I am so new to this, so please be kind, I have a 99 ml302.with 145.000 miles. The check engine light went on the o2 sensor were the problem. it indicated the back 2. my husband changed the front and back, new air filter, tune up and new crankshaft sensor. The engine light was rest, but after 2 weeks of driving, the engine light came on again with the same two codes. What else could be causing this? thanks in advance.

 

Giving us the codes will help.

 

the codes are P0141 and P0161.

 

Both codes show that there is a problem with the heater circuit on each of the two rear O2 sensors.

It is doubtful that both sensors failed at the same time, but anything is possible. Fuse #19 supplies voltage to the O2 sensors, so disconnect the connectors to both rear O2 sensors, and with the key in the on position, check to see that you are getting battery voltage to the blue wire in the #1 position on each sensor.

If you are, then replace both rear O2 sensors, if not then you have an intermittent wiring problem. Post back with results.

 

Sorry I did not post sooner, computer crashed. I am getting voltage to both sensors. I replaced them and reset the codes. drove for over 40 miles engine light came back on with exact codes. for the same sensors. Is there anything else my husband can do?

Toni

 

First check sensor ground (W16) located at fire wall. Check for looseness and or corrosion.

Then conduct the tests for the heater circuit at the ECM (N3/10), using a Digital Volt/Ohm Meter which also has the capability of reading AMPS. Only disconnect connector B when instructed; all other connectors in place.

To obtain readings, pierce respective wires with small sewing pins. Wires1B and 2B readings are taken at the bottom of the connector as it will be disconnected.

 

Thank you soooo much. after taking off the cover we found one of the harnesses was loose. my husband re connected it and engine light did not go on after starting. Again thank you.