P0135, P0141, etc.

[samgm2]

O2 Sensor Heater Circuit Failure. I've been trying to deal with this issue for a while and I just can't seem to resolve it.

1. The O2 sensors show about 10 ohms on the same color wires.
2. I verified that there is 12V on those wires when the ignition is turned to ON (not running but PCM getting power and AC is switched on).

The harness I got, unfortunately, doesn't have connectors for the rear O2 sensors (which really sucks). Thinking of adding them.

Does anyone know where I can get additional pins for the PCM connector so I can run my own O2 sensor connectors?

Does anyone have any idea why the circuit thinks it is failing? The fact that I get heater power would seem to indicate that the PCM driver is OK but I am just not sure.

[gtstorey]

A lot of time the ECM driver is grounding the heater circuit as the control. I replaced an 09 Cobalt SS ECM recently because of a failed grounding driver.

[Alvin]

Having the rear o2's wouldn't' help this situation.

Can you post a log? Might help us diagnose. . I think lazy o2 sensors will sometimes cause a heater code.

[edcmat-l1]

2. I verified that there is 12V on those wires when the ignition is turned to ON (not running but PCM getting power and AC is switched on).

This could be your issue if you do indeed have 12 volts on both wires. That would mean they're not grounded. If they were grounded, you'd have voltage on ONE wire, not both.

Would help to know what vehicle or PCM BTW. GEN3 vehicles the O2 heaters were grounded. GEN4 vehicles the PCM did the grounding.

[samgm2]

Both of the sensors are brand new (AC Delco). This is a P59 ECM (Gen 3). I tested the voltage at both pins on the sensor connector. Not a pin and the chassis. The sensors aren't lazy. I get reasonably rapid transitions. The truck is running perfectly. I think that I will pull the O2 Sensor out, turn on ignition and wait a couple of minutes and see if it gets hot. Interesting that on GEN 3, the 12 V is switched. You don't see a lot of applications with pFETs. nFETs are generally better and cheaper at sinking current.

[gtstorey]

Need to check with a test light to see if they will actually carry current.

[edcmat-l1]

With the sensors plugged in you need to check for voltage on one side of the heater and ground on the other. Those codes are set when the PCM does not sense a load on that circuit, i.e. no ground.