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How many O2 sensors do I have?

Tiny
JERIMAN
  • MEMBER
  • 1996 GMC SIERRA
  • 136,100 MILES
Says on O2 sensor is the code Parts store computer says 2 required but I found 4 on truck how do I know which one is bad and could it be something else?

Just got truck last week
no real symptoms anything is wrong
Occasionally a high idle
The rear most(after the catalytic) o2 sensor looks new
1 sensor on driverside pipe close to manifold 2
On passenger side about 3 inches apart and before catalytic
Converter and then one after (looks new)
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Sunday, January 15th, 2012 AT 8:09 PM

7 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
The actual code # should tell you which 02 sensor. Bank 1, bank 2, sensor 1, sensor 2. WhaT is the actual code? If everything runs fine and no mil on, why worry about it? I didn't see your engine litre size listed?
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Sunday, January 15th, 2012 AT 8:20 PM
Tiny
JERIMAN
  • MEMBER
  • 3 POSTS
I have the print out
HO2S21 heater condition (Heated oxygen sensor Bank aa2 Sensor 1
It's a 305 v8 not sure about litre
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Sunday, January 15th, 2012 AT 9:12 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
If your saying the code refered to the heater circuit, that is the circuit you need to check. Replacing the 02 sensor may not help? Bank two is the passenger side bank, first 02 sensor.

Ras was here first.
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Sunday, January 15th, 2012 AT 9:37 PM
Tiny
JERIMAN
  • MEMBER
  • 3 POSTS
Ok thanks
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Sunday, January 15th, 2012 AT 10:17 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
No problem.
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Monday, January 23rd, 2012 AT 5:55 PM
Tiny
KRAUSEE
  • MEMBER
  • 5 POSTS
I have a 2013 Avanlanche with O2 sensor codes. 87,000 miles. I changed all four O2 sensors, still have an O2 error code.

I was told it could be a "ground" wire somewhere on the truck that is the cause, I can pull the ECM fuse and it goes away until days later, sometimes it goes away on it's own.

I ignore it. Another solution is to get an ECM tune and delete the downstream O2 sensor input but that's $$$$$$
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Saturday, September 9th, 2023 AT 5:11 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,895 POSTS
It sounds like a bad PCM. Please post your new question here, you must be logged in.

https://www.2carpros.com/questions/new

Cheers, Ken
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Monday, September 11th, 2023 AT 11:19 AM

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