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ChRoNo16

04 Tahoe Running Lean

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My parents have a 2004 Chev Tahoe Z71, have a check engine light, ran my scan tool, it came up with error codes stating Bank 1 running lean, and Bank 2 running lean, but No O2 sensor codes... Anyone else have this happen or have an idea?

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You have almost no hope of fixing this without a service manual or an alldata subscription that provide the correct troubleshooting procedure. Save yourself the headache and get one of them.

 

That said, what can cause a lean condition? Too little fuel, ie fuel or regulator malfunctioning, or too much air, ie, vacuum leak.

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An easy check is to look real close at the air intake tube or duct and make sure there are no crack or loose. Either one would cause a lean condition on both banks.

 

Good Luck

Duelin

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My 2004 Suburban did exactly the same thing. I checked the air intake hose, cleaned the MAF and the throttle body, etc. Even put in new front O2 sensors. The engine ran fine, no change or reduction in fuel mileage, etc. 15 around town, 18 to 19 on the highway. The spark plugs did not show any sign of a lean condition.

 

I would clear the codes but they would come back after a while. Sometimes they would clear themselves but would be stored. I finally took the vehicle to a local vehicle electronics shop to have them diagnose the problem. When I explained that they were intermittent, the technician said the problem was either a bad connection in an O2 sensor connector, bad insulation on a O2 wire, or water getting into the wring loom at times causing a slight voltage change.

 

As the CEL was not on at the time, he said to be careful while running through water and washing the car so that lots of water didn't get sprayed up under the car. He said if the codes returned to bring it back and he would try to track done the exact cause. I followed his advice and the codes haven't returned for three months and 3000 miles of driving.

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