Question about 2004 GMC Envoy

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My service engine soon light was on. I took the vehicle to a mechanic and the code came back po422. A smoke check was performed and they said it had a leak in the filler neck and the entire gas tank needed to be replaced. So the dealer replaced the tank and now I'm getting a loose gas cap message light on the dash. Since the dealer did not replace the cap when replacing the tank is that what the problem is, or was it not the gas tank issue at all?

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If they forgot to tighten the hose clamps on the hose from the tank to the filler cap it could be setting it off. If they are all tight it was probably just the gas cap. The gas cap is usually ALWAYS the culprit. Let me know if this helps

Posted on Jan 19, 2011

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2004 GMC Envoy, My service engine soon light came on. I took the vehicle to a mechanic and the code came back po422. A smoke check was performed and they said it had a leak in the filler neck and the...


Hello: Without being there when the smoke test was performed no one can say what the results of the smoke test were. I would go back to the dealer and speak to the service director/service manager and request a new gas cap.

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Service engine soon light came on


The computer or ECM constantly tests operation of all sensors and components. When any of the sensor signals is missing or out of normal range, the ECM sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECM memory.

The same happens if a mechanical component of controlled system fails. For example, mechanical problem inside the transmission also can turn the "check engine" light on. Even not properly closed gas cap will cause the "check engine" light to come on - the ECM constantly checks if the gas tank is sealed properly.

To sum up, when the "Check Engine" or "Service Engine Soon" light comes on and stays on, there is a problem with your vehicle. This could be a problem with the engine, transmission, or some emission-related component or system.

The stored trouble code can be retrieved with the special scan tool by the technician. The code itself does not tell exactly which part to replace, it only gives a direction where to look for - the technician has to perform certain tests specific for each code to find the exact cause of the problem.

Scanning for knowed exactly what fault code you have there.

Tell us news (remember rated this post).

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All modern vehicles have a computer or the ECM (Electronic Control Module) that controls the operation of the vehicle powertrain (the engine and transmission). The main purpose of this is to keep the engine running at top efficiency with the lowest possible emissions. With constantly growing demands for better fuel economy and new strictest emission regulations it's not very easy to achieve. The engine parameters need to be constantly and precisely adjusted according to various conditions such as speed, load, engine temperature, gasoline quality, ambient air temperature, road conditions, etc. That's why today's cars have much more electronics than in early days - there is a large number of various sensors and other electronic devices that help the vehicle computer or ECM to precisely control the engine and transmission operation and monitor emissions.
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Our check engine light was on and we got the diagnostic and it was the gas cap and they reset the codes so the check eng ligh was off for almost two weeks before we took it back for the emission and...


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