OBD-II Code U0106: Lost Communication With Glow Plug Control Module

What Does U0106 Mean?

U0106 means the Engine Control Unit (ECU) lost connection to the Glow Plug Control Module (GPCM). The GPCM controls the glow plugs that heat the engine's cylinders for cold starts. Without this link, the ECU cannot command the glow plugs to turn on, making cold starts extremely difficult.

Technical definition: Lost Communication With Glow Plug Control Module (GPCM). The Controller Area Network (CAN) bus detects a complete communication loss with the GPCM, or the GPCM is unresponsive to diagnostic requests.

Can I Drive With U0106?

Yes, But With Caution. Yes, but you will experience hard starting in cold weather. Ignoring the code causes a no-start condition, excessive battery and starter strain, and potential cylinder fuel wash. Fix the issue promptly to avoid being stranded.

Common Causes

• Faulty Wiring or Connectors (Very Common) — The wiring harness between the ECU and GPCM frequently suffers damage, corrosion, or loose connections. Connectors fill with moisture, pins break, and wires chafe in the harsh, high-heat diesel engine bay.
• Power or Ground Supply Issues (Common) — The GPCM requires a stable 12-volt power supply and a solid ground. A blown fuse, bad ground strap, or corroded battery terminals cause voltage drops that reset the module and trigger the code.
• Shared Circuit Interference (Especially on Deleted Trucks) (Common) — On modified or 'deleted' Ford Powerstroke trucks, the GPCM shares a power circuit with removed NOx sensors. Unplugged connectors suffer moisture intrusion, causing a short that blows the shared fuse and cuts power to the GPCM.
• Weak or Failing Vehicle Battery (Common) — A dying battery provides enough power to crank the engine but drops voltage low enough during startup to disrupt module communication, triggering U0106 even if the GPCM is perfectly fine.
• Failed Glow Plug Control Module (GPCM) (Common) — The module itself fails internally due to component burnout from high current spikes, solder joint fatigue from vibration and heat cycles, or water intrusion.
• Failed CAN Bus Termination Resistor (Less Common) — The CAN bus network requires a 120-ohm resistor at each end (totaling 60 ohms). If a resistor fails or its wiring breaks, it disrupts communication for multiple modules, including the GPCM.
• Corrupted GPCM Firmware or Software Glitches (Less Common) — An incomplete reprogramming attempt or severe electromagnetic interference corrupts the module's firmware, rendering the GPCM unable to communicate with the ECU.
• Faulty Engine Control Module (ECM/PCM) (Rare) — In rare instances, the main engine computer's CAN bus controller fails, making it unable to communicate with any modules. This triggers multiple 'U' codes simultaneously.

Symptoms

• Check Engine Light is On — The Malfunction Indicator Lamp (MIL) illuminates on your dashboard.
• Difficult or Extended Cranking to Start — The engine turns over for a longer time than usual before starting, especially when cold.
• No 'Wait to Start' or Glow Plug Light — The glow plug indicator light on the dashboard fails to turn on or flashes briefly.
• Excessive White or Grey Smoke on Startup — Unburned diesel fuel exits the exhaust as white or grey smoke immediately after a difficult start, clearing as the engine warms up.
• Rough Idle After Starting — When the engine starts, it runs roughly, idles unevenly, or stalls before reaching operating temperature.
• Vehicle Will Not Start — In colder temperatures or as the underlying problem worsens, the engine fails to start altogether.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Repairing Damaged Wiring or Cleaning Connectors — Parts: $5-$50, Labor: $150-$450, ~1.5 hr book time (Intermediate)
  Universal: OEM Varies by vehicle (Alt: {"brand": "Bostech", "number": "WH02065 (For Ford 2002-2010)"})
• Replacing a Blown Fuse or Bad Relay — Parts: $1-$20, Labor: $0-$60, ~0.2 hr book time (DIY)
• Sealing Unused Connectors on Modified Vehicles — Parts: $10-$30, Labor: $0-$75, ~0.3 hr book time (DIY)
• Replacing a Weak or Failing Battery — Parts: $150-$400, Labor: $25-$75, ~0.5 hr book time (DIY)
• Replacing the Glow Plug Control Module (GPCM) — Parts: $150-$900, Labor: $85-$300, ~1.0 hr book time (Professional)
  Ford 6.7L Powerstroke (2011-2019): OEM BC3Z-12B533-B (Alt: {"brand": "Dorman", "number": "904-917", "price_comparison": "Often less expensive than OEM"})
  GM 6.6L LMM Duramax (2007.5-2010): OEM 98022490 (Alt: {"brand": "ACDelco", "number": "98022490", "price_comparison": "OEM equivalent"})

Used vs. New Parts: Buying Guide

When a used part is worth it: A used GPCM from a reputable salvage yard is a cost-effective option for older, high-mileage vehicles where the cost of a new OEM part is prohibitive. It makes most sense if the part is easily accessible and does not require programming.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the part comes from a vehicle with a similar or lower mileage.
• Ensure the part number matches exactly, as even slight variations are incompatible.
• Inspect the used module's connectors for any signs of corrosion, bent pins, or heat damage before purchase.

Decision logic:

• If The vehicle manufacturer requires the new module to be programmed (common on Ford, GM) → Favor a new OEM or professionally remanufactured, pre-programmed module to avoid compatibility issues.
• If The vehicle is over 10 years old and the budget is very tight → A used part is a viable risk, but be prepared for the possibility of it failing sooner than a new part.
• If The GPCM is a known high-failure item for your specific model (e.g., LLY Duramax) → Favor a professionally remanufactured unit over a standard used one, as remanufacturers often correct original design flaws.

Warranty tradeoff: Used parts from salvage yards typically offer a 30-90 day warranty. New aftermarket parts often come with a 1-year to limited lifetime warranty. New OEM parts carry a 1-2 year warranty. Remanufactured modules often include a 1-year warranty.

Worst-case if a used part fails: $250-$1000

What Happens If You Wait — Timeline

1. 0-1 month: Check Engine Light is on. In mild weather, the truck starts normally. In cool weather (<50°F / 10°C), cranking time extends by a few seconds. No 'Wait to Start' light appears. (MPG impact: 0%% · Added cost: $0)
2. 1-3 months: Hard starting becomes consistent in any weather below 60°F / 15°C. The engine cranks for 5-10 seconds before starting, then runs rough with white/grey smoke for the first 30-60 seconds. Noticeable strain is placed on the starter and battery. (MPG impact: 0-1%% · Added cost: $50-$100)
3. 3-6 months: A no-start condition becomes likely, especially on cold mornings. The battery is too weak to sustain the long cranking needed to start. The starter motor is at high risk of burnout from overheating. Excessive unburned fuel during cranking begins to 'wash' oil from cylinder walls. (MPG impact: 1-2%% · Added cost: $400-$1100)
4. 6+ months: The vehicle is unreliable and leaves you stranded with a no-start condition. Repeated fuel washing causes accelerated wear on piston rings and cylinder liners, leading to loss of compression, oil consumption, and a need for major engine repairs. (MPG impact: N/A (vehicle likely won't start reliably)% · Added cost: $2000-$15000+)

Cost of Not Fixing It

• Immediate (0-1 month): Hard starting or no-start, especially in cold weather. Increased strain on the battery and starter motor from prolonged cranking. (Added cost: $200-$600)
• 1-6 months: Progressively worse starting issues, potentially leaving you stranded. Incomplete combustion during cold starts leads to fuel washing cylinder walls, diluting engine oil and causing premature wear. (Added cost: $500-$2000)
• 6+ months: Continued oil dilution damages piston rings and cylinder walls, leading to loss of compression and eventual engine failure. A persistent no-start condition becomes highly likely. (Added cost: $3000-$15000+)

Diagnosis Steps

1. Check for Other Codes
   Use an OBD-II scanner to read all stored trouble codes. Other 'U' (communication) or 'P' (powertrain) codes related to glow plugs (like P0380 or P0670) provide valuable clues. Multiple 'U' codes suggest a wider network problem.
   Tools: OBD-II Scanner (Beginner)
2. Inspect Fuses and Battery
   Check the GPCM fuse (labeled GPCM, Glow Plug, or Fuel Heater). Test the battery with a multimeter. A healthy battery reads above 12.4V when off and stays above 10.5V while cranking. A weak battery is a primary cause of communication codes.
   Tools: Multimeter, Owner's Manual (Beginner)
3. Visually Inspect the GPCM Wiring and Connectors
   Locate the GPCM. Inspect the wiring harness and connectors for corrosion, moisture, broken pins, pinched wires, or heat damage. Re-seating a loose connector often fixes the issue.
   Tools: Flashlight (Intermediate)
4. Test for Power and Ground at the GPCM
   Using a multimeter with the key on, verify battery voltage (12.0-12.8V) at the GPCM's main power pin. Check continuity between the ground pin and the negative battery terminal; resistance must be under 0.1 ohms.
   Tools: Multimeter, Vehicle-specific wiring diagram (Intermediate)
5. Perform a Voltage Drop Test (Advanced)
   With the key on, place one multimeter lead on the battery positive post and the other on the GPCM power wire. The reading must be under 0.5V. Repeat for the ground side. Higher readings indicate excessive circuit resistance.
   Tools: Multimeter, Vehicle-specific wiring diagram (Advanced)
6. Check CAN Bus Network Resistance (Advanced)
   With the battery disconnected, measure resistance between CAN High and CAN Low at the OBD-II port (pins 6 and 14). It must be approximately 60 ohms. A 120-ohm reading indicates an open circuit or missing resistor.
   Tools: Multimeter, Vehicle-specific wiring diagram (Advanced)
7. Check CAN Bus Voltages (Advanced)
   Reconnect the battery and turn the key 'On'. Measure CAN line voltages. CAN High (Pin 6) should be 2.5-3.5V, and CAN Low (Pin 14) should be 1.5-2.5V. Missing or identical voltages point to a short circuit.
   Tools: Multimeter, Vehicle-specific wiring diagram (Advanced)
8. Perform a Bidirectional Scan Tool Test
   Command the ECU to communicate with the GPCM using a professional scan tool. If the command fails despite verified wiring, power, and grounds, the GPCM has failed internally.
   Tools: Professional Bidirectional Scan Tool (Advanced)
9. Analyze Scan Tool Live Data (Advanced)
   Access the GPCM's live data stream. Look for PIDs related to GPCM status and voltage. If the tool reports 'No Communication' while other modules respond, it confirms an internal GPCM failure.
   Tools: Professional Bidirectional Scan Tool (Advanced)
10. Isolate the Module (Advanced)
    If multiple 'U' codes exist, disconnect modules one by one (starting with the GPCM) and re-check communication. If communication restores after unplugging the GPCM, it is shorting the entire CAN bus.
    Tools: OBD-II Scanner, Hand tools (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: Variable (The code often sets during a cold start attempt when the GPCM fails to respond. It also sets while driving if communication drops due to a wiring fault.)
• RPM: 0 (during pre-start) or 600-2500 (while driving) (Triggers during the 'key on, engine off' self-test or during normal driving if a connection becomes intermittent.)
• Engine Load: N/A (Engine load is not a primary factor for this communication-based code.)
• Vehicle Speed: 0 mph or any speed (The fault detects when the vehicle is stationary or in motion, depending on when the communication loss occurs.)

Related Codes

• P0380 — This code means 'Glow Plug/Heater Circuit 'A' Malfunction.' It often appears with U0106. **How to tell them apart:** U0106 indicates a total loss of communication; your scan tool cannot talk to the GPCM. P0380 means the ECU *can* talk to the GPCM, but the GPCM is reporting a fault in the glow plug circuit itself. If you have both, U0106 is the primary fault to diagnose.
• U0100 — 'Lost Communication With ECM/PCM 'A'.' If you see this code alongside U0106, it points to a more widespread network problem. **How to tell them apart:** U0106 is specific to the GPCM. U0100 means multiple modules have lost communication with the main engine computer. If U0100 is present, the root cause is a core network issue like a shorted CAN bus or a fault with the ECM itself. Diagnose U0100 first.
• P0670 — 'Glow Plug Module Control Circuit.' This code points directly to an electrical fault within the GPCM's control circuit. **How to tell them apart:** This code indicates the GPCM is online and communicating but has detected an internal error. U0106 means the GPCM is offline entirely. A U0106 points to a power, ground, or CAN bus wiring issue, while P0670 strongly suggests the module itself has failed internally.
• U010C — 'Lost Communication With Turbocharger Control Module.' On vehicles like the Ram Cummins, the turbo actuator and GPCM are on the same CAN bus circuit. A wiring issue (like a chafed harness) causes both codes to appear simultaneously, pointing to a shared circuit fault rather than individual module failures.

Climate & Environmental Factors

• Cold Weather: Cold weather makes the symptoms much more apparent. The GPCM and glow plugs are essential for cold starts, so a loss of communication results in extended cranking or a no-start condition primarily in low ambient temperatures. It also exacerbates issues with weak batteries, causing voltage drops that trigger communication codes.
• Humidity and Moisture: High humidity, heavy rain, or snow leads to moisture intrusion into electrical connectors. This is a direct cause of the U0106 code, leading to short circuits or corrosion on the GPCM connector, shared circuit connectors, or CAN bus junction points.
• Altitude: Thinner air at altitude requires a hotter combustion chamber for ignition, making the engine even more reliant on properly functioning glow plugs. A GPCM communication failure at high altitude makes a cold start significantly more difficult than at sea level.

How to Talk to a Mechanic About This Code

Say this: "I have a U0106 code on my truck and I'd like to schedule a diagnostic appointment. Please start by verifying the GPCM has proper power and ground, and check the CAN bus circuit integrity before recommending a module replacement. I'd also like to know if there are any technical service bulletins related to this code for my vehicle."

This signals to the service advisor that you understand the most common causes are electrical, not necessarily a failed module. It directs the technician to perform a proper diagnosis instead of jumping to the most expensive conclusion, potentially saving you hundreds in parts and labor.

Avoid saying:

• 'My check engine light is on, can you look at it?'
• 'My truck won't start right, just fix it.'
• 'I think I need a new glow plug computer.'

Questions to ask before authorizing the repair:

• Did you test for 12-volt power and a solid ground at the GPCM connector, and what were the exact readings?
• What was the ohm reading on the CAN bus network? Was it 60 ohms?
• If the GPCM module needs to be replaced, does the new part require programming and is that cost included in your quote?
• If the problem was a blown fuse, have you identified what caused the short circuit that blew it?

Where to Take It: Dealer vs Independent vs Chain

• Dealer:
  Best for: Vehicles still under powertrain or emissions warranty., Complex, manufacturer-specific issues that require programming., Known issues covered by a Technical Service Bulletin (TSB).
  Downsides: Typically the highest labor rates., May default to replacing an entire module or harness rather than performing a simpler wiring repair. (Typical cost: +40% vs. baseline)
• Independent Shop: Best fit. A reputable independent shop with strong diesel and electrical diagnostic skills is ideal for a U0106 code, as they are more likely to trace and repair a wiring fault, saving money over a full module replacement.
  Best for: Out-of-warranty vehicles where cost is a major factor., Shops that specialize in diesel or automotive electrical systems., Getting a second opinion on a costly dealer recommendation.
  Downsides: Quality and expertise vary widely; look for ASE certifications and good reviews., May not have access to the very latest manufacturer software for programming. (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid. This type of complex electrical diagnosis is not a good fit for most chain repair shops. The risk of misdiagnosis and unnecessary parts replacement is high.
  Best for: Simple, routine maintenance like oil changes, tires, and battery replacement.
  Downsides: Technicians often lack the specialized training for complex CAN bus and network diagnostics., High pressure to sell parts leads to replacing the GPCM without proper diagnosis. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the truck's private-party value, consider selling or trading it in.

• Car worth $15000, fix is $1200: Fix it. The repair cost is well below the threshold and is a reasonable investment to keep a valuable truck running.
• Car worth $8000, fix is $3500: Borderline. The cost is approaching 50% of the vehicle's value. Get a second opinion before proceeding, and consider any other needed repairs.
• Car worth $4000, fix is $2500: Walk away. The repair cost is over 60% of the truck's value. It is not a sound financial decision to proceed with this repair.

What Scan Tool You Need for This Code

Minimum: A scanner that reads manufacturer-specific codes and attempts to communicate with individual modules (like the GPCM).

A basic $20 code reader only shows the U0106 code. It cannot tell you if the GPCM is offline, if the CAN bus is faulty, or if other modules are also failing to communicate. For this code, you need a tool that performs a deeper network diagnosis.

Budget: BlueDriver Pro (~$99) — Confirms if the GPCM is communicating or not and checks for other module communication issues. Good for viewing live data like module voltage once communication is restored.

Mid-range: Innova 5610 / Foxwell NT510 Elite (~$150-350) — Offers bidirectional control to command the GPCM to respond, which is a critical diagnostic step. Reads manufacturer-specific codes and data, helping to distinguish between a network fault and a module fault.

Professional: Autel MaxiCOM MK808 / XTOOL D7 (~$450-700) — Provides full bidirectional control, comprehensive live data graphing, and network topology maps on some models. Performs the module programming that is often required after replacing a GPCM on Ford or GM vehicles.

Rent vs buy: For this code, a free rental from a parts store is not sufficient as it lacks the ability to test module communication. If you are a serious DIYer, buying a mid-range scanner is a worthwhile investment, as it is necessary for proper diagnosis and saves you money on future repairs.

How to Clear the Code After You Fix It

1. Reconnect battery if disconnected for the repair.
2. Use an OBD-II scan tool to formally clear the U0106 and any other related fault codes.
3. Perform a complete drive cycle to allow the vehicle's readiness monitors to run and confirm the fix.

Drive cycle (~20 minutes): Start the engine from cold and let it idle for 2-3 minutes. Drive in mixed city/highway traffic for 15-20 minutes, including a period of steady cruising at highway speeds (e.g., 55-65 mph) for at least 5 minutes. Allow the vehicle to cool down completely and repeat if all monitors have not set.

Readiness monitors affected: Comprehensive Component Monitor, Misfire Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Simply disconnecting the battery will not clear the code from the ECU's permanent memory and resets all readiness monitors to 'Not Ready'.
• The code returns immediately or on the next startup if the root cause (e.g., wiring short, bad module) was not correctly repaired.
• Not performing a full drive cycle leaves readiness monitors incomplete, leading to a failed emissions test even if the code is gone.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: A U0106 code triggers an automatic failure. The Check Engine Light being on fails the OBD-II portion of the Smog Check. All readiness monitors must be 'Ready' before a test can be passed after a repair.
• New York: The NY VIP includes an OBD-II scan. An active U0106 code causes an immediate failure of the emissions inspection.
• Texas: In counties requiring emissions testing, an illuminated Check Engine Light from a U0106 code results in a failed OBD-II test. The vehicle cannot be registered until the issue is fixed and the test is passed.

Most Commonly Affected Vehicles

• Ford F-250/F-350 Super Duty (6.7L Powerstroke) (2011-2019) — These trucks are known for this code, often caused by a blown fuse (#36) due to moisture in unplugged NOx sensor connectors on deleted trucks. The GPCM shares a power circuit with these sensors. The fix is to replace the fuse and seal the unused connectors.
• Chevrolet/GMC Silverado/Sierra 2500/3500 HD (LMM Duramax) (2007-2008) — A known issue per GM PI PIT4444 involves the high-speed GMLAN communication wires getting pinched or shorted between the truck bed and the frame, near the terminating resistor. This causes a loss of communication with multiple modules, including the GPCM.
• Isuzu N-Series (e.g., NPR) with 5.2L Diesel (2011-2018) — A manufacturer service bulletin (SB18-N-001A) points to water intrusion as a common cause. Water pools on the cylinder head and wicks into the glow plug harness, eventually reaching the GPCM connector. The official repair involves replacing harness terminals with updated sealed versions.
• Ram 2500/3500 (6.7L Cummins) (2013-2018) — These trucks experience U0106 due to wiring harness issues. The main harness rubs against the inner fender or other components, causing chafing and shorts on the CAN bus wires. The Totally Integrated Power Module (TIPM) is also a source of communication faults.
• Chevrolet/GMC Silverado/Sierra 2500/3500 HD (LLY Duramax) (2004-2005) — Internal failure of the GPCM is a very common issue on these specific models, often leading directly to a U0106 or P0670 code. Aftermarket replacement modules for the LLY are known to be unreliable; using a remanufactured OEM unit is recommended.
• BMW X5 35d, 335d (E70, E90) (2009-2013) — Failure of the glow plug control module is a common problem. It is located under the intake manifold, making replacement labor-intensive. A failing thermostat causes the glow plugs to cycle too often, leading to premature failure of the module.
• Volkswagen/Audi Jetta, Golf, A3 TDI (2009-2015) — The U0106 code on TDIs is frequently traced back to a faulty GPCM or issues with the wiring harness leading to it. The module itself is a common point of failure.
• Mercedes-Benz / Dodge / Freightliner Sprinter (NCV3) with 3.0L V6 (2007-2018) — Often caused by either an internal GPCM failure, a blown fuse, or oil/water ingress into the harness connectors. Check for power and ground at the module first, as fuse issues are common before condemning the module itself.

Manufacturer-Specific Notes

• GM / Chevrolet / GMC (Duramax): On 2007-2008 LMM models, check for pinched GMLAN communication wires between the truck box and frame near a terminating resistor. On 2004-2005 LLY engines, the GPCM itself is a very common failure point, and aftermarket replacements are notoriously unreliable, often causing a U0106 code out of the box. GM issued bulletin 23-NA-032 regarding the importance of cleaning glow plug bores with a reamer to prevent side-loading and premature failure of new plugs.
• Ford (Powerstroke): On deleted 6.7L trucks (2011-2019), the U0106 code is often caused by a blown fuse (check fuse #36 in the engine bay fuse box). This fuse blows because moisture gets into the now-unplugged NOx sensor connectors, which share a power circuit with the GPCM. The fix is to replace the fuse and properly seal the unused connectors with dielectric grease and caps.
• Isuzu: Per TSB SB18-N-001A, on 2011-2018 N-Series trucks, water pools on the cylinder head and wicks up the wiring harness into the GPCM connector, causing corrosion and communication loss. The official repair involves replacing harness terminals with updated sealed versions and applying dielectric grease.
• BMW: On M57 diesel engines (335d, X5 35d), the glow plug module is located under the intake manifold, making replacement a 4+ hour job. A common cause for premature module failure is a faulty engine thermostat that sticks open, causing the engine to run cool and forcing the glow plugs to cycle more frequently than designed, which burns out the module.

Real Owner Stories

2015 Ford F-350 6.7L (Deleted) with U0106 & P0100

Check engine light appeared with U0106 and P0100 (Mass Air Flow Sensor) codes after the truck's emissions systems were removed ('deleted'). The glow plug light would not come on.

Outcome: The owner located and replaced a blown 20A fuse (fuse #36 in the engine bay fuse box). They disconnected the old, unused NOx control modules under the truck which were shorting out and causing the fuse to blow. This restored power to the GPCM and MAF sensor, clearing both codes.

Lesson: On a modified (deleted) 6.7L Powerstroke, if U0106 appears with other codes like P0100, the first step is to check the specific fuse that powers the shared circuit before replacing any modules.

2004.5 Chevy Silverado 2500HD (LLY Duramax) with U0106

The check engine light came on and the glow plug light stayed on indefinitely. A scan revealed code U0106. The truck started and ran fine, but the code returned within minutes of being cleared.

Outcome: Replacing the GPCM with a new OEM Bosch unit resolved the issue. The U0106 code was cleared and did not return.

Lesson: For an LLY Duramax, an isolated U0106 code very commonly points to an internal failure of the GPCM itself. Aftermarket modules for this specific engine are known to be unreliable, so an OEM or remanufactured OEM unit is the recommended fix.

2017 Isuzu NPR with U0106

The truck's check engine light was on with code U0106. The vehicle experienced hard starting in colder weather.

Outcome: The fix involved cleaning the connectors with contact cleaner, applying dielectric grease, and replacing the original glow plug harness terminals with new, sealed pigtail versions to prevent future water entry. This resolved the communication fault.

Lesson: On Isuzu N-Series trucks, U0106 is frequently caused by a design issue where water pools on the cylinder head and gets into the harness. Follow the TSB to clean, seal, and update the harness terminals to prevent a recurring failure.

How to Prevent This Code From Triggering

• Periodically clean and protect key electrical connectors. (Every 2-3 years or after driving in harsh conditions (road salt, deep water).) — Applying dielectric grease to the GPCM connector, battery terminals, and main ground connections creates a barrier against moisture and oxygen, preventing the corrosion that causes high resistance and communication faults.
• Perform an annual battery load test. (Once per year, especially before winter.) — A weak battery that drops voltage excessively during cranking is a primary cause of random communication codes like U0106. An annual load test identifies a failing battery before it leaves you stranded.
• Seal any unused electrical connectors. (During any modification that involves unplugging a sensor (e.g., emissions delete).) — Open connectors in the engine bay collect moisture and road grime, leading to short circuits. This is the #1 cause of U0106 on deleted Ford trucks. Sealing them with dielectric grease and a cap prevents this.
• Ensure engine block and battery heaters are functional in cold climates. (Test before the first freeze of the season.) — Using a block heater reduces the strain on the entire starting system. It lessens the current draw on the battery, reduces the workload of the starter, and decreases the required 'on time' for glow plugs, extending the life of the GPCM.
• Avoid long-term idling. (Daily habit.) — Excessive idling leads to incomplete combustion and soot buildup. It does not efficiently warm up the engine, leading some drivers to cycle the key multiple times, which puts unnecessary stress on the GPCM and its relays over time.

Frequently Asked Questions

Can I fix a U0106 code myself?

Yes, if the cause is a blown fuse, loose connector, or bad battery. However, a failed module or complex wiring short requires advanced diagnostic tools. Stop DIYing and consult a shop if the new module requires VIN programming.

Will U0106 go away on its own?

No. This code indicates a hard fault in the communication network requiring diagnosis and repair. You must fix the underlying issue and clear the code with a scanner.

How much does it cost to fix U0106?

A diagnostic check costs $100-$200. Simple fixes like a fuse cost under $20, while replacing the GPCM ranges from $250 to $1,200 including parts and labor. Complex vehicles like the BMW X5 push costs toward the higher end due to labor.

What are the most common mistakes when diagnosing U0106?

The biggest mistake is replacing the GPCM without testing its power, ground, and communication wires. Many U0106 codes stem from a blown fuse, bad ground, or wiring issue. On modified trucks, failing to check shared circuits is a frequent oversight.

Can a bad battery cause a U0106 code?

Yes. A weak battery causes significant voltage drops during engine cranking. This disrupts communication between electronic modules and triggers a U0106 code, even if the GPCM works perfectly.

Does the new Glow Plug Control Module need to be programmed?

Yes, most modern diesel trucks (including GM and Ford) require programming the new GPCM to the vehicle's VIN. This requires a specialized bidirectional scan tool. Some remanufactured modules come pre-programmed, but verify before purchasing.

My glow plugs are good, so why do I have a U0106 code?

U0106 is a communication error, not a glow plug failure. The engine's main computer cannot talk to the module controlling the glow plugs. If the control module is offline due to a wiring issue or blown fuse, the system fails regardless of glow plug condition.

What does 'deleted' mean and why does it cause U0106 on my Ford?

A 'deleted' truck has its emissions control systems (like NOx sensors) physically removed. On 6.7L Powerstrokes, unplugged NOx sensor connectors share a power circuit with the GPCM. Moisture in these exposed connectors causes a short, blowing the shared fuse and triggering U0106.

Key Takeaways

• Code U0106 indicates the Engine Control Unit lost communication with the Glow Plug Control Module, causing extended 5-10 second crank times in weather below 60°F.
• Test the GPCM's 12-volt power supply and ground connections before spending $150-$900 on a replacement module, as wiring faults are the most common cause.
• Check engine bay fuse #36 immediately if you drive a deleted 2011-2019 Ford 6.7L Powerstroke, as moisture in unplugged emissions sensors frequently blows this shared GPCM fuse.
• Expect to hire a professional for the final repair step on modern GM and Ford diesels, as new GPCM units require VIN-specific programming with a bidirectional scan tool.