A-9 ~ PCM Output Drivers

PCM Output Drivers Circuits:

Circuit 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 or groups of 7, called either a surface mounted Quad Driver Module), which can independently control up to 4 output PCM terminals or Output driver Modules which can independently control up to 7 outputs. Not all outputs are always used. When and output is "ON," the terminal is grounded and the terminal voltage will normally be low. When an output is "OFF," the terminal voltage normally will be high.
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, too much current will flow into the driven The driver senses this and the output is turned "OFF" or the internal resistance increases to limit current flow and protect the drivers. The result is high output terminal voltage when the voltage should be low. If the circuit for B+ or the component is open, or the control side of the circuit is shorted to ground, terminal voltage will be low, even when the output is commanded "OFF." Either of these conditions is considered to be a driver fault.
Drivers also have a fault line to indicate the presence of a current fault to the PCM. A scan tool displays the status of the driver fault lines as "0" = OK, "1" = Fault.

Diagnostic Aids
The scan tool has the ability to command certain components and functions "ON" and "OFF." If a component or function does not have this capability, operate the vehicle during its normal function criteria to check for an open or shorted circuit.
An open or short to ground will appear in the open positions only when it is not commanded by the PCM. A short to voltage will appear in the short position only while the component is being commanded by the PCM.

Table A-9 - PCM Output Drivers:

Test Description
Test Description Numbers below refer to the step numbers on the Diagnostic Table.
1. The On Board Diagnostic (OBD) System Check prompts the technician to store the Freeze Frame Data in the scan tool. This will create an electronic copy of the freeze frame data taken when the fault occurred that can be referred to later.
2. A "1" in any of the positions indicates that a open or short is present in the corresponding circuit for that position.
3. Refer to the Scan Tool Display illustration to determine which circuit corresponds to which position of the display.
4. An open or short to ground will appear in the open positions only when it is not commanded by the PCM while a short to voltage will appear in the short positions only while the component is being commanded by the PCM.
5. Proper operation of any component or function with no "1" in any of the positions indicates that system operation is normal at this time.
6. A component or function that failed to operate at this point indicates that the fault is not on the PCM side of the circuitry. Go to On Board Diagnostic (OBD) System Check.

Initial Inspection

9. When the scan tool indicates a fault after disconnecting the component electrical connector and verifying that no open or short is present in the circuit, then the PCM is faulty.
10. The "1" going away after disconnecting the component electrical connector indicates that the component or component side wiring is at fault.