U0106 — Data bus: glow plug control module – no communication #

Note: The wording of this code may vary depending on the vehicle manufacturer.

• Glow Plug Control Module ‘A’ – Lost Communication (Ford, GM, FCA)
• Lost Communication With Glow Plug Control Module (VW/Audi, Mercedes-Benz, Nissan)
• CAN Bus: No Signal from Glow Plug Control Unit (BMW, Peugeot)

Code summary for U0106 #

The U0106 diagnostic trouble code (DTC) signals a loss of communication between the engine control module (ECM) and the glow plug control module via the vehicle’s main data bus, also known as the CAN bus (Controller Area Network). The glow plug control module is responsible for managing the operation of glow plugs, which preheat the combustion chambers in diesel engines for optimal cold starting. When the ECM can’t exchange messages with this module, it flags U0106. This code typically indicates an electronic or wiring fault, but could also be caused by module failure or power/ground issues. Left unresolved, U0106 can affect diesel engine performance, especially during cold starts.

Common symptoms for code U0106 #

When a U0106 code is stored, you might notice the engine struggles or fails to start in cold weather. The check engine light (CEL) will usually illuminate, and you may experience rough idling or increased exhaust smoke at start-up. Sometimes, there may be no obvious symptoms apart from the warning light.

• Check engine light (CEL) illuminated
• Hard or no start, especially in cold weather
• Rough idle after start-up
• Increased white/gray smoke on cold start
• Reduced engine performance until warm
• Glow plug indicator light may flash or not illuminate

Probable causes for code U0106 (in order of likelihood) #

Several issues can trigger a U0106 code. The most common cause is an open or short in the CAN bus circuit between the ECM and the glow plug control module. Other likely causes include power or ground loss to the module, connector corrosion, or an outright failure of the glow plug control module itself.

1. CAN bus wiring faults (open/short circuits, damaged wires)
2. Poor electrical connections at glow plug control module or ECM (corrosion, loose pins)
3. Faulty glow plug control module
4. Loss of power or ground to the glow plug control module
5. ECM internal fault (rare)

Step-by-step diagnostic for U0106 #

Diagnosing a U0106 code requires a systematic approach, starting with the basics and moving toward more complex checks. The aim is to isolate whether the fault lies in the wiring, connections, the glow plug control module, or the ECM itself.

• Verify the code with a scan tool and check for additional related codes.
• Inspect the glow plug control module and ECM connectors for corrosion, bent pins, or loose fit.
• Check CAN bus wiring continuity and resistance between the ECM and glow plug control module using a multimeter.
• Ensure the glow plug control module is receiving proper battery power and ground.
• Test for short to power or ground in the CAN lines.
• If wiring and power/ground are good, try clearing the code and cycling the ignition to see if it returns.
• Substitute the glow plug control module with a known good unit (if available and appropriate).
• As a last resort, consider ECM diagnosis or replacement if all other components test good.

Possible repairs for U0106 #

Once the root cause is identified, repairs for U0106 target the faulty link in the communication chain. Many cases are resolved by addressing wiring or connector issues rather than component replacement.

• Repair or replace damaged CAN bus wiring between ECM and glow plug control module
• Clean or repair corroded or loose connectors at both modules
• Restore proper power or ground supply to the glow plug control module
• Replace the glow plug control module if it is confirmed faulty
• Replace the ECM only after verifying all other possibilities

Is it safe to drive with code U0106? #

Driving with a U0106 code is not recommended, especially in cold weather. While the engine may still start and run under mild conditions, failure of the glow plug system can lead to hard starting, increased emissions, and potential engine damage from unburned fuel. If the vehicle is used in a cold climate or relies on proper cold starts, address this code promptly to avoid getting stranded or causing further damage.

Vehicles most commonly affected by U0106 #

The U0106 code is most frequently encountered on modern diesel vehicles with electronically controlled glow plug systems. Many OEMs use this module-based architecture, but it is particularly common in certain brands and models.

• Ford (F-Series Super Duty, Transit, Focus diesel)
• Chevrolet/GMC (Duramax-equipped trucks and vans)
• Dodge/Ram (Cummins diesel models)
• Volkswagen and Audi TDI models
• Mercedes-Benz Sprinter and BlueTEC diesels
• Nissan (Titan XD diesel, Navara)
• BMW diesel models
• Peugeot/Citroën HDi models

Common mistakes & best practices for U0106 #

When diagnosing and repairing U0106, skipping essential checks or replacing expensive modules prematurely are frequent errors. A thorough process saves time and money.

• Assuming the glow plug control module is faulty without checking wiring and connectors
• Overlooking simple power/ground faults to the module
• Not inspecting for corrosion or water ingress at connectors
• Forgetting to clear codes and road test after repairs
• Best practice: Always verify wiring integrity and connector condition before replacing any modules

Quick FAQ for U0106 #

Here are answers to the most common questions about U0106:

• Q: Can I just clear the code and keep driving?
  A: Clearing the code may temporarily turn off the warning light, but if the underlying issue isn’t fixed, the problem will return and may worsen—especially in cold weather.
• Q: Does this code mean my glow plugs are bad?
  A: Not necessarily. This code points to a communication issue with the control module, not a direct glow plug failure. The glow plugs themselves may still be fine.
• Q: Is this repair expensive?
  A: Many U0106 repairs involve wiring or connector fixes, which are generally less expensive than module or ECM replacements. However, costs vary depending on the root cause and labor time.