NewBeetle.org Forums banner

1 - 20 of 24 Posts

·
Registered
Joined
·
78 Posts
Discussion Starter #1
I have a 2002 Beetle with the 2.0 engine. I recently got 2 codes - PO036 and PO141. Since the sensor was old I naturally replaced it. 2 days later I got the PO141 code again. Could it be a defective sensor or what?
 

·
Registered
Joined
·
78 Posts
Discussion Starter #5
oxygen sensor problems

jfoj,

thanks for your response. It seems somebody attached a thread to my thread.

I have 3.5 volts going to my o2 heater. I know it's supposed to be 12 so where do I go from here?
 

·
Registered
Joined
·
3,690 Posts
jfoj,

thanks for your response. It seems somebody attached a thread to my thread.

I have 3.5 volts going to my o2 heater. I know it's supposed to be 12 so where do I go from here?
Be careful as the O2 sensors probably do not have power all the time so you may be monitoring a supervisory Voltage.

Not sure how long the O2 heaters are on at cold start up, but assume at least 3-5 minutes on cold start?
 

·
Registered
Joined
·
78 Posts
Discussion Starter #9
oxygen sensor problem

jfoj
I turned the key on engine off at cold startup. Then I took a reading at the plug for the rear o2 sensor and I had the 3.5 volts. This should be 12 so the heater is turned on. I still have the po141 code. My wiring diagram shows one feed to the heater coming from the ecu and the other from the ignition coil plug.
 

·
Registered
Joined
·
3,690 Posts
Your better at reading the wiring diagrams than I am.

Every time I look at a VW diagram, I have to relearn how to read them!!

My electronic Bentley shows that there are 2 wires for the O2 sensor heaters.

Brown with White Strip coming from the ECM and Blue with Red Strip coming from somewhere in the engine bay that I have not been able to located yet. Connection 87a in the wiring harness.

Which wire has power?

Assume the Blue with Red stripe?
 

·
Registered
Joined
·
78 Posts
Discussion Starter #11
I think the blue/red wire is positive. The other wire goes to fuse 43 (10 amp). The other side of fuse 43 comes from the fuel pump relay. It means when the fuel pump relay is energized it turns on the o2 heater. The front o2 sensor has a completely different power supply.

I just do not understand the low voltage reading.
 

·
Registered
Joined
·
3,690 Posts
I will have to check my diagram again, but it looked like both O2 sensors are fed from the same +12 source and the ECU would actually control the ground side?

In any event, it sound like a bad connection assuming you are not just seeing some form of supervisory Voltage, which is usually 5 Volts anyway.
 

·
Registered
Joined
·
2,231 Posts
It looks like the same power source (fuse 43 and the 87a connector) is used for the MAF sensor. You could check the voltage at pin 2 of the MAF to see if the low voltage exists there too. If low there, check the voltage at the fuse 43 connector as well. Could be an issue with the fuel pump relay.
 

·
Registered
Joined
·
78 Posts
Discussion Starter #14
If this is a supervisory voltage then another sensor would control when the voltage changes. Do you know which on it is?

As far as the power going to both sensors It would seem I would have the same problem with the upstream o2 sensor but I don't.
 

·
Registered
Joined
·
78 Posts
Discussion Starter #15
I had someone else tell me today to check the MAF sensor. I will try that next.

Does anyone know of a talented VW mechanic in SE New Hampshire?
 

·
Registered
Joined
·
3,690 Posts
Why are we checking the MAF sensor for an O2 sensor heater fault??

Maybe I am missing something here. Sounds like someone that has NO IDEA how engine fuel management systems work?

DO NOT REPLACE THE MAF SENSOR AT THIS TIME. Need more info about what is going on.
 

·
Registered
Joined
·
78 Posts
Discussion Starter #17
I won't replace the MAF. I just wanted to check the voltage. My first instinct was a ground problem. I wonder if I can tap the ground wire from the front sensor for the rear. I know the front is okay.
 

·
Registered
Joined
·
3,690 Posts
Chances are if the MAF Voltage was low, you would have a MAF code of some sort?

You can use a test light to easily check grounds by connecting the test light clip to positive 12 Volts, then use the probe end to verify ground wires.

Do not try to make supplemental grounds from other sensors, if you make a mistake, you could end up with a problem. Get a ground from a ground point if you plan on doing this, but check the ground path with a test light first as it puts a small load on the circuit and the brightness of the light will tell you more than a meter will.
 

·
Registered
Joined
·
2,231 Posts
According to the schematics the O2 sensors don't use a direct ground connection. The grounding for the heating element is done through the ECU. If the ECU has a bad ground connection then it could cause the low heating element voltage. The heating element for the PCV valve uses the same ground as the ECU so you can use that to check the ECU ground. Disconnect the line at the PCV valve and check the voltage on the brown/red wire relative to the battery negative terminal with the key on/engine off. It should be very close to 0.

In my earlier post I described how to check the supply voltage to the O2 sensors.

When you measured the 3.5 volts on the O2 sensor earlier where did you have the meter probes?
 

·
Registered
Joined
·
78 Posts
Discussion Starter #20
I measured the voltage across the 2 white wires for the heater. As far as the PCV heater it was disconnected when I bought the car. I wonder what the reason for that was.
 
1 - 20 of 24 Posts
Top