O2 sensor heater problem Need help of specialists
 

Code - p0135. Changed o2 sensors, MAF, and plugs. CEL is still on. Data on wires: Grey ground - OK, Black sensor data - OK, White heater 12V -OK, white heater - no ground. Could not find a wire diagram anywhere.
Questions: Is it a wire harness problem? Is there a relay between O2 sensors and ECU? Where it is located. How to test if ECU grounds the sensor?

RE: O2 sensor heater problem Need help of specialists
 

and what engine does that M-Class got?

RE: O2 sensor heater problem Need help of specialists
 

Sorry. ML320, 2000, 3.2 l engine. All 4 Os2 sensors have the same problem - heater. I am not aware of heater circuite diagram. Do the heater wires go directly to ECU or through a relay? Do they go separately to ECU (I doubt that), thus where is the meeting point? Thanks again

RE: O2 sensor heater problem Need help of specialists
 

ok, got it.

[IMG]local://upfiles/1/2407418D41C84930BA12CCEAC723B9AA.jpg[/IMG]

RE: O2 sensor heater problem Need help of specialists
 

.

[IMG]local://upfiles/1/394A22F904744AA09D53397B281DD5F5.jpg[/IMG]

[IMG]local://upfiles/1/627C2A35D9E545D5955C5C1585255FA3.jpg[/IMG]

[IMG]local://upfiles/1/2866AA043E9242DA903B7E95D38744A9.jpg[/IMG]

RE: O2 sensor heater problem Need help of specialists
 

Super. Thank you. So no relay, no common wire to the ECU. O2 sensors are working in pairs separately. The ECU transistors govern grounding of O2 sensors. I wonder if the ECU heater switch gets the signal from a temperature gage or from the O2 sensor itself? Can't read the ECU pin numbers, do you have a picture of ECU pins?
Thanks a lot