CAN network

U0106 — Lost Communication with Glow Plug Control Module

Severity: medium Drive with care, to a shop

What U0106 means

The engine control module talks to the glow plug control module (GPCM) over the CAN bus, sending pre-heat commands and receiving glow plug status. U0106 is set when the GPCM stops responding. The cause is usually power, ground, network wiring, or the module itself rather than the glow plugs.

Symptoms

  • Check Engine light on
  • Hard or prolonged starting, especially when cold
  • Rough idle after startup
  • Possible stalling or hesitation
  • Glow plug indicator behaving abnormally (not lighting, flashing, or staying on)
  • Other U-codes stored at the same time

Possible causes

  1. CAN bus fault between the ECM and the GPCM
  2. Poor power supply or weak ground at the glow plug module
  3. Corroded or damaged connectors and wiring
  4. Blown fuse in the module's power circuit
  5. Low system voltage (weak battery, bad terminals)
  6. Failed glow plug control module
  7. ECM software problem or fault (uncommon)

How to diagnose

  1. Scan all modules and note freeze frame data, looking for other U-codes or glow plug codes
  2. Test battery voltage and terminal condition, since low voltage can drop network communication
  3. Check the fuses and relays that feed the glow plug module per the wiring diagram
  4. Inspect the module connector and harness for corrosion, moisture, chafing, or broken wires
  5. Measure supply voltage and ground integrity at the module connector with the ignition on
  6. Test CAN-H and CAN-L for continuity, shorts, and proper bus resistance (about 60 ohms with power off)
  7. Measure each glow plug's resistance to rule out an open circuit
  8. Check for software updates before condemning the module or the ECM

Common fixes

  • Repair or replace damaged CAN wiring and connectors
  • Restore power and ground to the GPCM and replace blown fuses
  • Replace the glow plug control module
  • Replace any glow plugs found open-circuit
  • Reprogram or replace the ECM (rare)

Questions and answers

What does U0106 mean?

It means the engine computer lost communication with the glow plug control module over the CAN bus. The glow plugs may be fine; the issue is often power, wiring, or the module.

Can I drive with a U0106 code?

Short trips may be fine, especially in warm weather, but cold starts can become hard or impossible. Don't put off diagnosis or you may end up stranded.

Where should I start diagnosing U0106?

Check the battery, fuses, and the module's power and ground, then inspect the connectors and CAN wiring. Replace the module only after those checks pass.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.