BIT-END 7D9999 - Caterpillar

System Operation Description: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 Codes for the Glow Plug Start Aid Relay Circuit    
J1939 Code    Description    Notes    
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.    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 intake manifold air temperature in order to decide if the glow plugs need to be switched ON. If 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 in order to indicate the "Wait To Start" period.The engine is equipped with ether injection. Glow plugs are used for temperatures that are between 5° C (41° F) and −25 °C (−13 °F). If the ambient temperature is below −25 °C (−13 °F), the glow plugs are disabled and ether injection is used."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 This 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 g02252573
Typical schematic for the glow plug starting aid circuit
Illustration