U0106

Universal

Lost Communication With Glow Plug Control Module

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The glow plug control module manages preheating for a diesel engine, helping it start and run smoothly when cold. U0106 means another vehicle control system has detected that it cannot communicate with that module. A communication fault does not by itself prove the module has failed; starting or running effects may be more noticeable in cold conditions, and some vehicles may show no obvious symptoms.

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⚠️ Before You Begin (Safety First)

This code alone does not usually mean the vehicle must be stopped immediately. If the engine is difficult to start, runs very roughly, stalls, or a warning indicates a separate serious fault, avoid driving until it is assessed. Keep clear of hot engine parts and moving components during checks.

Common Symptoms

  • The code may be stored with no noticeable change in how the vehicle runs.
  • Hard starting when the engine is cold may occur if glow plug preheating is unavailable.
  • Rough running or increased exhaust smoke shortly after a cold start may occur if the engine does not preheat effectively.
  • A warning light or message may appear, depending on the vehicle.
  • Other communication-related codes or missing module data may accompany the fault.

Common Causes

  • Loss of power or ground to the glow plug control module can prevent it from communicating.
  • Loose, damaged, corroded, or contaminated module connectors or wiring can interrupt communication.
  • A fault in the vehicle communication network or its wiring can prevent messages from reaching the module.
  • Low or unstable vehicle battery voltage may disrupt module operation or communication.
  • The glow plug control module may have an internal fault, but this should be considered after checking its power, ground, connections, and network path.

Diagnostic Steps

  1. Record the symptoms and note whether they occur mainly during cold starts; this helps establish whether the preheating function may be affected.
  2. Check the battery terminals for looseness or visible corrosion and have the battery condition checked if starting is weak, because low voltage can affect control-module communication.
  3. With the ignition off, visually inspect accessible wiring and connectors associated with the glow plug control module for damage, looseness, corrosion, or moisture. Do not force connectors or work near hot or moving parts.
  4. Check the vehicle owner's manual for any relevant fuses and inspect them safely; use the specified replacement type if a fuse is blown, and seek diagnosis if it blows again.
  5. If a suitable scan tool is available, record codes from all modules before clearing anything. Multiple communication or voltage codes can help identify a broader electrical or network issue.
  6. If the fault returns or wiring and fuse checks do not explain it, arrange diagnosis using service information for the exact vehicle rather than replacing the module based on this code alone.

When to Call a Professional

Use a scan tool capable of checking all modules to confirm which systems report the communication loss and whether other network or voltage codes are present. Check the glow plug control module's power, ground, connectors, and wiring, then assess the vehicle network using model-, year-, and engine-specific service information. Replace a module only after its supplies, connections, and communication path have been checked.

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Commonly Asked Questions

Does U0106 prove the glow plug control module is bad?

No. It indicates a loss of communication with the module. Power, ground, connectors, wiring, battery voltage, or the vehicle communication network can also cause the condition.

Can I drive with U0106?

The code alone does not necessarily require an immediate stop, but cold starting or engine operation may be affected. Do not continue driving if the engine stalls, runs very roughly, or another serious warning appears.

Why might there be no symptoms?

The fault may be intermittent, or the engine may start and run acceptably in current conditions even though a communication problem has been recorded.

What should be checked before replacing the module?

Check for related codes, battery condition, module power and ground, connector and wiring condition, and communication-network faults using vehicle-specific service information.

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