I have a 2005 Monte Carlo LS with 150k. The other day I was getting on to the highway and the car had a rough time accelerating once it hit 60MPH and eventually threw a code (P0131). The code said it is the O2 sensor in bank 1. I just replaced the spark plugs, spark plug wires, and coil packs, as well as the fuel pressure reg within the last 5k miles and the cat within 10k miles.


Is this definitely the O2 sensor or could it be another problem? Also it says bank 1, would this be the pre cat sensor and how difficult is it to replace? Thanks in advance for any help.

 

Very likely it could be. Precat is bank 1. Shouldn't be too tough to do.

 

Thank you for your response and sorry it took so long to get back on here. I have replaced the O2 sensor and am still having the same issue. The MIL light came back on shortly after replacing the sensor and it still bogs down pretty bad when trying to approach highway speeds mainly when I get to 60 it starts it will eventually regain power but usually i have to let off the gas a few times. Could this be issue be related to the EGR valve, MAF or Throttle position sensors? Thank again if anyone can help.

 

I wanted to add that I unplugged the MAF and drove the car around the block and the car drove perfectly, however I had an issue in the past and did this and replaced the MAF when I did, it didn't seem to fix the issue so I put the old MAF back in.

 

When the MIL came back on was it throwing the same code, or is it a diff code now ?

 

Have you checked the OXY SEN fuse located in the lower under hood fuse panel?

Is this the only code you are getting? If so check for loose/dirty/oxidized connectors or an open in the voltage and signal circuits for the O2 sensor. If the voltage signal drops and remain below 600 mV while under acceleration it will set the CEL.

If you have access to a scan tool that can read the code history and freeze frame data it would be a good idea to have that info retrieved. A lean condition under acceleration or a vacuum leak can also set the P0131 code because the signals received by the PCM may interpret an 02 heating circuit failure.

 

So I checked the Oxygen sensor fuse and it was fine, the engine is still throwing the same code p0131 and it is the only code coming up. I don't have access to a scanner that will tell me the voltage of the O2 sensor. As I stated before when I unplug the MAF the car drives normal and I know it is now the MAF. I would think this would eliminate any fuel issues and leave me with it being either a vacuum leak, the new O2 sensor being bad, or there is an open/short in the O2 wiring. It was a Bosch O2 sensor what are the chances the O2 sensor is bad?

 

Unplugging the MAF then having the car run 'normal' is NOT a diagnostic procedure to determine if the MAF is bad. When you unplug it the lack of signal from the MAF to the PCM makes the car run in open loop mode. In other words, the engine is running as if you had just started it. The PCM relies on the signals for engine temp, engine speed and throttle position to determine fuel delivery. Once the engine comes up to temp (and is receiving acceptable signals from ALL sensors including the MAF) the PCM switches over to closed loop mode.

The first thing I would do is unplug the connector and check the voltage supply and ground circuits. Connect the positive probe of your meter to terminal 3 of the connector. Connect the negative probe to terminal 2. Turn the key to the ON position and observe the voltage reading. You should have 12 volts. If you don't, check the power wire from the MAF to the power distribution center - including the ground. Once you are seeing 12 volts wiggle and pinch the length of the wiring harness looking for an open in the circuit. Also check the connector for oxidation/corrosion. Clean if needed. If everything checks out okay then the MAF should be monitored with a scan tool during a test drive. If the MAF isn't within spec or respond as it should, THEN replace it.

 

03SSLE, I made a typo I meant to say it is not the MAF.