U0106 medium Severity

U0106: Lost Communication With Glow Plug Control Module

Can cause hard starting, rough idle, prolonged cranking, particularly in diesel engines; may illuminate check engine light but vehicle may still run

Overview

OBD-II U0106 indicates a loss of communication between the Engine Control Module (ECM/PCM) and the Glow Plug Control Module (GPCM) over the CAN bus, often due to wiring, connector, power/ground issues, or module failure.

Common Symptoms

  • Check Engine or MIL illuminated
  • Hard or prolonged starting, especially in cold conditions
  • Rough idle after startup
  • Possible engine stall or hesitation
  • Glow plug indicator abnormalities

Most Common Causes

CAN bus communication fault between ECM and GPCM high

Open, short, or resistance issues in CAN+ or CAN- circuits can prevent module communication.

Poor power supply or ground to Glow Plug Control Module medium

Blown fuse, weak battery, or compromised ground strap can interrupt module operation.

Corroded or damaged connectors/wiring medium

Environmental exposure can cause corrosion at harness connectors, especially in diesel glow plug circuits.

Faulty Glow Plug Control Module (GPCM) medium

Internal module failure due to moisture or component burnout can stop communication even if wiring is intact.

ECM/PCM communication fault or software issue low

Rare but possible; includes software glitches or faulty control module.

Diagnostic Steps

  1. Perform a full OBD-II scan and record all stored codes.
    Expected: U0106 present, possibly with related communication or power codes.
    Interpretation: Establish baseline; other codes can guide root cause.
  2. Visually inspect wiring and connectors between ECM and GPCM.
    Expected: No broken, chafed, corroded wires or loose pins.
    Interpretation: Damage indicates likely wiring/connector repair before further testing.
  3. Check power and ground at GPCM with multimeter.
    Expected: 12.0–12.8 V on power pins, ground <0.1 Ω.
    Interpretation: Poor power/ground suggests fuse, battery, or ground strap issues.
  4. Test CAN bus signals at the module with key on engine off.
    Expected: Approximately 2.6 V on CAN+ and 2.4 V on CAN- fluctuating.
    Interpretation: Abnormal voltages indicate CAN bus circuit issues.
  5. If wiring and power/ground check good, bench test or substitute known-good GPCM.
    Expected: GPCM responds correctly to communication.
    Interpretation: Failure confirms module fault.

Repair Solutions

Repair or replace damaged CAN bus wiring/connectors medium
Estimated Cost: $50 - $300

Correct wiring integrity generally resolves communication error.

Restore proper power and ground to GPCM easy
Estimated Cost: $10 - $100

Replace fuses, tighten grounds, or battery service as needed.

Replace faulty Glow Plug Control Module (GPCM) medium
Estimated Cost: $500 - $1200

VIN-matched replacement and programming may be required on some vehicles.

ECM/PCM reprogram or replacement (rare) hard
Estimated Cost: $800 - $1500

Only after exhaustive wiring and module verification.

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Assuming glow plugs themselves are faulty
  • Replacing ECM/PCM without verifying wiring and connectors
  • Ignoring related communication codes before diagnosing U0106

Frequently Asked Questions

What does a U0106 diagnostic trouble code signify?

The U0106 code stands for Lost Communication With Glow Plug Control Module. This generally indicates an issue with the Engine Mechanical system.

Can U0106 cause engine damage?

This is a medium priority issue. Can cause hard starting, rough idle, prolonged cranking, particularly in diesel engines; may illuminate check engine light but vehicle may still run

How do I know if I have code U0106?

Common symptoms include: Check Engine or MIL illuminated, Hard or prolonged starting, especially in cold conditions, Rough idle after startup. You might also notice the Check Engine Light is on.

What causes the U0106 code?

The most common causes are: CAN bus communication fault between ECM and GPCM, Poor power supply or ground to Glow Plug Control Module, Corroded or damaged connectors/wiring.

Is U0106 expensive to fix?

It depends on what needs to be fixed. Restore proper power and ground to GPCM repairs are cheaper (~$100), while ECM/PCM reprogram or replacement (rare) repairs are on the higher end (~$1500).

Is the U0106 code specific to BMW?

The U0106 code is a generic powertrain code, meaning it applies to almost all makes and models, such as Honda, Toyota, VW, Ford, and Chevy.

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