O2 sensor harness question
Thread Starter
Racer
Joined: May 2019
Posts: 316
Likes: 21
From: Michigan
O2 sensor harness question
Ihave a 2002 C5. My tuner said that my upstream O2's were grounded out, because they were very close on the readings they were giving. I looked up what the readings should be if they are a four wire plug, which they are.
Signal - black
Ground - Grey
White - Heater
The fuse is good, and there is no code. Is it possible the sensors themselves are bad, and not my wiring? Either way, he tuned it using my wide band.
What is the process to check both sides for a grounded situation such as mine? What values should I see at what point? Thanks.
Signal - black
Ground - Grey
White - Heater
The fuse is good, and there is no code. Is it possible the sensors themselves are bad, and not my wiring? Either way, he tuned it using my wide band.
What is the process to check both sides for a grounded situation such as mine? What values should I see at what point? Thanks.
Last edited by 2002 C5; Jun 15, 2025 at 01:50 AM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,597
Likes: 4,057
From: Cape Coral, Florida
Your tuner telling you that your upstream O2's are "grounded out" tells me he has no electrical experience whatsoever....what do you mean by..."because they were very close on the readings they were giving" ??...close to what ??....with the O2 heater fuse removed and the scan tool hooked up and ignition on you should see 450Mv's on the O2 sensors which is its bias voltage...if you see that the "sensor side" of the wiring is good...the heater circuit has 12 volts on one side and ground on the other....you can start there.
Thread Starter
Racer
Joined: May 2019
Posts: 316
Likes: 21
From: Michigan
When we were tunning the car, the O2 readings were almost exactly the same, and did not deviate far from each other. I will run the test you gave given later this week. Now I have to do the brakes all the way around on my wife's jeep. I'll post back up when I do. Thanks again.
