PCM Outputs Diagnosis

*****This Procedure has been updated by TSB 71-65-64, October, 1997*****

Diagnosis
The following table will diagnose the PCM controlled outputs from the output driver modules only. For diagnosis of the cooling fan circuit, refer to Electric Cooling Fan Diagnosis.
For diagnosis of the cruise control module circuit, refer to Cruise Control Diagnosis. System Diagnosis - Cruise Control
For specific system components and wiring refer to the Electrical Diagnosis and the Automatic Transaxle for transmission related components.

Circuit Description
In order to correctly read the Short or Open PCM Output parameters on the scan tool, the 0DM positions read from left to right: 7, 6, 5, 4, 3, 2, 1, 0.

Refer to Wiring Diagrams / Engine Controls for applicable effected pin-outs. Electrical Diagrams

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 on the scan tool only when it is not commanded by the PCM or scan tool, while a short to voltage will appear in the short positions on the scan tool only while the component is being commanded by the PCM or scan tool.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.
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 art in this section to determine which circuit corresponds to which position of the scan tool display.
4. An open or short to ground will appear in the open positions on the scan tool only when it is not commanded by the PCM or scan tool, while a short to voltage will appear in the short positions on the scan tool only while the component is being commanded by the PCM or scan tool.
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 malfunction is not on the PCM side of the circuitry. Go to the appropriate Automatic Transaxle, Electrical Diagnosis or to the diagnostic table of the malfunctioning component for further diagnosis.
8. The 1 going away after disconnecting the component electrical connector indicates that the component or component side wiring is malfunctioning. If 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. malfunctioning.
9. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be be performed. Refer to the latest Techline information for PCM programming and the Powertrain Control Module for the Crankshaft Position System Variation Procedure. Testing and Inspection
10. If no malfunction have been found at this point, refer to Diagnostic Aids for additional checks and information.