Code 26 - Quad-Driver Error: Notes

The ECM is able to switch most components on/off through the use of an internal ground circuit. These ground circuits are arranged in groups of 4 outputs, called Quad-Driver Modules (QDM), which can independently control up to 4 outputs (ECM terminals), although not all the outputs are used. When an output is switched on, the terminal is grounded and its voltage will be low. When an output is off, its terminal voltage will be high, except for the TCC control which will also be low if the brake or 2nd gear TCC switches are open. QDMs are fault protected. If a relay or solenoid coil is shorted, having very low or zero resistance, or if circuit is shorted to voltage, it would allow too much current. The QDM senses this and turns off switch to protect QDM.

1. "Service Engine Soon" light is controlled by one QDM output and must be checked for each diagnostic check procedure.
2. Shift light is also QDM controlled. If shift light is on with engine off, cause can be determined using CHART C8C.
3. Grounding diagnostic test terminal causes QDM outputs to be turned on. This should turn shift light on.
4. Symptom may lead quickly to QDM circuit that has fault for outputs which have perceptible (noticeable) symptoms.
5. Trouble shoot other codes to see if Code 26 is eliminated. Code 53 indicates high battery voltage, which could cause higher current flow. Code 62 could indicate a 2nd gear switch problem that could be related to TCC QDM.