o2 sensor low voltage problem.

Poula

Hi

I have a 151 Skoda Fabia 1.0 With reoccuring fault code p0137. Bank 1 sensor 2 low voltage. It happens when Im driving and then drop the accelerator to change gear. Immediately the voltage drops of to 0v from the sensor then climbs again when I push the accelerator again. Ive been watching it on the Torque app on my phone whilst driving.
I have replaced the sensor, Checked the wiring and voltages with a multimeter. Ive checked the current and resistance of the heater coil. Checked the exhaust for leaks. Starting to run out of Ideas. Anyone else have experience of this?

scannerd

As far as i know, P0137 means the O2 oxygen sensor's voltage remained low for longer than 2 minutes, having a low voltage coming off the accelerator would be normal as mixture goes lean at that point.

I would suggest you need log the data over a longer time period to see if / when the longer drop out is happening.

Also sensor 2 should be after your cat so are you sure you changed / measuring the right one?

Poula

Hi.

It was the sensor below the Cat I changed. Ive been monitoring it over the weekend and from what I can tell Im driving along normally and the sensor is behaving normally. When i come off the accelerator the voltage immediately drops to 0. as soon as I start on the accelerator again the voltage climbs to normal again. What I have noticed however is that if IM driving along and drop the accelerator and press in the clutch also.. so I'm coasting.. the voltage only falls to 0.2v and not zero. I can sometimes get several hours before the check engine light comes on and i have to reset it. This has me flummoxed.

scannerd

"When i come off the accelerator the voltage immediately drops to 0. as soon as I start on the accelerator again the voltage climbs to normal again. What I have noticed however is that if IM driving along and drop the accelerator and press in the clutch also.. so I'm coasting.. the voltage only falls to 0.2v and not zero."


This sounds like normal operation to me, can you get freeze frame data with your scanner? records snapshot of key data at time of the fault.


What are you fuel trim values?

Poula

Hi Just had the car out for a spin and took some snapshots of 02 sensor voltages and fuel trim values whilst driving.

The first one is normal driving.

The second and third are when ive dropped off the accelerator.

scannerd

looking at the first one,

trims look ok as does sensor 1, but you would expect sensor 2 to be moving up and down, just less then sensor 1, it looks like its at a fixed voltage all the time - should not be.

Was the replacement OEM?

I think i would bench test it on a gas stove / torch to see it is responding correctly

Poula

Hi.

yep it was an OEM part from Skoda

A few more pics before I dive in under the car.. The sensor is a pig to get out..

The first is accelerating

The second is Dropping off the accelerator

The third is Back on the accelerator again

And the fourth is Back off the accelerator.

Hope these better images might throw some light on things.

scannerd

I know, they a pig to get at. Good that is OEM, but Still looks odd, should be oscillating more like sensor 1, and not going down fully to 0

Your error is voltage too low over 2 min.

You can see it's going to 0 when senor 1 will not go below 0.1 - I think that's the issue.

If the senor behaves the same on a bench test (fully hot) then I think its suspect - a good working sensor should not go fully to 0 as far as i know - did you keep the old one could test it?


Or reverse the sensor plugs (if they will reach - don't drive around), if you then see "sensor 2" going to 0 then wiring or ecu suspect - but very unlikely.

Poula

Cheers for the help. I think I still have the old sensor. I'll see what's what with that first and then I might just whip the new one out and bench test it. It's definitely starting to look like the sensor is suspect.

John.G

Poula wrote: »

Hi.

yep it was an OEM part from Skoda

A few more pics before I dive in under the car.. The sensor is a pig to get out..

The first is accelerating

The second is Dropping off the accelerator

The third is Back on the accelerator again

And the fourth is Back off the accelerator.

Hope these better images might throw some light on things.

What readings are you getting at idle with engine at normal temperature?.
Both Sensor1 & Sensor2 seem to be flat lining in your charts.
In your fourth trend both are flat lining after you "come off the accelerator" if you leave your leg off, do the readings become normal again? especially sensor1.
In all the VAG cars (VW) that I had/have had Sensor 1 always flip/flops rapidly between 0.2V and 0.8V, the fuel trim causes this (in all cars) to keep the mixture at stoichiometric conditions. Sensor 2 AFAIK monitors the performance of the Cat and is not the same type, on a 2005 Polo sensor1 flip/flops rapidly between 0.2V/0.8V and sensor2 stays fairly steady at 0.85V. On a 2008 Passat Sensor1 goes 0.2/0.8V rapidly and sensor2 stays very steady at 0.45V.

Have you checked for air leaks, it could just possibly be a malfunctioning PCV valve causing problems, can't think of anything else just now.

Lucifer

I would not be concerned about the 0v when you take your foot off the accelerator, it is the ECU turning off the injectors and is normal and the ecu expects this reading. The low voltage code you are getting is more likely to be an air leak causing a lower than expected voltage . Check freeze frame of the condition when the code was stored to see engine speed and load to get an idea if the problem is at idle or under load.

Poula

Okey dokey.. So in the end the problem turned out to be a bad replacement sensor. I brought it back to Skoda and they gave me a replacement. all good now.. Thanks for the help guys. :)