Misfire | 1998 Chevrolet Malibu | 3.1

Using Data PIDs to Diagnose Stuck Open EGR Valve on a 3.1

Have you ever had a car come in with a driveability complaint and only a P0300 misfire code? I am sure you have.This case study demonstrates why it is good to learn what normal scan data pids should be on the vehicles you commonly service.

When this 98 Chevy Malibu came in, it was running very poorly. It was missing on all cylinders,the idle was hunting around, it was a hard start, and just plainly sounded horrible. The check engine light was on with only a P0300 (multiple cylinder misfire) code stored. I always scan through the pid data see see where all the data values are in my diagnostic procedure. By doing this you learn known good values and can easily spot problems. I almost always start with fuel trims since this will point to me if it is a rich or lean issue, in most cases.

This car wasn’t is closed loop yet, so fuel trims weren’t active so I continued thru the rest of the scan data pids. The data pids that caught my eye was for the EGR position. Commanded EGR position was 0% but actual EGR position showed 100%. Problem found, now I just need to verify if it is actually open 100% and if it is, I have to see if it is stuck or if the control wire or driver is shorted to ground. I could also have a faulty EGR position sensor. The EGR on this 3100 is easy to access, so I just pulled the EGR valve and took a look. This valve was stuck wide open from carbon deposits. This is a fairly common issue. The carbon deposits build up on the pintle shaft and then the pintle binds up in the EGR valve. If this was a failure where a piece of carbon held the pintle of its seat instead, I would have just cleaned it, in most cases. A new EGR valve and this car was on it’s way.

Why didn’t this set a code? I don’t know. I see EGR position codes quite often but for some reason it did not set one on this car, for this particular failure. This shows you that you can’t always rely on the PCM to tell you what’s wrong by setting trouble codes, but instead you need to use the data that the PCM will give you.

Leave any questions or comments below. Thank you.

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Comments (4)

  1. kevin

    I have replaced EGR valve new plugs & wires new coil module has new fuel filter & pump getting good spark across all coils ?

  2. Katlin

    my car is running lean it is a 1999 malibu as well, i just wanted to know if this may be the actual cause of it?

    • James

      There is a plastic tube that runs from the PCV valve on the front valve cover then runs under the throttle cable support plate then into the back valve cover. The GM 3100 3400 engines only have this plastic tubing. There is a seal/grommet that is in the throttle body just under the throttle cable bracket. If you spray carb cleaner there while its running and the engine idles up. Its leaking. The same goes for any vacuum lines. To repair this you will need a new plastic tubing with grommet. When I bought my 2000 Malibu it had a major leak there setting lean codes. Also sometimes the EGR valve will get a chunk of carbon on it and it will hold it open causing a lean code and usually a EGR position codes. Normally those passages will clog up with carbon instead and you have to chisel out with coat hanger or stiff wire with carb cleaner to get the carbon out. It requires removing the throttle body and accessing the EGR port.

  3. hi I’m mr apilado,i have also Malibu 2002,my problem is therunning condition.when you start to drive the first gear and 2nd gear very noisy,i don’t know if something wrong to my compressor but still new.thank you

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