Part 2 of 3

Code 26 Part 2 Of 2:

Code 26 Wiring Diagram:

***UPDATED BY TSB # 92-U-35A DATED OCTOBER 1992


CIRCUIT DESCRIPTION:


Quad driver modules (QDM) are used to to control several components shown in the wiring diagram. When the ECM is commanding a component "ON," the QDM closes the switch completing the circuit to ground. Each QDM has a sense line and a fault line.

When a component is commanded "ON" the voltage potential on the sense line will be "LO" and when the component is commanded "OFF" the voltage potential of the sense line is "HI."

Code 26 will set when the ECM is commanding a QDM (A) controlled component "ON" and the voltage potential on the sense line is high, or if the component is commanded "OFF" and the voltage potential on the sense line is Low. QDM (B) will NOT set a Code 26.

Vehicles with a 3T40 transmission will read HI until the second gear switch is closed. To check, disconnect TCC connector and connect a test light between terminals "A" and "D". This should cause the scanner to display "LO" for QDM (A) with the engine running.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

3. This test will determine which circuit is out of specifications.

DIAGNOSTIC AIDS:

^ Monitor the voltage at each terminal while moving the related harness connectors, including the ECM harness. If the failure is induced, the voltage will change. This may help locate the intermittent. Check for bent pins at ECM and ECM connector terminals. Also insure that the mid gear switch and circuit 232 is not open with the vehicle operating in park/neutral or 1st gear. This condition can cause a Code 26 to be set. Refer to Code 27 chart for diagnosis. If code re-occurs with no apparent connector problem, replace the ECM.