0393657 JOHNSON THERMOSTAT ASSY.

Table 1
Diagnostic Trouble Codes For The Glow Plug Starting Aid
J1939 Code Code Description Comments
676-5 Engine Glow Plug Relay : Current Below Normal The Electronic Control Module (ECM) detects a low current condition in the glow plug start aid relay circuit.
The ECM is unable to activate the relay for the glow plug starting aid. The glow plugs will not operate. The engine may be difficult to start in cold temperatures and the exhaust may emit white smoke.
676-6 Engine Glow Plug Relay : Current Above Normal The Electronic Control Module (ECM) detects a high current condition in the glow plug start aid relay circuit
The ECM is unable to activate the relay for the glow plug starting aid. The glow plugs will not operate or the glow plugs will operate all the time. The engine may be difficult to start in cold temperatures and the exhaust may emit white smoke.
Follow the troubleshooting procedure to identify the root cause of the fault. 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 ECM monitors the following parameters to decide if the glow plugs need to be switched ON:
Coolant temperature
Intake manifold air temperature
Air inlet temperatureIf the glow plugs are required, then the ECM will activate the starting aid relay for a controlled period. While the glow plug start aid relay is activated, the glow plug start aid relay will supply power to the glow plugs. If a "Wait To Start" lamp is installed, then this lamp will be illuminated to indicate the "Wait To Start" period."Wait to Start Lamp"This feature may be included as an option.When glow plugs need to be activated prior to starting, a lamp will indicate that the operator needs to "Wait to Start". Starting aids may be used during the cranking of the engine. Starting aids may be used if the engine has previously been started. The "Wait to Start" lamp will not be active in these conditions.Electronic Service Tool Test AidThe electronic service tool includes the test "Glow Plug Start Aid Override Test". This test will assist the analysis of the cold starting aid.Overview of the Glow Plug Start Aid Override TestThis glow plug start aid override test switches on the cold starting aid when the engine is not running. The glow plug start aid override test aids the analysis of the circuit for the glow plug start aid relay.
Illustration 1 g06366278
Schematic for the glow plug starting aid circuit
Not all connectors are shown. Refer to the appropriate Electrical Schematic.
Table 2
Troubleshooting Test Steps Values Results
1. Inspect Electrical Connectors and Wiring
A. Check that the fuses are not blown.
B. Inspect the terminals on the glow plug start aid relay and then inspect the connector on the flying lead from the relay. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
C. Inspect the bus bar for the glow plugs. Ensure that the nuts that secure the bus bar to each glow plug are tightened to a torque of 2 N m (17 lb in). Ensure that the bus bar is not shorted to the engine.
D. Check the harness for abrasion and pinch points from the glow plugs back to the ECM.
Note: Do not disconnect the ECM connector at this stage. The ECM can only be disconnected and reconnected 10 times before damage to the harness connector may occur.
Loose connection or damaged wire
Result: There is a fault in a connector or the wiring.
Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all the seals are properly in place and ensure that the connectors are correctly coupled.
Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.
Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points. The fuses are not blown. The bus bar is secured to the glow plugs and not shorted to ground.
Proceed to Test Step 2.
2. Check for Active Diagnostic Codes
A. Connect the electronic service tool to the diagnostic connector.
B. Turn the keyswitch to the ON position.
Note: Do not start the engine.
C. Use the electronic service tool to select the "Glow Plug Start Aid Override Test" to turn on the power for the glow plugs.
D. Check for an active or recently logged 676 diagnostic code.
Diagnostic codes
Result: No diagnostic codes are present.
There may be an intermittent fault in an electrical component between the ECM and the glow plugs. The problem may be inside an electrical connector. Refer to Troubleshooting, "Electrical Connector - Inspect" to identify intermittent faults.
There may be a fault in the glow plug switched power circuit. The ECM does not monitor the status of this condition.
Proceed to Test Step 7 to test this circuit.
Result: Diagnostic code 676-5 is active or recently logged.
Proceed to Test Step 3.
Result: Diagnostic code 676-6 is active or recently logged.
Proceed to Test Step 5.
3. Create a Short Circuit at the Relay Connector
A. Turn the keyswitch to the OFF position.
B. Remove the glow plug start aid relay.
C. Fabricate a jumper wire. Install the jumper wire between Test Point 1 and Test Point 2 on the harness connector for the glow plug relay. Refer to Illustration 1. Refer to the appropriate Electrical Schematic.
D. Turn the keyswitch to the ON position.
E. Use the electronic service tool to select the "Glow Plug Start Aid Override Test" to turn on the power for the glow plugs.
F. Use the electronic service tool to check for active diagnostic codes. Wait at least 30 seconds for activation of the diagnostic codes.
G. Turn the keyswitch to the OFF position and remove the jumper wire.
Diagnostic code
Result: A 676-6 diagnostic code is active with the jumper installed.
Install a replacement glow plug relay.
Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.
Result: The 676-5 diagnostic code is still active.
Proceed to Test Step 4.
4. Check the Wiring Between the ECM and the Relay for an Open Circuit
A. Verify