[meyers]

Pulled the codes on my 02 2.8l 4motion with 130k today. It is giving me P0056, P0161, P0036 and P0141 which all relate to the Heater control circuit and O2 sensor heater circuit. Bank 1 and Bank 2 sensor 2 on both sides. The car is running great, with no issues. Since I just bought it I would like to fix this. Could both the sensors have gone bad or is it more likely I am looking st some kind of voltage issue for the heater circuit. I hate to replace the sensors if it is just a fuse or a simple fix. I did use the search but didn't really see anything exactly like this issue.

 

[Emry]

It all depends whether the previous owner had replaced the O2 sensors already. If not, then you need to change them. O2 sensors usually go to about 100K miles and after that become unreliable bound to break any time.

 

[Tomvw]

16420/P0036/000054 - Oxygen (Lambda) Sensor B1 S2: Heating Circuit: Malfunction / Open Circuit
16525/P0141/000321 - Oxygen (Lambda) Sensor B1 S2; Heating Circuit: Malfunction

This indicates an open circuit in the sensor, its connector, or its wiring.
Check with a meter.

 

[meyers]

I don't think they have ever been changed and have 130k on them. Was just thinking since they both had basically the same fault, maybe it was something in the circuit. I am going to change them just want to make sure there isn't some other fault in the system.

 

[sirwired]

I'd check with a meter at the O2 sensor plug before replacing. I agree that it's suspicious that both are logging the same fault. Looking at the wiring diagram, check resistance between Green-Yellow and Brown-Black for each rear sensor. (I think those are the ones with the reddish-brown plugs if the V6 is similar to the 1.8T.) And, naturally, look for voltage on those pins; I think it'll be on Brown-Black, as Green-Yellow appears to be a common ground for a bunch of engine parts on one of the sensors.

It is a bit of a puzzler, since both sensors have failed at once, but they connect to different pins on the ECU harness.

If you DO end up replacing the sensors, go with the Bosch replacements (Bosch is the OEM); the rear sensors should be fine with a "Universal" sensor listed for this application.

 

[Tomvw]

The Green/Yellow wire is common 12V+, note it is only active while the engine is cranking or running.
The Brown/Black wires are switched to ground by the ECU as required.