U0106

Lost Communication With Glow Plug Control Module

U0106 is a generic OBD-II network diagnostic trouble code: Lost Communication With Glow Plug Control Module. It is logged by the engine control unit when the glow monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
U0106
Group
Network
System
Glow
Severity
Warning (MIL on)
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What U0106 means

U0106 is set when a primary control module, typically the PCM or engine control module (ECM), loses CAN bus communication with the glow plug control module (GPCM). The GPCM is a dedicated controller found on diesel engines that manages the heating of each cylinder's glow plug for cold-start assistance and post-start heating cycles. It reports individual glow plug status and fault information back to the PCM over the network.

With communication lost, the PCM cannot monitor glow plug health, receive post-heating cycle status, or coordinate the glow plug strategy with fuel injection timing. While the GPCM may continue operating on its last programmed strategy, the PCM will set U0106 and potentially disable advanced glow plug diagnostics. Cold-start performance is most affected, particularly in sub-zero temperatures.

Diagnosis should include verifying the GPCM power and ground supply, inspecting the CAN bus wiring to the module (often located on or near the engine valve cover), and checking for corrosion or heat damage at the connector. GPCMs on high-heat engines are prone to failure from thermal cycling.

Common causes

Most-frequently reported root causes when U0106 is logged.

  • 1
    Failed GPCM due to heat damage from proximity to the engine.
  • 2
    Open or short in the CAN bus wiring harness near the GPCM.
  • 3
    Blown power supply fuse for the GPCM.
  • 4
    Corroded or heat-damaged connector at the GPCM.
  • 5
    Loose or high-resistance ground connection at the GPCM.
  • 6
    Damaged CAN bus termination causing network signal degradation.
  • 7
    GPCM over-current protection tripping due to shorted glow plug heater circuit.

Symptoms drivers notice

Hard cold starting in low ambient temperatures.
MIL illuminated; glow plug warning lamp may flash at startup.
Individual glow plug fault codes may not be retrievable while U0106 is active.
Possible white smoke on cold start due to incomplete combustion.
Scan tool cannot communicate with the GPCM.

How to diagnose U0106

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs and check for glow plug individual fault codes in addition to U0106.
  2. 2
    Verify GPCM power supply voltage and ground circuit integrity at the module connector.
  3. 3
    Inspect the GPCM connector and adjacent wiring for heat damage, corrosion, or fraying.
  4. 4
    Test CAN bus differential signal at the GPCM connector with an oscilloscope.
  5. 5
    Attempt to establish scan tool communication with the GPCM via a module scan.
  6. 6
    Check the glow plug high-current wiring for shorts that may have overloaded the GPCM.
  7. 7
    Replace the GPCM if internal failure is confirmed after all external checks pass.

Related network codes

Frequently asked questions

Will U0106 prevent the engine from starting?

In mild weather the engine will usually start without glow plugs. In cold climates, loss of glow plug control can cause no-start or extended cranking.

Can shorted glow plugs damage the GPCM?

Yes. A shorted glow plug draws excessive current, which can trigger the GPCM protection circuit or damage the module's internal power electronics.

Is the GPCM serviceable separately from the glow plug wiring harness?

On most vehicles the GPCM is a standalone replaceable module, though its mounting location near high-heat areas often means the harness connector should be replaced simultaneously if corroded.

Does U0106 affect emissions test results?

U0106 will illuminate the MIL and will cause the vehicle to fail an OBD-II emissions inspection in jurisdictions that check for active MIL-on codes.

Disabling U0106 in software

RaceTune can permanently disable U0106 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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