OBD-II trouble code
U0106: Lost Communication with Glow Plug Control Module
A module on the network can no longer hear from the glow plug control module. Usually a power, ground, or wiring fault — and because this diesel module preheats the cylinders, you may get hard cold starts, rough cold running, and white startup smoke.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $800
- DIY difficulty
- Shop recommended
What does U0106 mean?
U0106 is set when another module on the vehicle's communication network — usually the engine computer — stops receiving messages from the glow plug control module. This module is found on diesel engines, where it powers the glow plugs that heat each cylinder to help the fuel ignite during cold starts and warm-up. It takes commands from the engine computer about how long and how hard to run the glow plugs and reports their status back over the network. When the network loses contact with that module, U0106 records the dropout.
The causes follow the familiar communication-code pattern. The glow plug control module may have lost power or ground through a blown fuse, corroded ground, or failed relay — and because it switches high current to the glow plugs, its power connections work hard and are a common failure point. The CAN wiring or connector at the module can be damaged or corroded, often from engine-bay heat and vibration. The module's internal communication circuitry can fail, or another module on the bus can disrupt communication for everyone. Low system voltage from a weak battery can also cause intermittent dropouts.
The symptoms are mostly tied to cold operation. The engine may be hard to start when cold, run rough or shake for the first minute, and produce white smoke until it warms up; the glow plug warning light may stay on or flash. The check engine light comes on, often with companion glow-plug or preheat codes. Once the engine is warm it generally runs normally, so the vehicle is usually driveable — but repeated hard cold starts are tough on the starter and battery, and the underlying fault should be addressed before cold weather makes it worse.
Common causes
- Blown power or ground fuse for the glow plug control module
- Corroded or loose ground at the module
- Damaged or burned high-current power connection at the module
- Damaged CAN wiring to the glow plug control module
- Corroded or backed-out terminals at the module connector
- Failed internal communication circuitry in the module
- Another module on the bus disrupting network communication
- Low system voltage from a weak battery or charging fault
Symptoms
- Hard starting when the engine is cold
- Rough running or shaking for the first minute after a cold start
- White smoke from the exhaust until the engine warms up
- Glow plug warning light on or flashing
- Check engine light on, often with glow-plug or preheat codes
- Scan tool can't communicate with the glow plug control module specifically
- Symptoms may be intermittent with a marginal connection
Diagnostic steps
- 1.Scan all modules; confirm the glow plug control module is the one that's unreachable while others respond.
- 2.Check the module's power and ground fuses, the high-current feed, and any relevant relays.
- 3.Inspect the module ground and connector for corrosion, looseness, heat damage, and burned terminals.
- 4.Measure CAN-High and CAN-Low at the module connector (rest near 2.5 volts) and verify continuity back to the bus.
- 5.Test the battery and charging system, since low voltage can cause intermittent communication loss.
- 6.If power, ground, and wiring are good but the module still won't communicate, the module itself is the likely failure and will need replacement and programming.
Repair cost
$100 – $800
A blown fuse, corroded ground, or connector repair is the cheapest fix at $100-$300 once located. Wiring or burned-terminal repair runs $200-$600. Diagnostic time commonly adds $150-$300. Glow plug control module replacement is the most expensive outcome at $250-$800 including programming, and is a last resort after cheaper causes are ruled out. Note that bad glow plugs themselves are a separate repair from the control module.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.