Diagnosis
The following table will diagnose the Powertrain Control Module (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 Diagnostic System Check - Cruise Control in Cruise Control. For specific system components and wiring refer to Wiring Repairs in Wiring Systems or refer to the transmission diagnosis portion of the service manual for transmission-related components.
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 and 7, and are called either a surface mounted quad driver module, which can independently control up to 4 outputs and PCM terminals, or an output driver module (ODM), which can independently control up to 7 outputs. Not all outputs are always used.
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 its internal resistance increases in order to limit the current flow and to 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 the component is open, or the control side of the circuit is shorted to ground, and the terminal voltage will be low. 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's central processor. A scan tool displays the status of the driver fault lines as 0 = OK, 1 = Fault. In order to correctly read the Short or Open PCM Output parameters on the scan tool, the ODM positions read from left to right: 7, 6, 5, 4, 3, 2, 1, 0. The actual pin-out locations for the PCM Output parameters are shown on the following tables:
ODM 1 Position | Pin-out |
|---|---|
0 | N/A |
1 | C2-59 |
2 | C2-55 |
3 | C2-54 |
4 | C2-58 |
5 | C2-56 |
6 | C2-57 |
7 | Internal PCM |
Output Driver 2 | |
ODM 2 Position | Pin-out |
0 | C2-46 |
1 | C2-45 |
2 | C2-50 |
3 | C2-53 |
4 | C2-51 |
5 | C2-52 |
6 | C2-52 |
7 | Internal PCM |
Refer to Schematics Engine Controls Schematics for the applicable pin-outs.
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 in order 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
The numbers below refer to the step numbers on the diagnostic table.
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The Powertrain On-Board Diagnostic (OBD) System Check prompts you to complete some basic diagnostics and to store the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data that was captured when the malfunction occurred. The scan tool stores this data for later reference.
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A one in any of the positions indicates that an open or a short is present in the corresponding circuit for that position.
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The one going away after disconnecting the component electrical connector indicates that the component or the component side wiring is malfunctioning. If the scan tool indicates a malfunction after disconnecting the component electrical connector and verifying that no open or short is present in the circuit, then the PCM is malfunctioning.
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An open or a short to ground will appear in the open positions on the scan tool only when not commanded by the PCM or the scan tool. 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.
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Proper operation of any component or function with no one in any of the positions indicates that system operation is normal at this time.
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Refer to the scan tool display art in this section in order to determine which circuit corresponds to which position of the scan tool display.
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The one going away after disconnecting the component electrical connector indicates that the component or the component side wiring is malfunctioning. If the scan tool indicates a malfunction after disconnecting the component electrical connector and verifying that no open or short is present in the circuit, then the PCM is malfunctioning.
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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 portion of the service manual for further diagnosis.
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Reprogram the replacement PCM and the perform the crankshaft position system variation learning procedure. Refer to the latest Techline™ information for PCM programming.
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If no malfunctions are present at this point, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
Is there a number 1 below any of the numbered positions in the Output Drivers? | -- | |||||||||
Disconnect the electrical connector to the component connected to the malfunctioning circuit. Is a number 1 still displayed in the corresponding Output Driver position? | -- | |||||||||
Command the output being checked with a scan tool while watching the corresponding position for each circuit. Do any of the positions change to a 1? | -- | |||||||||
Does the component or function operate when commanded? | -- | |||||||||
Was a repair necessary? | -- | |||||||||
Is a number 1 still displayed in the corresponding Output Driver position? | -- | |||||||||
8 |
Was a repair necessary? | -- | ||||||||
Is the action complete? | -- | -- | ||||||||
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Important: Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | -- | ||||||||
Does the system now operate properly? | -- | System OK |
