Hi everyone. 2003 Monte 3.4
I have an o2 sensor problem and I am going to give all the details I have.
First of all, I got a code P0135 o2 sensor bank 1 sensor 1 circuit malfunction.

Here's what I have done so far;
-Repaced the o2 sensor with NEW.
-checked connections, and condition of all wires, looks good.
-bought a complete service manual and performed the following tests on the o2 sensor..
1) used a test light and made sure there was power to the sensor.
2) put one end of the tester to the power wire of the sensor, and the other end to the low circuit wire, when I started the car, it illuminated. I left the wires connected and I turned the key to ON with engine OFF and it still illuminated.
Now according to the manual, it shouldnt light up without the engine running. Seeing the senor is new, and still getting the circuit malfunction, I replaced the Powertrain control module (PCM) and that did not correct the problem.
QUESTIONS:
-Will a minor exhaust leak cause an o2 sensor circuit malfunction? (The leak is in the exhaust pipe somewhere, not in the manifold or converter.)
-Does anyone know what what cause this malfunction other than a bad sensor or PCM?
Any advise will be great!! Thank you!

 

Hey so I copied your post and emailed it to my Monte builder. Will let you know what he thinks your issue may be. Might take a couple of days... Stand by........

 

You have a circuit failure, which means its more then likely wiring related. Eventhough you are getting power to the sensor, it may not be the correct voltage. Since you have a service manual, the next logical step would be to utilize a voltmeter and see if the O2 sensor is recieving the correct voltage compared to what the manual says.

-Exhaust leaks can throw off the PCM by giving the O2 sensor an incorrect reading with reduced airflow, but it would have to BEFORE the sensor in the manifold. Any exhaust leaks after is irrelevant and the sensor wouldn't know the difference since the air already passed through

-The good news is you aren't getting any lean/rich codes, so you can safely rule out engine performance issues such as misfire, vaccum leak, etc.

-It is the first sensor (sensor 1), so its before the catalytic converter and that can be ruled out. A failed cat can destroy sensor after sensor if not addressed

-You said you had the PCM replaced and reprogrammed, so the brain has been replaced...

So the problem lies between the sensor itself and the PCM. Some common failures are the harness plugs, plastic becomes brittle over time and may appear fine, but upon closer look can be breaking apart right where it meets the plug.

 

I agree - you need to do a physical inspection of the wiring between the PCM and O2 sensor and check for proper voltages at the connector. It's possible the insulation on the wiring harness may be worn/pinched which is causing the problem. Another possibilty is the O2 sensor itself - even though it is new. A lot of people have reported problems using aftermarket sensors. AC Delco or Delphi brand sensors are recommended. Other brands may not operate within OE spec and trigger the CEL.

 

Thanks Hammer and 03! I will definately check the issues mentioned. I do have the service manual but im still trying to figure out how to understand it and navigate through it. Here is another question I have:
-I have another code (cant remember the code) but its "TCC Clutch Circuit Stuck ON" and also, my airbag light is always on, and when I turn the key in the ignition to "start" I have to hold it there in the start position for a second before it will crank.
Any idea if these issues could be linked together somehow?

 

Well wanted to let you know what information I received from my mechanic. Hope your able to use these procedures and get to the bottom of your problem.


1. Verify amp value for bank 1 sensor 1 O2 sensor in PCM data if the scan tool lists it.

2. The amp value should be 0.25 to 0.85 amps.

3. If outside of this range, verify that the Pink wire to the bank 1 sensor 1 O2 sensor is steady, 13-14v.

4. Disconnect the PCM clear connector, turn key on.

5. Check bank 1 sensor 1 O2 sensor heater circuit amp draw, pin 37 Black/White wire to ground through your amp meter.

6. Check the sensor for an open, pin C to D.



That should help, most of the problems I have found with a heater circut malfuncion is a bad sensor. I have run across a fiew wiring problems and one odd bad batch of new sensors that were drawing too much current on inital start up. Make sure to have all the scan tool data already loaded when starting the engine first thing in the morning, graph the o2 amp data, that should reveal the problem. I put the test steps above so it will be easy to copy and paste a reply.



Matt Snell
Paul's Automotive and 4x4 inc.
48 E 9400 S
Sandy, Ut. 84070
801-255-7472