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1999 Chevy Tahoe 02 sensors

Tiny
THECOMMONYAK
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 106,213 MILES
I have a 99 Tahoe, its runs beautifully, but just recently the SES light came on. I got it checked out by GM and they said that both rear 02 sensor went out. But then he said its impossible for both to go out at the same time, so its got to be the wiring or the harness, is he right? Where is it on my truck, and is it possible for me to fix it myself?
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Tuesday, December 16th, 2008 AT 5:35 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi:
Yes it's possible to be a wiring problem. But it could also be that both sensors went bad. The sensors are attched to the exhaust system. Follow the wiring from them to check for damaged or broken wires.
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Tuesday, December 16th, 2008 AT 6:16 PM
Tiny
THECOMMONYAK
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  • 4 POSTS
Hey thanks, but do you think you can describe to me what to look for, where to start looking and how far along to go? Thanks
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Wednesday, December 17th, 2008 AT 7:44 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi:
Start at the O2 sensors. There will be wiring going to them that is exposed to really high temps. Check and make sure that they are not damaged. Then follow them back to the engine compartment. They will plug into the wireing harness. If the plugs are good and the wireing isn't damaged, chances are the wiring is good. Let me know what you find.

Joe
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Wednesday, December 17th, 2008 AT 9:24 PM
Tiny
THECOMMONYAK
  • MEMBER
  • 4 POSTS
Ok I will do that, I will start around the cat converter and work my way through. Now, do I need a special tool to remove the 02 sensor if its bad or not?
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Thursday, December 18th, 2008 AT 4:43 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
No special tool is needed. Just standard wrenches. I think it may be a 13/16.

Joe
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Thursday, December 18th, 2008 AT 8:57 PM
Tiny
THECOMMONYAK
  • MEMBER
  • 4 POSTS
Hey Ive looked at the cat and found the sensors, I looked at each one and they looked fine as well as the wires, but I didnt take out the sensor, so I dont know if the sensor is bad.I did notice a sensor or something similar sticking out a bit higher and it had the sleeve pulled back a bit. Could that maybe be it or what should I do?
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Friday, December 19th, 2008 AT 3:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi:
it sounds like you may be looking at the upstream sensors. What are they mounted to? Also, yes make sure it has a good connection.

Joe
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Friday, December 19th, 2008 AT 3:52 PM
Tiny
THECOMMONYAK
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  • 4 POSTS
Hey yeah that was it, I got it checked out and I bought two new sensors and the truck is running better, hopefully now I'll get better gas mileage. Thanks for your help.
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Saturday, December 20th, 2008 AT 4:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Great! Good luck, have a great Christmas, and if you run into other trouble, let me know.

Joe
Positive feedback is appreciated.
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Saturday, December 20th, 2008 AT 8:12 PM

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