Diesel Engine Glow Plug Trouble Codes - keywords calibration circuit glowplug GPCM hard indicator LBZ LLY module multiple P064C P0671 P0672 P0673 P0674 P0675 P0676 P0677 P0678 program programming SES

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

A vehicle may be brought into the dealer with the SES light on and multiple cylinder glow plug DTCs set. Multiple glow plug DTCs may be caused by internal opens in the glow plugs. There are two different descriptions for an internal open in a glow plug. A fast open glow plug is a plug with an internal open circuitry, but no visual damage to the tip of the plug. A slow open glow plug is a plug that has internal open circuitry, and the tip of the plug is missing or damaged.

Complete the current SI diagnostics for any symptoms or DTCs found. If the diagnostics for P0671-P0678 led to a glow plug resistance of more than 1 ohm, replace all of the glow plugs. If any of the glow plug tips are missing, the cylinder head must be removed. All debris needs to be removed from the cylinder. When the tip of the glow plug enters the cylinder, engine damage may occur. Make any engine mechanical repairs as needed.

1. A loose battery feed connection at the starter, alternator, or the Glow Plug Control Module (GPCM) may induce glow plug concerns. When the starter, alternator, or GPCM battery feed circuit has a poor connection, the GPCM will sense a voltage fluctuation, and induce the GPCM to power up the glow plugs. Untimed GPCM cycling may cause glow plug concerns. Inspect the connections at the starter, alternator, and both ends of the battery feed cable to the GPCM. Connector C1 terminal 1 at the GPCM is a quick disconnect type of connector. Make sure terminal fit is clean and tight and the quick disconnect is seated properly. The source or main power feed location differs depending on the vehicle being serviced. On GMT800 C/K model trucks, the power feed stud is located in the Under Hood Bussed Electrical Center (UBEC). To access this power feed stud, the secondary UBEC cover has to be removed. On GMT610 "G" vans inspect the underhood junction block connection. On GMT560 4500/5500 trucks inspect the secondary fuse block connection.
2. There are other electrical scenarios that can induce glow plug concerns. If the glow plug system senses a certain electrical "noise" on the power feed, the glow plugs may also go open. This electrical "noise" may be induced by jump starting, disconnecting the batteries with the ignition in the ON position, or a battery charger being used during a module reprogramming event.
3. If the glowplug DTCs have set on a very low mileage vehicle (below 1000 miles) the glowplugs may have been damaged by the engine start up test conducted at the engine assembly plant.
4. Do not replace the GPCM for all 8 internal opened glow plugs. GPCMs have been returned and inspected with no problem found.
5. Complete all electrical circuit inspections and engine repairs as described above. After necessary repairs are completed, update the calibration in the GPCM. (See campaign 06522) Install the new GPCM software, and complete Fuel Injector Flow Rate Programming following SI procedures.

Note: Add-on remote starter or alarm kits must be removed before any glowplugs are replaced. Interruptions to normal starting procedures may induce glowplug concerns.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.