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Old 06-13-2010, 11:28 PM   #1
INF3RN0666
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Drooping O2 Sensor voltage?

Hey

I have 2003 Buick Century 3.1. P0137 is set in the ECM. I stupidly changed the O2 sensor on the car and didn't solve that problem. Now, I plugged in my code reader and noticed that the O2 voltage is 0.45V when the key is in the "ON" position with the engine not running, but then starts drooping slowly to 0V.

I figure there's a short on the high signal wire to ground. How would I test that and how would I fix it?

Thx
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Old 06-14-2010, 01:10 AM   #2
consultIII
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Re: Drooping O2 Sensor voltage?

the pcm supplies a bias voltage of 0.45v koeo and untill the car goes into closed loop; this is normal. the dropping to zero isn't.

before you check for short to grd; disconnect the 02 sensor connector grd the tan/white wire (low signal circuit) then turn the key on. check you scan tool reading for the o2 sensor. If its less than 30mv check for short to grd on high signal circuit.

key off. disconnect ecm connector and 02 connector. grd the purple/white wire. reading ohms on your voltmeter should be ol if wiring is ok. if shorted will give you a resistance reading.
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Old 06-14-2010, 08:48 AM   #3
INF3RN0666
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Re: Drooping O2 Sensor voltage?

Thanks for your help consultIII. I just wanted to clarify one thing. For the second reading where I "disconnect the ECM and ground the high signal wire", where am I measuring the resistance? Where do I put the multimeter's probes.

Suppose that both of these methods turn out that the wiring is ok. I'm assuming that means an ECM replacement. Also, if I replace the ECM, does it need to be reprogrammed by the dealership or can I just run the car without reprogramming?

THX SO MUCH!

Quote:
Originally Posted by consultIII View Post
the pcm supplies a bias voltage of 0.45v koeo and untill the car goes into closed loop; this is normal. the dropping to zero isn't.

before you check for short to grd; disconnect the 02 sensor connector grd the tan/white wire (low signal circuit) then turn the key on. check you scan tool reading for the o2 sensor. If its less than 30mv check for short to grd on high signal circuit.

key off. disconnect ecm connector and 02 connector. grd the purple/white wire. reading ohms on your voltmeter should be ol if wiring is ok. if shorted will give you a resistance reading.
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Old 06-15-2010, 12:04 AM   #4
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Re: Drooping O2 Sensor voltage?

you will be disconnecting the high signal wire at each end. So, if its good there should be no source to grd and the meter will read OL.

You can test at either end (which ever is easiest to access). black ohmmeter lead to chassis grd and red lead to the purple/white wire. Use a t-pin (available at sewing store...quilting tpin) and probe from the back of the connector if the terminials are small; you don't want to spread the female connectors and cause a pin fit problem.

If all is ok and the pin fit and connectors at the ecm are ok...very well could be pcm time. a new pcm must be programmed by the dealer. You could also get a used pcm from the wrecker and have it programmed to your vin. See if your dealer would do that and if its ok. a used pcm may or may not start the car due to the theft deterrant system.
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