26 Quad Driver Output Fault

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A quad drive module is a semiconductor device capable of controlling four separate outputs. Each output of the QDM is an open collector driver which when turned on pulls the output to ground. A load is connected between 12 volts and the driver. When the output is turn on, current flows from the battery, through the load, through the driver to ground. Each QDM has a fault line feedback. A comparison of the driver input and output states is performed. If the input and output are in the same state, a fault will be detected. Each QDM has only one fault line that will detect a fault on any of the four

Code Parameters

Code 26 will set if there is an open or short on any of the QDM output circuits.

Diagnostic Aids

Components Resistances:

  • EGR Solenoid 20 - 50 ohms
  • Canister Purge Solenoid 20 - 50 ohms
  • Coolant Fan Relay 80 ohms
  • A/C Relay 80 ohms

NOTE: all resistance are ±10 ohms

A shorted or open solenoid, relay or bulb can cause a Code 26.

If one output is bad the PCM will shut down only that QDM output and not the entire quad driver unless the Quad driver reaches its thermal limit (short to voltage). At this time it will turn all four Quad driver outputs off. When the Quad driver cools down it will turn back on and this process will start over.

If any corresponding codes have been set: (Example Code 32) diagnose that QDM circuit first.

Check the tightness of the female terminal grip with the spare male terminal.

Use the Saturn Service stall system (if available) to diagnose the Quad Driver circuits.

When viewing "QDM FAULT" (using a scan tool or Dynamic Display), you may notice the fault appears to be intermittent. This may be due to it being an intermittent fault, but more likely is due to the way the fault detection logic works. For example, if the EGR solenoid is off, the PCM expects to see 12 volts on the sense line. If the circuit is open, 0 volts will bee seen, and the fault will be displayed. However, if the EGR solenoid is turned on (for instance at cruising speeds) the PCM expects to see 0 volts on the sense line, and will not detect a fault. In this example, the display would show "QDM FAULT A" at idle, but if the RPM is raised, the display will show "QDM FAULT NONE". When returned to idle, the fault will again be displayed.

NOTICE: When using the Saturn Service stall system to diagnose PCM/EC code 26, a PCM/TC code 51 may be set. Under these circumstances PCM/TC code 51 is a false code.