Lambda sensor issues!

[pizzaboy150]

Hi Chaps,

I have had an on going issue now for the last few months with the car never stalling but having a rough idle and loss of power and misfiring. The problem seems a bit intermittent and only seems to occur when the car is hot.

I scanned the car and got back P0537 which indicated lambda, fuel pump, fuel pressure regulator, charcoal filter, faulty injector.

now the P0537 code comes on all the time but every now and again I get a P0525 error which is purely Lambda sensor issue.

I have checked the fuel pump and pressure with a gauge off ebay and that seems fine.

I checked the wiring for the 2 heater wire and 1 signal wire that seem to go straight to the ecu under the wiper cover and the resistance is measuring less than 6 ohms which seems good.

BUT the 4th wire does not go to the ECU is runs past it then back down the right side of the bulkhead towards the battery.

I couldn't see to much at were it ends up but I measured the resistance in the wire from the battery to the end of sensor cable and measured 20K ohms of resistance along that cable. I am assuming that is the power supply for the lambda heaters? I also cannot see if it runs through anything or whether 20K would indicate a faulty wire.

I was thinking about running a new wire from the battery terminal to the lambda sensor but not sure if the lambda sensor can handle 12Volts and am a bit worried about killing the ECU.

So my next test was on the output of the sensor its self after I had the car running for about 20 minutes I tested the voltage across the output of the lambda and it was averaging around 1.5 volts jumping between 1 and 2 volts, whilst all the information I have seen indicate on various forums that it should average around 0.45 volts ish for the correct mixture?.

also the sensor is my second new one first sensor i bought was a universal sensor then I bought the proper sensor from audi same issues.

It driving me nuts!

[NickPicks]

I thought that a lambda sensor should be constantly switching voltage as it switches from rich to lean. I can't find my logged file, but I seem to recall that it outputs around 0.2v for lean, and 1v for rich. If you use datalogging in vcds, then you should be able to plot a graph of it bouncing up and down at tickover.

Edit: just found my thread a few years ago where I posted the logged data from measuring blocks on lambda voltage.

[pizzaboy150]

My voltage is switching but between 1v and 2v, also I believe the higher the voltage the more oxygen is being detected and the leaner the mixture.

Unfortunately I do not have access to data logging and anoyingly my car does not seem to be OBDII so had to buy a cheap VAG code reader.

[Alan02]

Dont forget to check other factors that will affect the actual readings you get at the Lambda. Yes, it adjusts mixture settings but that is based on whats coming out of the cylinders. If there is a problem on the injector / intake system this will influence the lambda reading.

[pizzaboy150]

Problem solved! There was a rupture on a gasket in between the upper and lower intake housing allowing air through. I put some thread tape on it cleared the errors and the problem has not come back and new gaskets in the post.

Its interesting to see how a tiny fault can cause all kinds of problems you really have to think hard about these error codes.

Thanks though!

[Alan02]

Pleased you found the problem....and it was "upstream of the suspect!"

[Keithuk]

EOBD II Error Code: P0537

Fault Location:
AC Evaporator Temperature Sensor - Circuit Low

Possible Cause:
Wiring/Connector(s) short to earth.
Fuse(s).
AC evaporator temperature sensor.
Engine Control Module (ECM).


EOBD II Error Code: P0525

Fault Location:
Cruise Control System, Actuator Control - Circuit Range/Performance

Possible Cause:
Wiring/Connector(s).
Cruise control actuator.


As taken from my EOBD II Error Codes