Sunfire L4-2.2L VIN 4 (1996)
Powertrain Control Module: Description and Operation
PCM Outputs (Qdsm & Odm)
DESCRIPTION
The Powertrain Control Module (PCM) controls most components with electronic switches which complete a ground circuit when turned "ON."
These switches are arranged in groups of 4 and 7, called either a surface mounted Quad Driver Module (QDSM), which can independently control
up to 4 outputs (PCM) terminals or Output driver Modules (ODMs) which can independently control up to 7 outputs. Not all outputs are always
used.
OPERATION
Drivers are fault protected. If a relay or solenoid is shorted, having very low or zero resistance, or if the control side of the circuit is shorted to
voltage, it would allow too much current flow into the PCM. The Driver senses this and the output is turned "OFF" or internal resistance increases
to limit current flow and protect the PCM and the driver. The result is high output terminal voltage when it should be low. If the circuit from B+ to
the component or if the component is open, or the control side of the circuit is shorted to ground, terminal voltage will be low. Either of these
conditions is considered to be a driver fault.
When and output is "ON," the terminal is grounded and its voltage will normally be low. When an output is "OFF," its terminal voltage normally
will be high.
QDSMs and ODMs also have a fault line to indicate the presence of a current fault to the PCM's central processor. A scan tool displays the status
of the ODM fault lines as "0" = OK, "1" = Fault.
