There may be several glow plug DTCs set on some 2024-2026 Silverado 2500HD/3500HD and Sierra 2500HD/3500HD trucks equipped with the 6.6L Duramax diesel engine (RPO L5P).
DTCs may include:
- P066A (Cylinder 1 Glow Plug Control Circuit Low)
- P066C (Cylinder 2 Glow Plug Control Circuit Low)
- P066E (Cylinder 3 Glow Plug Control Circuit Low)
- P067A (Cylinder 4 Glow Plug Control Circuit Low)
- P067C (Cylinder 5 Glow Plug Control Circuit Low)
- P067E (Cylinder 6 Glow Plug Control Circuit Low)
- P068C (Cylinder 7 Glow Plug Control Circuit Low)
- P068E (Cylinder 8 Glow Plug Control Circuit Low)
These DTCs may be caused by a blown fuse or a bent terminal in the X950D 55-way (Engine Wiring Harness Chassis-to-Engine Wiring Harness) connector.
If fuse F5 (F5BA) is open, it will result in cylinders 1, 4, 6 and 7 all setting DTCs simultaneously. If fuse F6 (F6BA) is open, it will result in cylinders 2,3,5 and 8 all setting DTCs simultaneously.
Terminal damage in the X950D 55-way connector also will result in individual DTCs setting.
TIP: Do not replace or disturb any glow plugs before checking the Battery Distribution Unit (BDU) Fuse Assembly (Fig. 1) for a bent terminal in the X950D 55-way connector.
Fig. 1
Check for Blown Fuse
Check for 12 volts at the BDU ring terminal while wiggling the cable. (Fig. 2) Some blown fuse conditions will intermittently make contact. If fuse contact is intermittent or the fuse is blown, it may be necessary to replace the BDU assembly.
Fig. 2
Separate the X950D connector by disengaging the red CPA and squeezing the corners of the connector. Look for bent terminals in the X950D connector (Fig. 3) that may result in individual Glow Plug Control Circuit DTCs P0671, P0672, P0673, P0674, P0675, P0676, P0677 and/or P0678 setting.
Fig. 3
Refer to Bulletin #26-NA-077 for additional information.
– Thanks to Larry Yaw
