Diagnosis
The following table will diagnose the PCM controlled outputs from the output driver modules only. For diagnosis of the cruise control module circuit, refer to Cruise Control Diagnosis. For specific system components and wiring refer to Electrical Diagnosis or Transmission Diagnosis for transmission related components.
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
The numbers below refer to the step numbers on the diagnostic table.
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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 malfunction occurred. The information is then stored on the scan tool for later reference.
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A 1 in any of the positions indicates that a open or short is present in the corresponding circuit for that position.
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Refer to the scan tool display art in this section to determine which circuit corresponds to which position of the scan tool display.
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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.
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Proper operation of any component or function with no 1 in any of the positions indicates that system operation is normal at this time.
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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 Transmission, 8A or Engine Controls section for further diagnosis.
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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 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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Replacement PCMs must be reprogrammed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures.
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If no malfunctions have been found at this point, refer to Diagnostic Aids for additional checks and information.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to | ||
Install scan tool. Is there a number 1 below any of the numbered positions in the Output Drivers? | -- | |||
Check for an open or shorted circuit in any corresponding position (circuit) that contained a number 1 and repair as necessary. Was a repair necessary? | -- | |||
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? | -- | |||
Go to the appropriate Transmission, Electrical Diagnosis, or Engine Controls section table for any component that failed to operate when commanded and make any necessary repairs. Is the action complete? | -- | -- | ||
7 | Repair the short to voltage in the corresponding circuit for the position (circuit) that displayed a 1. Is the action complete? | -- | -- | |
Disconnect the electrical connector to the component connected to the malfunctioning circuit. Is a number 1 still displayed in the corresponding Output Driver position? | -- | |||
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Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
Operate vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK |
