87121-ZW4-000 Honda MARK, RR. (50) (Honda Code 4683512).

The following background information is related to this procedure:The starting aid is used to improve the engine starting when the engine is cold. With the keyswitch in the ON position, the Electronic Control Module (ECM) will monitor the coolant temperature and the engine air inlet temperature to decide if the glow plugs need to be switched ON. If the glow plugs are required, then the ECM will activate the glow plug control unit for a controlled period. While the glow plug control unit is activated, the glow plug control unit will supply power to the glow plugs.Glow plugs are used for temperatures that are below 5° C (41° F).The GCU transmits a diagnostic signal back to the engine ECM. If the GCU detects a fault for one of the glow plugs, a diagnostic code will become active for that glow plug.
Illustration 1 g03770598
Schematic diagram for the glow plug starting aid circuit
Not all connectors are shown. Refer to the Electrical Schematic for the application.
Illustration 2 g02671559
View of the pin locations on the P1 connector for the Glow Plug Control unit (GCU)
(22) GCU diagnostic return
(52) GCU control signal
(41) GCU ground
Illustration 3 g02674096
View of the pin locations on the GCU
(1) Glow plug cylinder 3
(2) Glow plug cylinder 1
(3) GCU diagnostic return
(4) Battery +
(5) GCU ground
(6) Glow plug cylinder 4
(7) Glow plug cylinder 2
(8) Glow plug controlGlow Plug Starting Aid OverrideActivate this override using the electronic service tool. This override is used to check that the glow plugs are functioning correctly. The override will remain active until switched off using the electronic service tool.Navigate to the following menu options in the electronic service tool to access the "Glow Plug Starting Aid Override":
Diagnostics
Diagnostic Tests
Override Parameters
Table 2
Troubleshooting Test Steps Values Results
1. Inspect Electrical Connectors and Wiring
A. Check the fuses.
B. Inspect the terminals on the GCU. Refer to Troubleshooting, "Electrical Connector - Inspect" for details.
C. Inspect the connectors between the GCU and the glow plugs.
D. Inspect the terminals on the P1/J1 ECM connector and all other connectors associated with the glow plug circuit.
E. Perform a 30 N (6.7 lb) pull test on each of the wires in the ECM connector that are associated with glow plug circuit.
F. Check the harness for abrasion and for pinch points from the glow plugs to the GCU, and from the GCU to the ECM.
Damaged wire or connector
Result: A damaged wire or damaged connector was found. A fuse is blown.
Repair: Repair the damaged wire or the damaged connector. Replace any blown fuses
Use the electronic service tool to clear all logged diagnostic codes. Verify that the repair eliminates the fault.
Result: All connectors, pins, and sockets are correctly connected and/or inserted and the harness is free of corrosion, of abrasion or of pinch points.
Proceed to Test Step 2.
2. Check for Active Diagnostic Codes or Logged Diagnostic Codes
A. Connect the electronic service tool to the diagnostic connector.
B. Turn the keyswitch to the ON position. Do not start the engine.
C. Use the electronic service tool to override the glow plug start aid.
D. Check for active diagnostic codes or recently logged diagnostic codes.
E. Use the electronic service tool to turn off the glow plug start aid.
F. Turn the keyswitch to the OFF position.
Diagnostic codes
Result: A 5324-7, 5325-7, 5326-7, or 5327-7 diagnostic code is active or recently logged.
Proceed to Test Step 3.
Result: A 676 diagnostic code is active or recently logged
Proceed to Test Step 6.
Result: An active diagnostic code or a recently logged diagnostic code was not displayed.
Repair: To identify intermittent faults, refer to Troubleshooting, "Electrical Connector - Inspect".
3. Check the Glow Plug for the Suspect Cylinder
A. Turn the keyswitch to the OFF position.
B. Disconnect the connectors for the glow plugs in any suspect cylinders. Refer to Table 1 to identify which cylinders are suspect.
C. Use a multimeter to measure the resistance between the suspect glow plug connector and a suitable engine ground.
Resistance
Result: The measurement indicates an open circuit between the glow plug and the ground point.
The glow plug is faulty.
Repair: Replace the suspect glow plug. Refer to Disassembly and Assembly, "Glow Plugs - Remove and Install".
Use the electronic service tool to override the glow plug start aid and verify that the repair eliminates the fault. Clear all logged diagnostic codes.
Result: The measurement indicates that there is a resistance between the glow plug and the ground point.
The glow plug is OK.
Proceed to Test Step 4.
4. Check the Glow Plug Wiring for an Open Circuit
A. Turn the keyswitch to the OFF position.
B. Disconnect the connectors for any suspect glow plugs. Disconnect the connector for the GCU.
C. Use a multimeter to measure the resistance between the harness connector for the suspect glow plug and the appropriate terminal on the GCU connector.
Less than 5 Ohms
Result: At least