Check engine light

Jerry Donnell

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I have a ‘11 GT (5.0, 108K miles) with the check engine light on. Codes were for bad O2 sensors bank 1 sensor 2 and bank 2 sensor 1, I have changed both sensors. Now it is telling me that bank 2 sensor 1 has a low voltage code and the check engine light is on again. I took the upstream sensor back and installed a new one today (exchange because it is only two months old). Issue now is if I start it cold the check engine light comes on, but if it warms up, I clear the code, I can drive it and the light stays off. As soon as it cools off or cold start it will throw the code and the check engine light comes back. The car runs and idles normally no change in gas mileage or smoke from the exhaust. I’m at wits end trying to figure this out. Any comments or help would be welcome.
 

Jgt58

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Sounds like a short in the wires

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Jerry Donnell

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I was thinking about the short also, but why would it only throw the code if it is cold? If it is a short then wouldn’t it just throw the code even if it was cleared, at operating temp or not?
 

Jgt58

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That I don't have an answer to. The only way is to jack the car up and inspect all the wires to o2 sensors

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WNYGT5-0

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I was thinking about the short also, but why would it only throw the code if it is cold? If it is a short then wouldn’t it just throw the code even if it was cleared, at operating temp or not?
Think of it like an expansion joint in a bridge. when it’s cold there is a big gap in the joint and a big thud as you drive over it. When it’s hot out there’s nearly any gap and a seamless transition from bridge to road.
 

Jerry Donnell

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But with that being said, wouldn’t it stand to reason that the check engine light would come on when it’s warm instead of cold?
 

Juice

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What brand O2 sensors?
Almost sounds like a substandard sensor issue.
 

Sky Render

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You might have a short or open in the heater circuit to the sensor, so it wouldn't matter when it was warm. Two of the wires to an O2 sensor are for a heater to warm it up when it's cold so it operates faster.
 

Jerry Donnell

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I bought Bosch replacements, no one has the others in stock. Guess I’ll be ordering online
 

Juice

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I got my new upstream sensors at rockauto. I was getting a CEL only when running it hard. Seemed wierd at the time. Didnt actually believed it to be a bad upstream sensor.
But it was.
 

Jerry Donnell

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The code it’s throwing is a P0151 (low sensor voltage for longer than 2minutes) again only when it’s cold does it activate the CEL. Guess I’ll be looking for a short in the wiring harness. I replaced the sensor again yesterday and cleared the code after it was warm, drove it for over an hour and no light, let it sit for about two hours and restarted. It activated the CEL again with the same code.
 

Juice

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I have only seen wiring damage from some type of physical damage to the wires. Cut by sharp rubbing object or rodent damage. Should be easy to find with a visual inspection.
I have also seen melted wires from overcurrent. Clearly the fix is not a larger fuse.
 

WNYGT5-0

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I have only seen wiring damage from some type of physical damage to the wires. Cut by sharp rubbing object or rodent damage. Should be easy to find with a visual inspection.
I have also seen melted wires from overcurrent. Clearly the fix is not a larger fuse.
Yup do this I would check your pins as well.
 

Jgt58

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I bought Bosch replacements, no one has the others in stock. Guess I’ll be ordering online
Just so you know the OE manufacturer for motorcraft is NTK/NGK. I work In the parts business.

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Jerry Donnell

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I’m assuming the damage would be between the plug for the O2 sensor and the PCM, since the O2 sensor is new
 

Jgt58

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The big thing with o2 sensors are response time of readings. [emoji106]

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