U0106 – Lost Communication With Glow Plug Control Module

System: Network | Standard: ISO/SAE Controlled | Fault type: General

Definition source: SAE J2012/J2012DA (industry standard)

DTC U0106 indicates that one or more control modules on the vehicle network have detected a loss of communication with the Glow Plug Control Module. This is a network (communication) fault, not a direct confirmation that glow plugs, relays, or wiring are mechanically failed. The vehicle sets this code when expected message traffic is missing, invalid, or not acknowledged for a calibrated time, and the exact criteria and affected functions can vary by vehicle. Because communication architecture, module locations, and power/ground routing differ, always verify wiring diagrams, connector views, and pinpoint tests in the appropriate service information before replacing parts.

What Does U0106 Mean?

U0106 – Lost Communication With Glow Plug Control Module means the vehicle has detected that the Glow Plug Control Module is not communicating properly over the network. Under SAE J2012 DTC structuring, a “U” code identifies a network-related fault, and this specific entry points to missing communication with the module responsible for controlling or managing glow plug operation. In practice, the fault is typically set when other modules (often the engine controller) no longer receive the required network messages from the Glow Plug Control Module, receive messages that are not usable, or cannot establish/maintain a network link as expected.

Quick Reference

  • Subsystem: Vehicle network communication path to/from the Glow Plug Control Module.
  • Common triggers: Module power/ground loss, open/high resistance in network wiring, short to power/ground on network circuits, disconnected/loose connectors, or a non-responsive module.
  • Likely root-cause buckets: Wiring/connector faults; power/ground feed issues; network bus faults; module internal failure; configuration/software issues (varies by vehicle).
  • Severity: Typically moderate; may cause hard starting or extended cranking in cold conditions and may illuminate warning indicators; severity increases if the vehicle experiences no-start or multiple communication codes.
  • First checks: Verify battery state and main fuses; scan for multiple network DTCs; check if the Glow Plug Control Module is detectable by a scan tool; inspect connectors and harness routing for damage.
  • Common mistakes: Replacing glow plugs or the control module without confirming network integrity and module power/ground; ignoring related U-codes that indicate a broader bus problem.

Theory of Operation

The Glow Plug Control Module typically receives requests and operating context over the vehicle network, then commands glow plug heating according to engine conditions. Other modules expect periodic network messages (status, confirmation, fault states, or readiness information) from the Glow Plug Control Module so they can coordinate starting strategy and diagnostics. When communication is healthy, the module powers up, joins the network, and transmits/receives messages at defined intervals.

U0106 is set when a supervising module determines that required communication from the Glow Plug Control Module is absent or not valid. This can occur if the module loses its power or ground, if network wiring is open/shorted/noisy, if connector pin fit is poor, or if the module itself stops communicating. The code identifies a communication loss event; it does not by itself prove which physical component is at fault.

Symptoms

  • Warning light illumination related to engine or system faults, often accompanied by a stored network code.
  • Hard start or extended cranking, especially when preheating assistance is needed (varies by vehicle and conditions).
  • No start in cases where the starting strategy depends on glow plug control confirmation (varies by vehicle).
  • Reduced function such as inhibited glow plug operation or a default strategy due to missing module status.
  • Multiple codes including additional network communication DTCs if the network issue affects more than one module.
  • Intermittent issue where the vehicle starts normally sometimes but sets U0106 under vibration, temperature change, or moisture exposure.

Common Causes

  • Open circuit, high resistance, or intermittent connection in the network communication wiring between the Glow Plug Control Module and the rest of the vehicle network
  • Poor connector contact (loose fit, spread terminals, corrosion, contamination) at the Glow Plug Control Module or at an in-line network junction/connector
  • Short-to-ground or short-to-power affecting the network communication circuit(s), disrupting message traffic
  • Loss of power feed(s) to the Glow Plug Control Module (blown fuse, failed relay, open in power supply wiring)
  • Ground circuit problem for the Glow Plug Control Module (loose ground fastener, damaged ground wire, high resistance at ground point)
  • Module not waking up or resetting due to unstable supply/ground (momentary dropouts) causing repeated loss of communication events
  • Network-wide issue where another module or wiring fault is pulling the bus down, preventing communication with multiple modules
  • Glow Plug Control Module internal fault (hardware failure) after power/ground and network integrity are verified

Diagnosis Steps

Tools typically needed include a scan tool capable of full-network module discovery, DTC retrieval from multiple modules, and live-data logging; a digital multimeter for voltage-drop and continuity checks; and access to vehicle-specific wiring diagrams and connector views. Basic backprobing tools and terminal inspection aids are helpful to check pin fit and connector condition without causing damage.

  1. Confirm the complaint and scan the full network. Record U0106 and all other stored/pending codes from every module. Note which modules are “not responding” versus those that communicate normally; this helps determine whether the issue is isolated to the Glow Plug Control Module or is a broader network problem.
  2. Capture freeze-frame and network status data. Save available freeze-frame, last-fault details, and communication status indicators (varies by vehicle). If your scan tool supports it, start a short live-data log that includes network health/status and any “module alive” or “message counter” parameters.
  3. Check for current versus history behavior. Clear codes (if allowed by service information) and cycle the key/ignition as required. Re-scan to see if U0106 resets immediately, returns after a drive cycle, or only appears intermittently. An immediate return often points to a hard power/ground/network fault; an intermittent return often points to connector/terminal issues or harness movement sensitivity.
  4. Verify the module is present on the network. Attempt direct communication with the Glow Plug Control Module using the scan tool. If the scan tool cannot establish communication, proceed to power/ground and network physical checks. If it does communicate, compare module information and review any companion codes that suggest low voltage, reset events, or network errors (varies by vehicle).
  5. Inspect fuses, relays, and power distribution for the module. Using the wiring diagram, identify all power feeds that supply the Glow Plug Control Module (constant and switched, as applicable). Check the relevant fuses and relays under load where possible. If a fuse is open, do not replace repeatedly without checking for a short or downstream fault.
  6. Perform voltage-drop testing on power and ground circuits. With the circuit powered as designed (ignition state per service info), test voltage drop across the module power feed path and across the ground path. Excessive drop indicates high resistance in wiring, connectors, relay contacts, or ground points. Repair the high-resistance point rather than condemning the module.
  7. Inspect the Glow Plug Control Module connectors and terminals. Key off and follow service information precautions. Disconnect the module connectors and check for bent pins, backed-out terminals, corrosion/contamination, damaged seals, or evidence of overheating. Confirm terminal tension/pin fit using appropriate methods for the connector type. Repair terminal issues and ensure connectors fully seat and lock.
  8. Check network wiring integrity to the module. Using wiring diagrams, identify the network communication circuit(s) at the module connector. Inspect the harness routing for pinch points, chafing, prior repairs, and areas where the harness can move. Perform continuity checks only when the circuit is properly isolated per service information; otherwise prioritize resistance/short checks that won’t risk module damage.
  9. Test for shorts affecting the network. With the module disconnected as needed, check for short-to-ground or short-to-power on the network communication circuit(s) using the multimeter and the procedure specified by service information. If a short is present, isolate by disconnecting intermediate connectors/junctions to locate the faulted harness segment.
  10. Wiggle test while monitoring. Reconnect as appropriate and monitor scan tool communication status and live-data logging while gently flexing the harness near the module, along the suspected routing, and at junction connectors. If communication drops in/out with movement, focus on that area for broken conductors, poor splices, or intermittent terminal contact.
  11. Rule out a network-wide bus issue. If multiple modules show communication-related codes or intermittent “no response,” inspect common network splices/junctions and the main network trunk. A fault elsewhere on the network can prevent communication with the Glow Plug Control Module even if its local wiring is intact.
  12. Confirm the repair with a repeat scan and road test. After repairs, clear codes, run the ignition cycles/drive cycle required by service information, and confirm the Glow Plug Control Module communicates consistently. Recheck for U0106 and any related network or voltage codes and verify they do not return.

Professional tip: Treat U0106 as a communication loss symptom first, not an automatic module failure. If the Glow Plug Control Module is offline, the fastest path is usually to prove module power and ground integrity with voltage-drop testing, then prove the network wiring and terminal fit at the module connector. Intermittent U0106 is often caused by harness movement sensitivity or poor terminal tension, so a logged road test plus a controlled wiggle test can be more revealing than static checks.

Need network wiring diagrams and module connector views?

Communication stop and network faults require module connector pinouts, bus wiring routes, and power/ground diagrams. A repair manual helps you trace the exact circuit path before replacing any ECU.

Factory repair manual access for U0106

Check repair manual access

Possible Fixes & Repair Costs

Repair costs for U0106 vary widely because the root cause can range from a simple connector issue to a network fault or module-level problem. Total cost depends on diagnostic time, required parts, access difficulty, and whether wiring repairs or module setup procedures are needed.

  • Restore power and ground: Repair blown fuses, faulty relays (if used), weak feeds, or poor grounds supplying the glow plug control module.
  • Repair wiring/connector faults: Fix opens, shorts, high resistance, corrosion, pin fit issues, or damaged terminals on the network and module circuits.
  • Network repairs: Correct faults on the communication bus (varies by vehicle) such as shorts between bus lines, shorts to power/ground, or poor splice/junction integrity.
  • Clean and secure connections: Service module connectors and nearby harness routing; ensure proper seating, locking, and strain relief.
  • Module replacement (only after testing): Replace the glow plug control module only if power/ground and network circuits test good and communication remains lost.
  • Configuration/setup as required: Perform any required programming, setup, or relearn steps after module replacement (varies by vehicle and tool capability).

Can I Still Drive With U0106?

You may be able to drive with U0106, but it depends on how the vehicle responds to the loss of communication with the glow plug control module. Starting difficulty, reduced power, warning messages, or other network-related faults can occur, and cold starts may be especially affected. If the vehicle exhibits a no-start, repeated stalling, multiple critical warning indicators, or enters a severe reduced-power mode, do not continue driving; have it diagnosed and repaired to prevent being stranded and to avoid compounding network or electrical issues.

What Happens If You Ignore U0106?

Ignoring U0106 can lead to recurring hard starts or no-start conditions (often more noticeable in colder conditions), increased strain on the electrical system during repeated start attempts, and additional communication faults as the underlying issue worsens. If the cause is a harness, connector, or power/ground problem, ongoing vibration and heat can increase resistance or intermittency, making the problem more frequent and harder to diagnose later.

Compare nearby lost glow trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • U017D – Lost Communication With Control Module “M”
  • U017C – Lost Communication With Control Module “L”
  • U017B – Lost Communication With Control Module “K”
  • U017A – Lost Communication With Control Module “J”
  • U0179 – Lost Communication With Control Module “I”
  • U0178 – Lost Communication With Control Module “H”

Key Takeaways

  • U0106 is a network communication fault: It indicates lost communication with the glow plug control module, not a confirmed glow plug failure.
  • Power/ground checks come first: A module that is unpowered or poorly grounded cannot communicate.
  • Wiring and connector issues are common: Opens, corrosion, pin fit problems, and harness damage can mimic module failure.
  • Intermittent faults need logging: Capturing when communication drops helps pinpoint a loose connection or harness movement issue.
  • Replace parts only after circuit verification: Confirm network integrity and module supplies before considering module replacement.

Vehicles Commonly Affected by U0106

  • Vehicles equipped with a glow plug control module: Systems using an external controller are more likely to set this code when communication is lost.
  • Vehicles with extensive networked modules: More modules and gateways can increase the impact of a single communication interruption.
  • High-mileage vehicles: Age-related connector pin tension loss and harness wear can contribute to intermittent communication loss.
  • Vehicles exposed to harsh environments: Moisture, road contaminants, and heat cycling can accelerate terminal corrosion and wiring degradation.
  • Vehicles with recent electrical repairs: Harness routing changes, incomplete connector seating, or ground disturbances can trigger communication faults.
  • Vehicles with battery or charging concerns: Low system voltage events can interrupt module operation and network messaging.
  • Vehicles with underbody/engine-bay harness stress: Areas with frequent movement or abrasion risk can develop opens or intermittent shorts.

FAQ

Does U0106 mean the glow plugs are bad?

No. U0106 means the vehicle detected lost communication with the glow plug control module. Glow plug condition is separate and cannot be concluded from this code alone; communication, power/ground, and network integrity must be verified first.

What should I check first for U0106?

Start with module power and ground integrity, then inspect the module connector and nearby harness for damage or poor pin fit. After that, verify the communication network circuits for opens, shorts, or high resistance using appropriate test methods and service information.

Can a weak battery cause U0106?

It can contribute. Low voltage events can cause modules to reset or drop off the network, which may be detected as lost communication. However, the code can also be caused by wiring faults or a module issue, so testing is required to confirm the root cause.

Why does U0106 come and go?

Intermittent U0106 often points to a loose connector, marginal terminal tension, corrosion, or a harness fault that opens/closes with vibration, heat, or engine movement. Capturing freeze-frame data and logging network/module status while performing a careful wiggle test can help isolate the intermittent point.

Do I need to replace the glow plug control module for U0106?

Not automatically. Replace the module only after verifying that its power and ground are correct and stable, the network circuits are intact, and connectors/harnesses are in good condition. If replacement is required, additional setup or programming may be needed depending on vehicle design and tooling.

If you’re unsure where the glow plug control module is located or which network circuits it uses, consult the correct service information for your vehicle to avoid misidentifying connectors or testing the wrong circuits.