djtalon

So i had a check engine come on and got a code P0154 ( o2 sensor CHK No activity. Bank 2 sensor 1)

I replaced the drivers side front sensor and go for ride, shut car off go for a ride again and it comes back.

I replaced the pass front sensor just in case and same thing happens and it comes back. When i watch it on the actron reader when i clear the code and go for a ride it is pending, shut engine down and restart after 5 minute ride it turns check engine light on and code goes from pending to default.

Please help i cannot figure it out.

ezveedub

No activity doesn't mean its a dead O2 sensor. It means the ECM is not seeing any change for a period of time from the O2 sensor, which could be an extreme lean or rich condition. If you have VAG-COM, you need to check the ECM measurement value block 33 for live fuel trim adjustments. If its rich or lean, the percentage will jump up above 10% + or - when the ECM memory is cleared.

djtalon

makes sense, so what would cause extreme lean or rich condition? i have a ross-tech comming on friday.


thanks

djtalon

also i forgot, every once in a while i would get a multiple misfire code or a cylinder 4 misfire

ezveedub

Check the spark and coil on cylinder 4. If anything, swap the coil with another cylinder and the spark with another also. If the misfire moves with the ignition parts, then thats the issue. If it stays with with cylinder 4, then either the injector is bad (possible wiring to injector also) or the cylinder has a mechanical issue (low compression or wiped out cam lobe and bucket).

As for fuel mixture, MVB (measurement value block) 33 has four fields of data. Fields 1 & 3 are the idle mixture percentages. Fields 2 & 4 are the off idle or part throttle mixture percentages. Field 1 & 2 is Bank 1 mixtures and field 3 & 4 are Bank 2 mixtures. For your issue, your looking for a percentage value in field 3 of MVB 33. If all the other fields have values close to zero, but field 3 is stuck at zero value, you most likely have broken signal wire in the harness from the O2 sensor to the ECM, since you've replaced the O2 sensor already. If you erase the memory, the values can go + or - for while until the mixtures trims are adjusted by the ECM. Once they are adjusted, the values in 33 will be close to zero. You can check MVB 32 for the fuel mixture adjustments done by the ECM. Fields 1 & 3 should not be greater than 5% + or - and fields 2 & 4 should not be more than 10% + or -. If they are, you will get lean or rich faults.

djtalon

cool thanks, i will check them on friday hopefully if i get the ross tech. when i check the codes i get either multiple misfire or cylinder 4. not both and i dont get those codes every time.

how do i check for a broken wire from 02 plug to ecu?

ezveedub

Misfire codes should be P0300 and P0304 (cylinder 4) for what your saying you're getting. You always get P0300 with any misfire detected plus the DTC(s) for the cylinder(s) misfiring.

Checking the wiring will require removing the ECM and locating the pin location for Bank 2 sensor 1. Ohm test the wire from the O2 sensor to the ECM pin in the harness side and check for an open circuit.

djtalon

hey also not sure if this makes a difference but in this car ( s4) the temp guage rarly hits 1/2 mark. usually it is a bit lower than than. also takes along time to get warmed up. Of course this is compared to my wifes allroad 2.7t


could this cause the problem ?

ezveedub

It shouldn't cause the issues you have. Usually if you have a stuck or partially stuck open thermostat, you get a DTC fault for cooling system malfunction. You may have an instrument cluster with a temp gauge needle that's off though if it never reaches the middle.

djtalon

checked a couple of things and found a pulled wire from the connector on the car side.

thanks for the help!