2002 330ci code question

[j cookie]

hey guys, im working on a 2002 330ci coupe with a five speed transmition. the car after being driven for apporximatly 600 miles had the MIL turn on. when i checked the codes, they were P0137 and P0171. Any idea as to why these would turn on? i monitored the 02 sensors and they are all functioning correctly. The long term fuel trim for bank one said it was 10.3 and for bank 2 it was 9.4. the short term just slightly moved around. any ideas as to what could be causing this problem? as of right now the light however is not lit. but i still feel as tho the long term fuel trims could be too high. any information would be a great help.


joe

[teilmeister]

I believe p0171 is fuel trim lean bank one, I don't know about the other one though

[bluskye]

P0137 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
P0171 System too Lean (Bank 1)

Im guessing one of the post cat O2 sensors on Bank1 is malfunctioning. I could be wrong, it could be one of the pre-cat sensors in the exhaust manifold since the ecu is reading a lean condition

[j cookie]

i figured it was prolly going to be a pre-cat issue. my next plan is to switch the 02 sensors and see if it throws a code for bank 2.

thanks for the help

joe

[thejlevie]

The usual failure mode for an O2 sensor is for it to indicate a leaner condition than actually exists, causing the DME to increase the fuel trim. O2 sensors that have 80-90k (or more) will typically be causing additive trims and have reached the end of their useful life. And only the pre-cat sensors are used for engine management. The post-cat sensors are merely to indicate operation of the catalytic converters.

That's not what's happening here. The DME is trying to lean out the mixture on one bank, which would make me think of an injector that's sticking open, a misfiring cylinder, or a fault in the DME.

Since the two faults are for different banks, they are unlikely to be related. Depending on the mileage, I'd either swap the pre-cat sensors or replace them. Only after sorting out the reason for the lean trim on bank 1 would I worry about the post-cat sensor on bank 2.
**EDIT* I meant to say "Since the two faults are for different reasons, they are unlikely to be related".

[bluskye]

The usual failure mode for an O2 sensor is for it to indicate a leaner condition than actually exists, causing the DME to increase the fuel trim. O2 sensors that have 80-90k (or more) will typically be causing additive trims and have reached the end of their useful life. And only the pre-cat sensors are used for engine management. The post-cat sensors are merely to indicate operation of the catalytic converters.

That's not what's happening here. The DME is trying to lean out the mixture on one bank, which would make me think of an injector that's sticking open, a misfiring cylinder, or a fault in the DME.

Since the two faults are for different banks, they are unlikely to be related. Depending on the mileage, I'd either swap the pre-cat sensors or replace them. Only after sorting out the reason for the lean trim on bank 1 would I worry about the post-cat sensor on bank 2.

Both faults point to BANK 1, same bank. The lean condition is definitely a pre-cat malfunction. As for which O2 sensor is Bank1 or Bank2 since we have two manifolds... I would just replace both since im already at it. When one fails, the other is on it's tail.

[bluskye]

i figured it was prolly going to be a pre-cat issue. my next plan is to switch the 02 sensors and see if it throws a code for bank 2.

thanks for the help

joe

Just unplug one, and it will tell you which bank it is =)

[j cookie]

bluskye, i know which oxygen sensor corisponds with the banks, i was going to swap them in order to check to see if it is actually malfunctioning or if its unrelated. if i swap them and the falt moves to bank 2 that means that it is definatly the o2 sensor and both will be replaced. if it stays at bank one, that means that there is a further issue.

again thank you for the great advice,

joe

[bluskye]

bluskye, i know which oxygen sensor corisponds with the banks, i was going to swap them in order to check to see if it is actually malfunctioning or if its unrelated. if i swap them and the falt moves to bank 2 that means that it is definatly the o2 sensor and both will be replaced. if it stays at bank one, that means that there is a further issue.

again thank you for the great advice,

joe

Wait a minute, arent O2 sensors/cats warrantied up to 80K miles or 10 years?

[j cookie]

as far as i know, only the cat is warrantied to that extent. The 02 sensors are not. anything can foul them so i highly doubt they would do that. It would be nice tho if they did.

joe

[bluskye]

as far as i know, only the cat is warrantied to that extent. The 02 sensors are not. anything can foul them so i highly doubt they would do that. It would be nice tho if they did.

joe

Ahh, ok. Let us know what turns up