Diagnostic Test

WARNING: This page is about a different car, the 2024 Jeep Grand Cherokee L. However, it is still accessible from the selected car via links, so may be relevant.

READ AND RECORD DTCS AND ENVIRONMENTAL DATA - ERASE DTCS AND CHECK FOR THE DTC TO RETURN
1. With the scan tool, read DTCs in all Electronic Control Units (ECUs) and record on the repair order.
2. For future reference, with the scan tool, run and save a vehicle Scan Report and all related recorded data.
3. With the scan tool, erase all DTCs.
4. Turn the ignition off for a minimum of 10.0 seconds.
5. Turn the ignition on.
6. Using the When Monitored and Set Conditions above and recorded data, operate the vehicle in the conditions that set the DTC.
7. With the scan tool, read DTCs.
  Did the DTC return?
  
  Yes
  - Go To 2
  No
  - Perform the INTERMITTENT CONDITION diagnostic procedure. Refer to INTERMITTENT CONDITION .
CHECK THE ALTERNATOR AND ENGINE BLOCK FOR PROPER GROUNDING
1. Verify that the alternator is properly grounded to the engine.
2. Verify that the engine block is properly grounded to the battery and chassis.
  Are the alternator and engine block properly grounded?
  
  Yes
  - Repair the poor grounding issue,
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  No
  - Go To 3
CHECK THE (K20) ALTERNATOR FIELD CONTROL CIRCUIT FOR A SHORT TO VOLTAGE
WARNING:
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
1. With the scan tool, monitor the Duty Cycle reading for the Alternator.
2. Using a voltmeter, back probe the (K20) Alternator Field Control circuit at the Alternator harness connector.
3. Start the engine and monitor the scan tool and
4. Measure the voltage on the (K20) Alternator Field Control circuit at the Alternator harness connector while also monitoring the scan tool reading.
  NOTE:
  During normal operation the typical duty cycle of the field control at idle with minimal loads is approximately 35-40%, which will equate to between 4.0 and 5.0 volts on the control circuit. Depending on the charging issue, the PCM can drive the duty cycle to, or near off (0%), which will equate to 0 volts. Or drive the duty cycle near full fielded (100%), which will equate to between 11.0 and 12.0 volts.
  
  NOTE:
  If the control circuit is shorted to voltage the actual circuit voltage will be much higher than the duty cycle being commanded by the PCM and read on the scan tool.
  
  Is the actual control circuit voltage much higher than the commanded duty cycle?
  
  Yes
  - Repair the (K20) Alternator Field Control circuit for a short to voltage.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  No
  - Go To 4
CHECK THE (K20) ALTERNATOR FIELD CONTROL CIRCUIT FOR AN OPEN/HIGH RESISTANCE
1. Turn the ignition off.
2. Disconnect the Alternator harness connector.
3. Disconnect the PCM C2 harness connector.
  CAUTION:
  Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install the GPEC Diagnostic Adaptor to perform the diagnosis.
4. Connect the (special tool #10436, Adapter, GPEC Diagnostic)
5. Measure the resistance on the (K20) Alternator Field Control circuit between the Alternator harness connector and the GPEC Adaptor.
  Is the resistance below 3.0 Ohms?
  
  Yes
  - Go To 5
  No
  - Repair the (K20) Alternator Field Control circuit for an open or high resistance. Make sure to check for a spread terminal at the PCM harness connector.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
CHECK THE (K20) ALTERNATOR FIELD CONTROL CIRCUIT FOR A SHORT TO GROUND
1. Check for continuity between ground and the (K20) Alternator Field Control circuit at the GPEC Adaptor.
  Is there continuity between ground and the (K20) Alternator Field Control circuit?
  
  Yes
  - Repair the (K20) Alternator Field Control circuit for a short to ground.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  No
  - Go To 6
CHECK RELATED HARNESS CONNECTIONS
1. Disconnect all PCM harness connectors.
2. Disconnect all related in-line harness connections (if equipped).
3. Disconnect the related component harness connectors.
4. Inspect harness connectors, component connectors, and all male and female terminals for the following conditions:
  - Proper connector installation.
  - Damaged connector locks.
  - Corrosion.
  - Other signs of water intrusion.
  - Weather seal damage (if equipped).
  - Bent terminals.
  - Overheating due to a poor connection (terminal may be discolored due to excessive current draw).
  - Terminals that have been pushed back into the connector cavity.
  - Check for spread terminals and verify proper terminal tension.
  Repair any conditions that are found.
5. Connect all PCM harness connectors. Be certain that all harness connectors are fully seated and the connector locks are fully engaged.
6. Connect all in-line harness connectors (if equipped). Be certain that all connectors are fully seated and the connector locks are fully engaged.
7. Connect all related component harness connectors. Be certain that all connectors are fully seated and the connector locks are fully engaged.
8. With the scan tool, erase DTCs.
9. Test drive or operate the vehicle in accordance with the when monitored and set conditions.
10. With the scan tool, read DTCs.
  Did the DTC return?
  
  Yes
  - Replace and program the Powertrain Control Module (PCM) in accordance with the Service Information. Refer to MODULE, POWERTRAIN CONTROL (PCM), REMOVAL AND INSTALLATION .
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
  No
  - The wiring or poor connection problem has been repaired.
  - Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .