Girlfriend's car check engine - Help!

[BlueDragonVT]

Ok, here's the story. My girlfriend's 2005 Ford Police Interceptor has a check engine light on. We pulled the codes to see what we could do. She had a couple codes that were easily fixed by replacing the gas cap. She also had a couple of O2 sensor codes, including a P0161. We replaced the gas cap and O2 B1S2 and checked it, but we were still getting a P0161. We ran live data on the car and found that B2S2 was reading a stable 0.7xx with an occasional jump to 0.8xx, instead of constantly changing like the other three. We went back under the car and pulled B2S2. Since the code P0161 was supposed to be about the heating element, we also used a volt meter to check and make sure that the elemnt was getting power, and we read 11.5 volts, so that looked good. We swapped in a new O2 sensor. We now have new O2 sensors on both B1S2 and B2S2. We clear the codes and try again, and find that the P0161 code is still popping up, and now the live data shows B2S2 stuck at 0.000, with the occasional jump to 0.005. Still pretty stable, and not changing like the other 3 readings. At this point, I am all out of ideas. Can someone help me diagnose this issue, and how to fix it? She has to reregister her car this month, and that means passing an emissions test. Any help would be greatly appreciated. Thanks, all, and happy holidays!

[SS Blinder]

A code P0161 may mean that one or more of the following has happened:
HO2S heater power circuit open
HO2S heater ground circuit open
HO2S signal tracking (due to oil or moisture in the connector)
HO2S is damaged or has failed PCM has failed
Possible Solutions:
Replace HO2 Sensor
Repair open or short in power circuit
Repair open or short in ground circuit
Repair damaged connector due to tracking

I know you probably looked this up already, but from what you are describing and what you have done, I would look into using an electrical contact cleaner on the harnesses and see if that helps. you might have moisture or gunk in the harnesses. might have to inspect the wiring and repair/replace if needed

[Russell James]

Maybe you got another bad O2 sensor.

You could try swapping them side to side.

I believe P0161 is the heating element current fault.


"The ECM detects that the HO2S 2 heater current is greater than 2.9 amps, or less than 0.3 amps for greater than 8 seconds."

Grabbed that from a GM manual.

So somehow the current flow is out of whack on that circuit. See if your scan tool can read that heater element circuit in amps. Wiggle the connections while watching the amps. Make sure the male pins and female side of the connectors look good, put in some dielectric grease into all the cavities.

Beyond that, will need a service manual wiring diag view to see what terminal out of the ECM is that heater element output. Then check for batt voltage at that output terminal.

If there is no batt output at the ECM pin, bad ECM. Good batt voltage there, problem in the wiring or sensor itself.

[Russell James]

It looks like the ECMs look for amps there, not volts. So a high resistance connection or ground somewhere could cause the issue. Or a bad O2 heater element. Might show near normal volts at the connector, but amps out of whack once plugged in.

[BlueDragonVT]

So here's an update. We tried switching the B1S2 and B2S2 sensors, and the error code stayed on the B1S2 sensor, so it isn't the sensor. We chased the wires pretty much the whole length, and haven't found a wear spot, break, or short, and power seems to be getting to the heating element. Right now it looks like I've either got a problem with the grounding wire, or we have a problem with the computer.

I haven't tried cleaning the contacts where the wiring harness comes back to the computer, so I may try that next. I'll keep you guys updated, thanks for the help. If anyone else has any further advice or experience, I would appreciate it. Thanks, guys!

[VR Code R6P]

Originally Posted by Russell James

Maybe you got another bad O2 sensor.

You could try swapping them side to side.

I believe P0161 is the heating element current fault.


"The ECM detects that the HO2S 2 heater current is greater than 2.9 amps, or less than 0.3 amps for greater than 8 seconds."

Grabbed that from a GM manual.

So somehow the current flow is out of whack on that circuit. See if your scan tool can read that heater element circuit in amps. Wiggle the connections while watching the amps. Make sure the male pins and female side of the connectors look good, put in some dielectric grease into all the cavities.

Beyond that, will need a service manual wiring diag view to see what terminal out of the ECM is that heater element output. Then check for batt voltage at that output terminal.

If there is no batt output at the ECM pin, bad ECM. Good batt voltage there, problem in the wiring or sensor itself.

I would not use Dielectric grease in that circumstance. Dielectric grease is non-conductive. It would be fine on the rubber boot to keep the water out, but stay away from the terminals. Use a conductive grease on terminals.

[Russell James]

GM has a bulletin to use Dielectric grease part # 12377900 on ECM connectors. It should work good.

[Mark T]

Parts houses make a killing selling O2 sensors. Multiples more O2 sensors are sold then sensors that ever go bad.

[BlueDragonVT]

Final update: We got it fixed!

The real problem was a bad PCM. I bought it on Ebay for $75, and because this is a CVPE and has no PATS, I didn't have to get it reprogrammed. Plugged the new one in, and no more O2 codes. Unfortunately, it started throwing a catalytic converter code instead. Because she had let it go so long, the bad PCM had been doing a poor job managing the engine, and had completely clogged one of the CC's. We replaced it, and now everything is running smooth! Thanks to everyone that helped me figure this one out, I was really baffled there for a while!