U0106 is a network communication code indicating the Powertrain Control Module (PCM) has lost communication with the Glow Plug Control Module (GPCM). This module manages the heating cycle of glow plugs in diesel engines for cold starting. The code is set when the PCM cannot receive a response from the GPCM over the CAN bus.
The GPCM itself is the most common failure point; internal circuit failure prevents CAN communication.
Damaged, chafed, or corroded wiring between the PCM and GPCM, or at the module connector.
Loose, corroded, or oxidized connectors at the GPCM or PCM causing intermittent communication loss.
A blown fuse in the glow plug circuit power supply can prevent module operation and communication.
If equipped, a failed glow plug relay can starve the module of power, causing communication loss.
Rarely, the PCM itself may have a CAN communication fault, but this should be diagnosed after all other causes are ruled out.
Yes, but with limitations. In warm weather the engine may start normally since glow plugs are not needed. In cold weather, hard starting or no-start is likely. The code indicates a communication fault, not an immediate safety issue, but the underlying cause should be diagnosed.
Rarely. While a failed PCM could cause this code, it is the least likely cause. Technicians commonly report customers being told to replace the PCM unnecessarily. Always diagnose the glow plug control module and its wiring first before considering PCM replacement.
Yes, the GPCM is a separate module and can be replaced individually in most applications. It is typically located on the engine or in the engine bay fuse/relay box.
U0106 is most common on diesel-powered vehicles from manufacturers that use a separate glow plug control module, including various GM, Ford, and Dodge diesel applications. Check for manufacturer-specific TSBs.