Part 1 of 3

DTC 26 - Quad-Driver (QDM) Circuit:

Quad-Driver (QDM) 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 has a sense line and a fault 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 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. The fault line, which can be monitored with the Tech 1, will read "HIGH" under these conditions. If the ECM detects a "HIGH" QDM A fault line when it expects a "LOW" one, it will illuminate the MIL (Service Engine Soon) and store DTC 26. QDM B will not set DTC 26.

Important
^ DTC 26 will not set even though the fault line scans "HIGH" under the following conditions:
- Ignition "ON"/engine not running.
OR
- Vehicle not operating in 2nd or 3rd gear.
OR
- Brake applied.

Vehicles with a 3T40 transaxle will read "HIGH" until the TCC in-line switch is closed. To check, disconnect TCC connector and connect a test light between terminals "A" and "D". This should cause the Tech 1 to display "LOW" for QDM A with the engine running.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. The ECM does not know which controlled circuit caused DTC 26 50 this chart will go through each of the circuits to determine which is at fault. This test checks the MIL (Service Engine Soon) driver and the MIL (Service Engine Soon) circuit.
2. QDM symptoms:
^ TCC - malfunctioning - DTC 39.
^ "Check gauges" or hot light - "ON" all the time/"OFF" during bulb check.
^ Cooling fan "ON" all the time or won't come "ON" at all.
^ Poor driveability due to 100% canister purge.