BOLT-SOCKET HEAD 8C8729 - Caterpillar

This procedure covers the following diagnostic code:Use this procedure if there is a suspected fault in the glow plug start aid circuit or the glow plugs.
Table 1
Diagnostic Trouble Code for the Glow Plug Starting Aid    
J1939 Code    Code Description    Comments    
676-6     Engine Glow Plug Relay : Current Above Normal     The Electronic Control Module (ECM) detects the following conditions:
The engine is not cranking.
The ECM has been powered for at least one second.
There is a high current condition (short circuit) in the glow plug start aid relay circuit for more than 2 seconds.
If equipped, the warning light will come on. The diagnostic code will be logged. An ECM that was previously blank will require a total of 2 hours of operation before the diagnostic code will be logged.
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 in order 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 isolator switch 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 temperatureIf the glow plugs are required, then the ECM will activate the glow plug and glow plug earth relays for a controlled period. While the glow plug relays are 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 in order 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 Test The 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 g03590326
Schematic for the glow plug starting aid circuit
Illustration 2 g03590329
View of the pin locations on the P1 connector for the glow plug circuit (12) Glow plug earth relay control (20) Glow plug relay control (59) Actuator drive return
Table 2
Troubleshooting Test Steps    Values    Results    
1. Inspect Electrical