3T40 Transmission

Code Chart 26:

Quad-Driver Circuit:

CIRCUIT DESCRIPTION:
Quad-Driver Modules (QDM) are used to control the components shown in the illustration above. When the ECM is commanding a component "ON," the QDM closes the switch completing the circuit to ground. Each QDM output has a sense line. When a component is commanded "ON," the voltage potential on the sense line is low, and when the component is commanded "OFF" the voltage potential on the sense line is high. DTC 26 will set when the ECM is commanding a component "ON" and the voltage potential on a QDM "A" sense line is high, or if the component is commanded "OFF" and the voltage potential on a QDM "A" sensor line is low. Either of these conditions will cause the QDM "A" fault line to display HIGH and set DTC 26. On all vehicles, the QDM "A" fault status on the scan tool will display HIGH with the brake applied or if the engine is not running. On vehicles with a 3T40 transmission, the QDM "A" fault status on the scan tool will read HIGH until the TCC in-line switch is closed. These conditions will not cause DTC 26 to set even though the fault line displays HIGH. To simulate driving in second gear and change the QDM status to low, disconnect TCC connector and connect a test light between harness terminals "A" and "D."
DTC 26 will set if:

^ The system is running in "CLOSED LOOP."
^ Brake switch is closed (brake not applied).
^ Transaxle in mid or high gear.
^ The ECM detects an improper voltage level on a QDM "A" controlled circuit for 10 seconds.

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 related harness connectors, including 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, ensure that the mid gear switch and CKT 446 is not open with the vehicle operating in Park/Neutral or first gear. This condition can cause a false DTC 26 to be set. Refer to DTC 27 chart for diagnosis. If DTC reoccurs with no appearent connector problem, replace ECM.