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Home >> Jeep >> 2018 >> Grand Cherokee Laredo, RWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 8 (3.0L Diesel - DTCS P0627-00 To P1692-00) >> DTC Troubleshooting >> P0674-00-Cylinder 4 Glow Plug Circuit Open >> Diagnostic Test

Diagnostic Test

WARNING: This page is about a different variant/trim than selected.
  1. READ AND RECORD DTCS AND ENVIRONMENTAL DATA - ERASE DTCS AND CHECK FOR DTC TO RETURN 
    1. Using the scan tool, read DTCs in all Electronic Control Units (ECUs) and record on the repair order.
    2. For future reference, using the scan tool, run and save a Vehicle Scan Report and all recorded data.
    3. With the scan tool, erase all DTCs.
    4. Perform several ignition cycles leaving the ignition on for at least 10 seconds then off for 10 seconds.
    5. Turn the ignition on.
    6. Using the When Monitored and Set Conditions above and recorded data, operate the vehicle under the conditions that set the DTC.
    7. Using the scan tool, read DTCs.

      Did the DTC return as Active or Pending?

      Yes 

      • Go To  2

      No 

      • Perform the appropriate INTERMITTENT CONDITION diagnostic procedure. Refer to INTERMITTENT DTC .
  2. CHECK FOR OTHER DTCS 
    1. Refer to the recorded DTCs.

      Are DTCs P052F-00, P0683-00, U0106-00, U0407-00, or any other Glow Plug Module Performance fault codes active or pending?

      Yes 

      • Perform the applicable diagnostic procedure(s) for those Diagnostics before continuing with this one. Refer to DIAGNOSTIC CODE INDEX .

      No 

      • Go To  3
  3. ISOLATE AND LOAD TEST THE (A208) GLOW PLUG 1 CONTROL CIRCUIT TO CHECK FOR HIGH RESISTANCE 
    1. The ignition must be off when performing a load test on a circuit.
    2. Isolate the circuit by disconnecting the PCM and every component harness connector containing the circuit being tested.
    3. Connect the positive lead of the load test tool to the positive side of the Battery (A). Note:  Refer to the diagram below.
    4. Using an approved back probe tool, connect the negative lead of the load test tool to the circuit being tested at one of the component harness connectors (B).
    5. Using an approved back probe tool and a fused jumper wire, connect the circuit being tested to the negative side of the Battery or a known good ground at the other component harness connector (C and D).
    6. The bulb on the load test tool should be illuminated and bright if there is no resistance in the circuit.
      NOTE:

      Why load test a circuit?  A load test is used to determine if a circuit is capable of carrying the amperage needed to perform properly. The 3156 bulb in the load tool illustrated, is a simple but effective method of testing circuit functionality. A 3156 Bulb has approximately 6.0 Ohms of resistance when the bulb is powered  and draws approximately 2.0 amps of current. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to STANDARD PROCEDURE .

      NOTE:

      A 12-volt test light can be substituted for the load test tool, but only  if the test light draws enough current to effectively load test the circuit. Many high impedance test lights draw very little amperage (less than 0.1 amps) and are not reliable to load test a circuit. To perform a proper load test of a circuit, the tool being used should draw more than approximately 0.75 amps.

      NOTE:

      Why perform a Voltage Drop Test?  To verify with certainty there is not any resistance in the circuit being tested, perform a simple voltage drop test across the 3156 bulb of the load test tool. To do so perform the following:

      • 1. Connect the leads of a DMM to the alligator clips on the load test tool while the load test tool is connected in series with the circuit.
      • 2. Compare the voltage drop across the bulb to the voltage reading across the Battery terminals.
      • 3. The voltage dropped across the bulb should be equal to the voltage reading across the Battery terminals if there is no resistance in the circuit being tested.

      Example:  2.0 Ohms of resistance in the circuit being tested will cause the voltage measurement across the bulb to be 25% less than when compared to Battery voltage. The reason for this is that the 2.0 Ohms in the circuit makes up 25% of the total circuit resistance of 8.0 Ohms. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to STANDARD PROCEDURE .

      GC0174954Courtesy of CHRYSLER GROUP, LLC
      WARNING:

      To avoid possible serious or fatal injury, DO NOT load test any air bag/restraint system components or circuits using the procedures listed here. Refer to the Service Information for proper air bag/restraint system testing procedures.

      CAUTION:

      Do not load test any circuits with components still connected to the circuit.

      NOTE:

      When probing a circuit at an Electronic Control Unit (ECU) harness connector, always use an appropriate back probing tool to prevent any possible damage to the ECU terminals.

      NOTE:

      Compare the brightness of the bulb in the load test tool to that of a direct connection to Battery.

      Is the load test bulb illuminated and bright?

      Yes 

      • Go To  4

      No 

      • Repair the circuit for an open or high resistance.
      • Perform the VVV VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  4. ISOLATE AND LOAD TEST THE (A29) FUSED B+ CIRCUIT TO CHECK FOR HIGH RESISTANCE 
    1. The ignition must be off when performing a load test on a circuit.
    2. Isolate the circuit by disconnecting the PCM and every component harness connector containing the circuit being tested.
    3. Connect the positive lead of the load test tool to the positive side of the Battery (A). Note:  Refer to the diagram below.
    4. Using an approved back probe tool, connect the negative lead of the load test tool to the circuit being tested at one of the component harness connectors (B).
    5. Using an approved back probe tool and a fused jumper wire, connect the circuit being tested to the negative side of the Battery or a known good ground at the other component harness connector (C and D).
    6. The bulb on the load test tool should be illuminated and bright if there is no resistance in the circuit.
      NOTE:

      Why load test a circuit?  A load test is used to determine if a circuit is capable of carrying the amperage needed to perform properly. The 3156 bulb in the load tool illustrated, is a simple but effective method of testing circuit functionality. A 3156 Bulb has approximately 6.0 Ohms of resistance when the bulb is powered  and draws approximately 2.0 amps of current. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to STANDARD PROCEDURE .

      NOTE:

      A 12-volt test light can be substituted for the load test tool, but only  if the test light draws enough current to effectively load test the circuit. Many high impedance test lights draw very little amperage (less than 0.1 amps) and are not reliable to load test a circuit. To perform a proper load test of a circuit, the tool being used should draw more than approximately 0.75 amps.

      NOTE:

      Why perform a Voltage Drop Test?  To verify with certainty there is not any resistance in the circuit being tested, perform a simple voltage drop test across the 3156 bulb of the load test tool. To do so perform the following:

      • 1. Connect the leads of a DMM to the alligator clips on the load test tool while the load test tool is connected in series with the circuit.
      • 2. Compare the voltage drop across the bulb to the voltage reading across the Battery terminals.
      • 3. The voltage dropped across the bulb should be equal to the voltage reading across the Battery terminals if there is no resistance in the circuit being tested.

      Example:  2.0 Ohms of resistance in the circuit being tested will cause the voltage measurement across the bulb to be 25% less than when compared to Battery voltage. The reason for this is that the 2.0 Ohms in the circuit makes up 25% of the total circuit resistance of 8.0 Ohms. Read the CIRCUIT LOAD TESTING PROCEDURE for information on building a simple load test tool and for additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to STANDARD PROCEDURE .

      GC0174954Courtesy of CHRYSLER GROUP, LLC
      WARNING:

      To avoid possible serious or fatal injury, DO NOT load test any air bag/restraint system components or circuits using the procedures listed here. Refer to the Service Information for proper air bag/restraint system testing procedures.

      CAUTION:

      Do not load test any circuits with components still connected to the circuit.

      NOTE:

      When probing a circuit at an Electronic Control Unit (ECU) harness connector, always use an appropriate back probing tool to prevent any possible damage to the ECU terminals.

      NOTE:

      Compare the brightness of the bulb in the load test tool to that of a direct connection to Battery.

      Is the load test bulb illuminated and bright?

      Yes 

      • Go To  5

      No 

      • Repair the circuit for an open or high resistance.
      • Perform the VVV VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  5. CHECK THE GLOW PLUG 4 FOR PROPER OPERATION 
    1. Turn the ignition off.
    2. Replace the Glow Plug in accordance with the Service Information. Refer to PLUG, GLOW, 3.0L DIESEL, REMOVAL .
    3. Turn the ignition on.
    4. With the scan tool, erase PCM DTCs.
    5. Perform several ignition key cycles leaving the ignition on for at least 10 seconds per cycle.
    6. With the scan tool, read PCM DTCs.

      Does the scan tool display this DTC?

      Yes 

      • Go To  6

      No 

      • Replacing the Glow Plug repaired the condition.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
  6. CHECK RELATED GLOW PLUG MODULE HARNESS CONNECTIONS 
    1. Disconnect the Glow Plug Module harness connector.
    2. Disconnect all related in-line harness connections (if equipped).
      NOTE:

      There are several component harnesses connected to the Glow Plug Module including: The Glow Plugs, the PDC, and the PCM.

    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.
      • Look for any chafed, pierced, pinched, or partially broken wires.

      Repair any conditions that are found.

    5. Connect the Glow Plug Module harness connector. Be certain that all 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 the related component harness connectors. Be certain that all harness connectors are fully seated and the connector locks are fully engaged.
    8. Using 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 as Active or Pending?

      Yes 

      • Replace the Glow Plug Module in accordance with the Service Information. Refer to REMOVAL
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .

      No 

      • The wiring or poor connection problem has been repaired.
      • Perform the PCM VERIFICATION TEST. Refer to PCM VERIFICATION TEST .
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