, see this - http://www.eanswer.com/vw-volkswagen/43gm7-replace-fuel-pressure-regulator-2001-vw.html
 

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Discussion Starter · #12 ·
I've replaced the coolant temp sensor...supposedly. There were 2 in the hose and I read the 2nd one was the right one, closest to the back/engine. Her car takes the blue one though, not the green one.

Ok, the 2nd thing you showed, Fuel Pressure Regulator...will that swing freely if it's broke? It looks like this thing that was down below the air filter hose just hanging. I wasn't able to determine where it went, so I assumed a clip had just broke and left it. From the picture it looks like there's a clear hole it should go into so it may be something different but the one side of what I saw looked like that. I'll try to do a long term fuel trim when I get off work...and see if I can find the fuel regulator, hopefully attached.
 

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BTW, the fans will not come on until the temps get around 210-215F.

As for the Fuel Pressure Regulator, the FPR will not be loose, otherwise there will be a massive fuel leak, but the vacuum hose can break and fall down on the top of the engine.

Not sure if the 2.0l uses the green or blue top CTS, but you need to figure out if the engine temp is 205F after about 10 min.
 

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Discussion Starter · #14 ·
Ok, Fuel Pressure Regulator - I called my uncle before leaving work to ask him about it. He knew what it was, said it had 2 vacuum lines running into it, and he checked both last night, they're ok. Still don't know what the loose thing is.

I was able to get the temp up to about 140F in 10 min, so still really low. It's snowing here, when I started it was 50F.

Long Term Fuel Trim stayed at 0.0%. Left me wondering if it was working, though you said this was an acceptable range. I made screen shots of the other settings with my phone...they didn't turn out too clear, and the one with RPMs had a flash over the number, but it was idling around 850RPMs.

There were 2 codes...it was cleared after I worked on it so new. One was for coolant temp sensor, other was for low RPMs.

DTC_CNT 2
FUELSYS1 CL - But it switched to OL-Drive when I Revved the engine and let it drop. Not sure if this is supposed to stay closed or not.
LOAD PCT(%) 3.9
ECT 140
SHRTFT1(%) -25.0
LONGFT1(%) 0.0
RPM 850
VSS(rpm) 0
SPARKADV(*) 10.0
IAT(F) 62
MAF(lb/s) 0.01
TP(%) 4.3
AIR STAT OFF
O2B1S1(V) 0.835

Let me know if I need to get any other readings, the rest were too blurry to read without redoing.
 

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Ok, Fuel Pressure Regulator - I called my uncle before leaving work to ask him about it. He knew what it was, said it had 2 vacuum lines running into it, and he checked both last night, they're ok. Still don't know what the loose thing is.

I was able to get the temp up to about 140F in 10 min, so still really low. It's snowing here, when I started it was 50F.

Long Term Fuel Trim stayed at 0.0%. Left me wondering if it was working, though you said this was an acceptable range. I made screen shots of the other settings with my phone...they didn't turn out too clear, and the one with RPMs had a flash over the number, but it was idling around 850RPMs.

There were 2 codes...it was cleared after I worked on it so new. One was for coolant temp sensor, other was for low RPMs.

DTC_CNT 2
FUELSYS1 CL - But it switched to OL-Drive when I Revved the engine and let it drop. Not sure if this is supposed to stay closed or not.
LOAD PCT(%) 3.9
ECT 140
SHRTFT1(%) -25.0
LONGFT1(%) 0.0
RPM 850
VSS(rpm) 0
SPARKADV(*) 10.0
IAT(F) 62
MAF(lb/s) 0.01
TP(%) 4.3
AIR STAT OFF
O2B1S1(V) 0.835

Let me know if I need to get any other readings, the rest were too blurry to read without redoing.
OK, so we have some issues.

1. ECT (Engine Coolant Temperature) as they say "No Bueno".
Regardless of the outside temp, the Blue engine temp light should go out in about 1.5 miles or driving or less. This light typically goes out around 135-137F engine coolant temp.

Document how many miles it takes to get the Blue temp light to turn out.

2. ECT (Engine Coolant Temperature) 140F after 10 minutes, does it ever go any higher? If not, thermostat or coolant sensor is a problem. Since you JUST put a new thermostat in, hope you did not mix up and install old one back in the engine, you may want to consider replacing the engine coolant sensor?? I guess it is an issue of what is cheaper and easier. If you replace the engine coolant sensor and the temp is still the same, then you get the replace the thermostat again. Also keep in mind, just because the thermostat is new does not mean it will work properly.

3. The first line of data states DTC CNT 2, this means you currently have 2 DTC or Diagnostic Trouble Codes or "codes", assume the CEL is on? What are these codes and provide the Freeze Frame data associated with these codes.

4. STFT is -25%? Is this static, is it dancing around? Can you mentally average this? -25% STFT means something is in BAD shape. RARELY do the fuel trims operate at a negative value and if so for only very short periods and only values under -5%. Flag this!!!!!

5. LTFT at 0%, does this move? It should, if it is not moving, again something is very wrong, maybe due to the engine coolant temp being or THINKING is is so low? Flag this!!!!

Everything else looks in line and does not jump off the page.

We have to get the ECT sorted out, either the engine is running too cold or the sensor is reporting the engine is running too cold. This can cause a lot of issue.

STUPID VW will almost never trigger an engine temperature problem, not sure who wrote their ECU software.

See attached graph of a car with a good thermostat, driving at highway speed for almost 40 minutes in close to freezing temps. Not the graph as not from cold start, but usually the initial temperature rise is typically pretty linear and on a flat line rising.
 

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Discussion Starter · #16 ·
The two codes were

P0506 - RPMs lower than expected
P0116 - Engine Coolant Temperature Circuit Range/Performance Problem

They both came on when the car stalled. I checked for Freeze Data and it said none saved.

Posting a video on YouTube of the car when revved with STFT. It moves, I did this originally to show it going into open state, but got lucky it included this data too. 98 Beetle Engine when reved - YouTube

I'm sure I put the new thermostat in. We put the old one in a vice when we pulled it and heated it up with a propane torch to make sure it was an issue. The old one opened and closed but very slowly for both so was probably bad.

I haven't been driving the car around to check the temperature. Both times it was idling for about 10-15 minutes, this may be why it's not as hot as expected. The ECTS is still throwing codes, even after it was replaced, so I may have gotten a bad one. I'll order one or two for Friday morning. Probably two because there are two in the radiator hose, and I can't be sure someone didn't switch them since if I remember right both had wires going to them.
 

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Before you spend money on parts, can't you just drive the car for 4-5 miles and see if the engine temp goes above 140F?

I will try and see how long my 1.8t takes to warm up if I have time this morning.

Take a picture of what you think the coolant sensor is, I believe there is only 1 in the area, but I have not looked closely at a 2.0l. The sensor should be a 4 wire sensor, because it has the wiring for the blue cold light in it. It should be either the blue to green top sensor depending on the connector type you have. Blue is a square type connector, green top if it was replaced has a rounded connector on one side.

I saw the YouTube video, it is somewhat normal for the engine to come out of closed loop when the engine winds down as this is usually fuel cut off mode.

Also your fuel trim displayed in the video was STFT which is always rapidly moving if this are operating correctly. Typically STFT will run in the range of about -5% to +15% and usually be within a window of about 10%.
 

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Discussion Starter · #18 ·
I've attached a picture of the ECTS, hardest part about getting the picture was having my daughter stay home long enough for me to take it. I labeled everything too so there's no confusion.

I'm not sure what the first plug is. I didn't realize it was only 2 prongs instead of 4 till I popped the connector this morning.

I'll be working on the car again in about 6 hours, so if you see this before then, I'll try to get the first sensor if you know what it is. When I was reading about replacing the ECTS before, it said the first one was just a plug, but I'm not sure why a plug would have wires going to it.
 

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The 2-pin sensor is the A/C thermal cutout, so only cars with A/C will have one. The 4-pin one is the one the ECU uses.
 

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Discussion Starter · #20 ·
Thanks red99. I would have never guessed the A/C was related to the water temp. I called and it's only a $12 part so I'll replace it just to be on the safe side.
jfoj, my daughter's out driving the car now. I'll take a temp reading when she gets back. Hopefully the readings will be a little higher. If not, I'll replace the ECTS this afternoon.
 
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