Low Coolant/Hot/Auto Trans Fluid Temp Lamp Circuit Fault

Low Coolant/Hot/Auto Trans Fluid Temp Lamp Circuit Fault:

Low Coolant/Hot/Auto Trans Fluid Temp Lamp Circuit Fault (Chart 3 Of 5):

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 driver to control the output. Each QDM has fault detection logic which compares QDM driver Input and output voltages. The logic expects to measure less than three volts when the QDM driver is On and greater than seven volts when Off. The QDM has only one fault line that will detect a fault on any of the four outputs. The Scan tool can be used to cycle the outputs On or Off. The Scan tool can also perform an automated test which can isolate the faulty circuit.

DTC Parameters
DTC P1640 and/or P1641 will set if:
^ There is an open, short to ground or short to voltage on the QDM output low coolant/hot telltale lamp circuit.
^ Fault detected for five seconds for P1641. Fault detected for 20 seconds for P1640.

IMPORTANT: The QDM circuit is continuously checked when the engine is running.

Diagnostic Aids
^ If one output is faulty, 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 Oft. When the quad driver cools down it will turn back On and this process will start over.
^ A shorted or open circuit or bulb can cause a DTC to set.
^ Check 10 amp IGN 1 in the IPJB.

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

Use the scan tool to diagnose the quad driver circuits and perform an off-board QDM test.

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 an intermittent fault, but more likely due to the way the fault detection works.

For example, if the SERVICE telltale lamp is Off, the PCM expects to refer to 12 volts on the circuit. If the circuit is open, zero volts will be measured on the circuit and the fault will be displayed. However, if the lamp is turned On the PCM expects to measure zero volts on the circuit, and will not detect a fault. This causes an intermittent problem because the lamp is not continously On.