Intermittent CEL - codes 161, 173 - PeachParts Mercedes-Benz Forum

mslc791 · #1 05-16-2007, 06:52 PM

Hello,

My wife's '99 ML 320 has on/off CEL. Codes 161 & 173 point to heating circuit malfunction for LR O2 sensor. The strange thing is that this sensor was replaced 1.5 yrs ago. Could it go wrong after such a short time?

mslc791 · #2 05-29-2007, 09:24 PM

I wanted to update you on this puzzling situation. I replaced the left rear O2 sensor, cleared the 2 codes (161, 173) by disconnecting the battery and after 10 driving cycles (the vehicle re-learned the proper fuel mixture ? per DVD), CEL is back on with the same 2 codes. Has anybody seen the same two codes and CEL in '99 ML320 (mine has only 66k) or in any MB?
Also, the auxiliary water pump stopped working - shoud run 10 mins after the engine shut-down, but all quiet on the western front.....I measured the voltage in the connector anf it is definitely getting 12.6V minutes after shut-off. Could these 2 be related i don't think so, but wanted to ask anyway.

Please, please help, I am getting desperate here

Thanks in advance.

mslc791 · #3 05-30-2007, 10:52 PM

I am trying this general section because nobody was able to help in M section.
The car is '99 ML320 w/66k. I have the above 2 codes and the car failed emission test. 161 is for heater on O2 sensor, so I checked wiring, the voltage is supplied to O2 after start. So I replaced RL O2 sensor and reset by disconnecting battery and after 10 starts learning cycle the car shows CEL again. Any ideas? Could it be perhaps the aging FL O2 sensor, as the system compares voltages received from both sensors? I just don't want to throw money into new parts that don't solve the problem.
Thanks in advance for helping me to put the car on the road again.

mbdoc · #4 06-01-2007, 08:09 AM

Code P0 161 means that the fuel computer isn't seeing the correct current draw from the left rear O2 sensor...causes, bad sensor or wiring..

Code P0 173 means that the fuel computer can NO longer change the fuel mixture on left side of the engine. ..possible causes, vacuum leaks, fuel pressure, OR air mass sensor.

Big QUESTION??? has truck has any catalyst recalls??

mslc791 · #5 06-01-2007, 12:01 PM

Thanks for response, MB DOC. The dealer did the catalyst campaign (checking for cracks - that's all that I was told was involved) in October 05, at which time they installed the new B2S2 (LR) O2 sensor, which is now the one throwing 161 code. I checked the wiring and this sensor is getting voltage (13.4) so it seems fine. Maybe I should replace the front O2, maybe as it ages it is affecting the rear one?