Powertrain Controls - ECM/PCM

Diagnostic Chart - Part 1 Of 3:

Diagnostic Chart - Part 2 Of 3:

Diagnostic Chart - Part 3 Of 3:

Circuit Schematic:

Notice: Refer to TSB# 96-T-08 for updates to this test.


QUAD DRIVER OUTPUT FAULT
A quad driver module (QDM) is an electronic switch which completes a ground circuit when switched On. The QDM independently controls four separate outputs. A load is connected between battery voltage and the QDM allowing the QDM to control the output. Each QDM has fault detection logic which compares QDM input and output voltages. The logic expects to measure less than 3.0 volts when the QDM is On and greater than 7.0 volts when Off. Each QDM has only one fault line that will detect a fault on any of the four outputs.

DTC PARAMETERS

DTC 26 will set if:
^ There is an open or short on any of the QDM Output circuits.
^ Fault detected for 25 seconds.


DIAGNOSTIC AIDS

Component Resistance:
^ Linear EGR solenoid: 7 - 10 ohms (at 25°C (77°F ambient)
^ EVAP Canister Purge Solenoid: 20 - 50 ohms
^ Coolant Fan Relay: 70 - 90 ohms
^ A/C Relay: 70 - 90 ohms

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

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

^ If any corresponding codes have been set (example DTC 32) EGR valve 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, Dynamic Display or MIL telltale), 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 be 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.

^ Use Scan tool to verity QDM A or B and monitor specific output status of the circuits involved.