Saturday, March 10, 2012

1993 Corvette Coupe Displays Code 26?

In this case the customer noticed Service engine light on dash and in scanning the error code 26 is shown.

In this case as per the  error code 26 the problem can be faulty EGR or faulty Vacuum relay controlling EGR or its issue with ECM.

In most of cases ECM checked out to be faulty.

The fault code that is setting is due to the Engine Control Module (ECM) sensing that one of the four outputs of Quad Driver 1 is drawing excessive current. The code sets to alert us to this so that continued over-current does not cause the failure of the ECM. Quad Driver 1 controls the Evap canister purge solenoid, the EGR control solenoid, the AIR solenoid relay, and the AIR bypass solenoid valve. What is likely happening is that under the heat of the engine one of these four solenoids is shorting out causing the code to set. With the fault present the ECM may shut these solenoids off to avoid burning up the quad driver, this may be why you can not test the EGR solenoid with the fault present. One way you can test the EGR solenoid in its failed state would be to test the resistance of the solenoid. I would also suggest to test the solenoid cold so that you have a base line to compare to. What I suspect is that you will find the EGR solenoid is shorting out with the engine hot, you will then see the resistance of the solenoid fall drastically to less than a few ohms. The solenoid will usually be in the 15 to 100 ohm range. I don't know the exact spec for the resistance of the solenoid. Yes you are correct the EGR solenoid is near the fuel rail and has a vacuum line that connects to the EGR valve. I would doubt that you are having an AIR problem as this system does not usually run unless at wide open throttle or just after cold start-up. If you suspect the EGR solenoid you could also disconnect the solenoid then clear the codes. If you drive the vehicle you will cause other codes to set related to the EGR solenoid, but if you don't get the 26 code then you likely have the culprit.

This details will help.
Thanks.

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