OBD-II Code U0105: Lost Communication With Fuel Injector Control Module

What Does U0105 Mean?

Code U0105 means the Powertrain Control Module (PCM) lost connection with the Fuel Injector Control Module (FICM). The FICM controls fuel delivery timing and volume in diesel engines. Without this communication link, the engine cannot run and will not start.

Technical definition: The official SAE/OBD-II definition is "Lost Communication With Fuel Injector Control Module". This indicates the FICM stopped responding to network requests on the Controller Area Network (CAN) bus.

Can I Drive With U0105?

No — Do Not Drive. Do not drive the vehicle. The engine will likely stall unexpectedly in traffic, creating a severe collision risk and leaving you stranded.

Common Causes

• Faulty Fuel Injector Control Module (FICM) (Very Common) — The FICM is the most frequent point of failure. Internal components, specifically the power supply and logic board, fail from extreme heat, engine vibration, and voltage drops.
• Weak Batteries or Failing Alternator (Common) — The FICM requires stable voltage. Weak batteries or a failing alternator provide inconsistent power, which permanently damages the FICM's internal circuits and severs communication.
• Damaged Wiring, Connectors, or Grounds (Common) — The CAN bus wires connecting the FICM to the vehicle's network frequently chafe against engine components. Loose connector pins, moisture corrosion, or a frayed chassis ground wire also break the connection.
• Blown FICM Fuses or Relays (Common) — The FICM relies on specific high-amperage fuses and relays for main and logic power. A blown fuse or faulty relay cuts all power to the module instantly.
• Aftermarket Modifications or Incorrect Reassembly (Less Common) — Aftermarket performance tuners cause software conflicts that drop the FICM from the network. Additionally, failing to fully seat wiring harnesses after an engine repair triggers this code.
• Faulty PCM or Corrupted CAN Bus (Rare) — A failing Powertrain Control Module (PCM) or another shorted module on the CAN bus floods the network with noise, blocking the FICM's signal.

Symptoms

• Engine will not start (Crank, no start) — The engine cranks normally but refuses to fire because the injectors receive no command to deliver fuel.
• No injector 'buzz' sound — On diesel trucks, turning the key produces a distinct 2-3 second buzzing sound from the injectors. If the FICM is offline, this sound disappears completely.
• Engine stalls unexpectedly — The engine starts and runs briefly, then dies suddenly while idling or driving. This happens more frequently as the engine reaches operating temperature.
• Rough running and misfiring — The engine idles poorly, shakes violently, and sputters due to erratic fuel delivery commands.
• Check Engine Light is on — The Malfunction Indicator Lamp illuminates immediately when communication drops.

Diagnostic Flowchart

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

Common Fixes & Costs

• Replace the Fuel Injector Control Module (FICM) — Parts: $300-$900, Labor: $150-$300, ~2.0 hr book time (Intermediate)
  Ford F-250/F-350 6.0L (2004.5-2007): OEM 4C3Z12B599ABRM (Alt: {"brand": "Alliant Power", "part_number": "AP65123"}, {"brand": "BD Diesel", "part_number": "1059700-A"})
  Chevy/GMC Silverado/Sierra 6.6L LLY (2004.5-2005): OEM 97303751 (Alt: {"brand": "Bosch", "part_number": "0281011134"})
• Repair FICM (Mail-in Service) — Parts: $200-$450, Labor: $0-$150, ~1.5 hr book time (DIY)
• Replace Alternator and Batteries — Parts: $400-$800, Labor: $150-$300, ~1.5 hr book time (Intermediate)
• Replace Blown Fuses or Relays — Parts: $5-$30, Labor: $0-$50, ~0.2 hr book time (DIY)
• Repair Damaged Wiring or Connectors — Parts: $20-$100, Labor: $200-$600, ~3.0 hr book time (Professional)

Used vs. New Parts: Buying Guide

When a used part is worth it: A used FICM from a salvage yard only makes sense for an older, high-mileage truck on a strict budget. Used electronics carry no lifespan guarantee and are highly risky for this specific part.

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

Donor quality checklist:

• Match the OEM part number exactly.
• Inspect all connector pins for green corrosion or burning.
• Verify the donor vehicle was not junked for electrical fires or flood damage.

Decision logic:

• If The vehicle is a Ford 6.0L or GM Duramax → Buy a high-quality remanufactured unit with an upgraded power supply. The failure rate of original used units is too high to risk.
• If Budget is the primary concern → Use a mail-in repair service for your original module rather than buying a used junkyard part.
• If You want maximum reliability → Purchase a new OEM or premium aftermarket FICM with a lifetime warranty.

Warranty tradeoff: Used parts offer 30-day warranties covering only the part. Remanufactured units from specialists offer 1-year to lifetime warranties. New OEM parts carry a 2-year warranty.

Worst-case if a used part fails: $600 (Cost of a failed used part, repeat labor, and towing fees)

What Happens If You Wait — Timeline

1. 0-4 weeks: Intermittent fault. The code appears after a hard cold start, but the truck runs normally. The FICM momentarily loses voltage but recovers. (MPG impact: 0%% · Added cost: $0)
2. 1-3 months: The truck stalls unexpectedly once a week but restarts. Cold starts require longer cranking. The FICM's internal power supply is actively degrading. (MPG impact: 5%% · Added cost: $150 (Potential towing fee))
3. 3-6 months: The truck stalls daily when hot and requires a cool-down period to restart. The engine misfires heavily. The FICM fails completely at operating temperature. (MPG impact: 15%% · Added cost: $400 (Strained batteries and starter motor))
4. 6+ months: Permanent crank-no-start condition. The FICM is completely dead. Voltage spikes from a bad alternator may have damaged the PCM. (MPG impact: N/A% · Added cost: $1500 (FICM replacement plus potential PCM damage))

Cost of Not Fixing It

• Immediate: The vehicle stalls in traffic or refuses to start, creating a severe safety hazard. (Added cost: $150-$400 (Tow truck fee))
• Short-Term (days to weeks): Repeatedly cranking a non-starting engine destroys the starter motor and drains the batteries past the point of recovery. (Added cost: $400-$800 (New batteries and starter motor))
• Long-Term (weeks to months): A failing alternator sending voltage spikes through the network permanently damages other sensitive control modules. (Added cost: $500-$2000 (Replacement PCM or TCM))

Diagnosis Steps

1. Check Batteries and Charging System
   Test your batteries and alternator first. A voltage reading below 12.4V with the engine off, or below 10.5V while cranking, starves the FICM. The alternator must output 13.7-14.7V when running.
   Tools: Digital Multimeter (Beginner)
2. Inspect FICM Fuses and Relays
   Locate the FICM, Injector Driver Module, or EDU fuses in the power distribution box. Pull them out and inspect for broken internal wires or burnt relay contacts. Replace any blown fuses immediately.
   Tools: Owner's Manual, Fuse Puller (Beginner)
3. Analyze Scan Tool Live Data
   Connect an advanced scan tool and monitor FICM PIDs. Check FICM_LP (Logic Power) and FICM_MP (Main Power), which must match battery voltage. Verify FICM_SYNC reads '1' or 'Yes'. If SYNC is '0', the module is offline.
   Tools: Advanced Scan Tool (Advanced)
4. Test FICM Output Voltage
   On a Ford 6.0L or GM Duramax, check the FICM's output voltage (FICM_V) via scan tool or back-probing. It must read 47-49V with the key on and never drop below 45V while cranking. A drop below 45V confirms a dead FICM power supply.
   Tools: Advanced Scan Tool or Digital Multimeter (Advanced)
5. Perform a Visual Inspection and 'Wiggle Test'
   Inspect the wiring harness leading to the FICM for rub marks, especially over valve covers or alternator brackets. With the key on, gently wiggle the harness and connectors. If you hear the injectors click or the scan tool loses connection, you found a wiring short.
   Tools: Flashlight (Beginner)
6. Check Power and Ground at the FICM
   Disconnect the FICM. Use a multimeter to verify 12.0V+ at the power pins on the harness connector. Test the ground pins for continuity to the chassis; resistance must be near 0 ohms.
   Tools: Digital Multimeter, Vehicle-specific Wiring Diagram (Intermediate)
7. Test CAN Bus Network Resistance
   Disconnect the negative battery cable. Measure resistance between CAN High and CAN Low pins at the diagnostic port (pins 6 and 14). A healthy network reads exactly 60 ohms. 120 ohms indicates an open circuit; 0 ohms indicates a short.
   Tools: Digital Multimeter (Advanced)
8. Analyze CAN Bus Signal with an Oscilloscope
   Connect a dual-channel oscilloscope to the CAN High and CAN Low wires. You must see a clean square wave pattern toggling between 1.5V and 3.5V. A flat line or excessive noise confirms a corrupted network.
   Tools: Dual-Channel Oscilloscope, Wiring Diagram (Professional)

When This Code Triggers (Freeze-Frame Conditions)

• Engine State: Key On, Engine Off or Cranking (The code sets when the PCM attempts to initialize communication with the FICM during startup and receives no response.)
• Engine Coolant Temp: 170-200°F (The fault frequently occurs when the engine bay is fully heat-soaked, confirming a thermal failure of the FICM logic board.)
• Vehicle Speed: 0 mph or highway speeds (Occurs at startup (0 mph) or causes a sudden stall at highway speeds, indicating a hard module failure or vibration-induced wiring short.)
• Battery Voltage: <12.0V or fluctuating (Low system voltage during cranking is the primary trigger for FICM communication loss.)

Related Codes

• P0611 — FICM Performance. U0105 means the FICM is completely offline. P0611 means the FICM is online but detects internal low voltage. Seeing both guarantees a failed FICM.
• U0100 — Lost Communication with ECM/PCM. Diagnose U0100 first. If the main engine computer is offline, the FICM cannot communicate with it.
• U0306 — Software Incompatibility with FICM. Appears immediately after installing a replacement FICM, indicating the new module requires VIN programming.
• P0201-P0208 — Injector Circuit Malfunction. If these cylinder-specific codes appear alongside U0105, the FICM logic board has failed and cannot control individual injectors.

Climate & Environmental Factors

• High Heat: The FICM mounts directly on top of the engine. Extreme thermal cycling degrades internal circuit boards and fractures solder joints, causing premature failure.
• Cold Weather: Freezing temperatures severely drop battery cranking voltage. The FICM requires high voltage to operate; repeated cold starts with weak batteries destroy the power supply.
• Humidity and Moisture: Water intrusion corrodes the FICM's multi-pin connectors and chassis ground points, increasing electrical resistance and severing communication.

How to Talk to a Mechanic About This Code

Say this: "I have a U0105 code and a no-start condition. Before replacing the FICM, please perform a full load test on the batteries and alternator, and check the FICM's power, ground, and output voltage."

This directs the shop to check foundational electrical issues first, preventing them from installing a $900 module into a truck with a bad alternator that will instantly destroy the new part.

Avoid saying:

• My truck won't start, just fix it.
• I think I need a new FICM, can you give me a price?
• Just clear the code and see if it runs.

Questions to ask before authorizing the repair:

• Did you load-test the batteries and check alternator output under load?
• What was the exact FICM voltage reading at key-on and while cranking?
• Did you inspect the wiring harness at the known chafe spots?
• Does the replacement FICM include an upgraded power supply and a warranty?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: A safe but expensive choice. Best used if independent shops cannot locate a complex CAN bus short.
  Best for: Vehicles under powertrain warranty, When you require guaranteed OEM parts and a nationwide warranty
  Downsides: Highest labor rates, Will default to expensive module replacement rather than repairing wiring (Typical cost: +50% vs. baseline)
• Independent Shop: The best option, provided you choose a dedicated diesel specialist. Stop DIY and tow to a specialist if you verify good battery voltage but lack the scan tool to test FICM output.
  Best for: Out-of-warranty diesel trucks, Shops specializing in diesel performance or electrical diagnostics
  Downsides: General mechanics lack the specific scan tools and knowledge for diesel network issues. (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid completely. Chain shops cannot properly diagnose CAN bus communication faults.
  Best for: Tires, batteries, and oil changes
  Downsides: Technicians lack advanced diagnostic training and OE-level scan tools. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the total estimated repair cost exceeds 40% of your truck's current private-party market value, seriously consider selling the vehicle.

• Car worth $10000, fix is $1200: Fix it. The repair cost is well within a reasonable threshold.
• Car worth $8000, fix is $2500: Borderline. Get a second opinion to confirm the diagnosis before proceeding.
• Car worth $4500, fix is $2000: Walk away. The repair cost approaches half the vehicle's value.

What Scan Tool You Need for This Code

Minimum: A scanner capable of reading manufacturer-specific live data PIDs, specifically FICM Main Voltage, Logic Power, and Sync status.

A $20 code reader only confirms the U0105 code exists. Without live data to view FICM voltage, you are guessing and will likely replace the wrong part.

Budget: FORScan (with OBD adapter) / BlueDriver Pro (~$25-120) — Accesses and graphs essential PIDs like FICM Voltage and Sync. This is the absolute minimum required to diagnose a failing power supply.

Mid-range: Foxwell NT510 Elite (~$150-200) — Provides deep access to all vehicle modules with robust live data graphing. Excellent for serious DIYers.

Professional: Autel MaxiCOM MK808 (~$400-600) — Offers full bidirectional control to command modules and run active tests. Essential for finding complex network-wide communication shorts.

Rent vs buy: Buy. Free loaner tools from auto parts stores cannot read the live data required to diagnose a U0105 code.

How to Clear the Code After You Fix It

1. Reconnect the vehicle's battery if disconnected during repair.
2. Use an OBD-II scan tool to erase the DTCs from the PCM's memory.
3. Perform a complete drive cycle to reset readiness monitors.

Drive cycle (~20 minutes): Start the engine cold and idle for 3 minutes. Drive in mixed city/highway conditions, including steady-state cruising and stop-and-go traffic, for 20 minutes to reach full operating temperature.

Readiness monitors affected: Comprehensive Component Monitor (CCM), Misfire Monitor

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

Watch out for:

• Disconnecting the battery clears the dashboard light but resets all readiness monitors to 'Not Ready', guaranteeing an emissions failure.
• The code returns immediately if you replace the FICM without fixing the underlying bad alternator.
• Failing to drive the vehicle at highway speeds prevents the Comprehensive Component Monitor from running.

Will This Fail Emissions / State Inspection?

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

• California: An active U0105 code causes an automatic smog check failure. The Check Engine Light must be off and monitors set to 'Ready'.
• New York: Results in an automatic failure of the NYS OBD-II emissions inspection.
• Texas: An illuminated Check Engine Light and stored U0105 code automatically fails the OBD-II portion of the state inspection.

Most Commonly Affected Vehicles

• Ford F-250/F-350/Excursion 6.0L Power Stroke (2003-2007) — Extremely common. The FICM power supply fails due to low battery voltage. The wiring harness frequently chafes near the valve covers.
• Chevrolet / GMC Silverado / Sierra 6.6L Duramax (LLY & LB7) (2001-2005) — A primary cause for a crank-no-start condition. The wiring harness passing over the alternator bracket is a notorious chafing point.
• Hummer H1 Alpha 6.6L Duramax (2006-2006) — Uses the exact same Duramax LLY engine and FICM system as GM trucks, suffering identical failures.
• Dodge Ram 2500/3500 6.7L Cummins (2007-2018) — Less common. Communication issues here usually stem from a failed VGT turbo actuator disrupting the CAN bus, rather than the FICM itself.
• Hyundai Genesis (2009-2014) — Refers to a communication error between the ECM and the Injector Driver Box (IDB).
• Honda Accord / Fit / Civic (2007-2023) — Often a secondary code triggered by a fault in an unrelated system, like a wheel speed sensor, crashing the CAN bus.
• Toyota Yaris / Vitz / RAV4 (2006-2012) — Highly misleading on Toyotas. It usually indicates a loss of communication with the Power Steering or Transmission Control Module, not the fuel system.
• Subaru Impreza / Forester / Outback (2008-2024) — Frequently appears as a 'ghost' code after a battery disconnect. Ignore it unless accompanied by drivability symptoms and a primary P-code.

Manufacturer-Specific Notes

• Ford: On 6.0L engines, low battery voltage guarantees FICM failure. Always test the alternator before replacing the module. TSB 09-24-03 outlines updated diagnostic procedures.
• General Motors (GM): On 2004.5-2005 LLY Duramax engines, the harness passing over the alternator bracket chafes and shorts the communication wires. Always check the 'EDU' fuse in the underhood box.
• Toyota: Code U0105 is notoriously inaccurate on Toyotas. It frequently triggers due to Power Steering or Transmission module faults, leading mechanics to misdiagnose the fuel system.
• Subaru: U-codes store as historical faults after minor voltage drops during startup. If the car drives normally, clear the code; it rarely indicates a hard failure.

Real Owner Stories

2004 Ford F-350 6.0L at 146K miles

Truck died suddenly at highway speeds when warm. It restarted after cooling down. Code U0105 was present.

What they tried:

1. Replaced the FICM relay with no change.
2. Swapped in a known-good FICM, which temporarily fixed the issue.
3. Sent the original FICM for mail-in repair. After reinstalling, the truck died again within 500 feet.

Outcome: The root cause was an intermittent wiring short in the main harness that destroyed the repaired FICM immediately upon installation.

Lesson: Never assume the module is the only problem. An underlying electrical short will instantly destroy a brand new or repaired FICM. Always perform a wiggle test on the harness.

2005 GMC Sierra 2500HD 6.6L LLY Duramax

Experienced an intermittent crank-no-start condition with code U0105.

What they tried:

1. Checked all fuses and grounds.
2. Swapped a spare FICM, which allowed the truck to start but run poorly.
3. Replaced the fuel pressure relief valve spring, which masked the issue for 5 weeks.

Outcome: The issue was a chafed wire in the harness passing over the alternator bracket, causing intermittent communication loss.

Lesson: On Duramax engines, thoroughly inspect the wiring harness near the alternator bracket before condemning the FICM or fuel system components.

2006 Toyota Yaris

Vehicle shuddered and misfired. Scan revealed code U0105.

What they tried:

1. Began tearing down the engine to inspect fuel injector wiring based on the code definition.

Outcome: A technician confirmed U0105 is a misleading 'ghost' code on Toyotas, triggered by a failing Transmission Control Module disrupting the network.

Lesson: On Japanese imports, U0105 rarely points to the fuel system. Always diagnose primary 'P' codes first and look for faults in other major modules.

How to Prevent This Code From Triggering

• Perform Annual Battery and Alternator Health Checks (Once per year) — Low voltage is the primary killer of FICMs. Load-testing batteries and verifying alternator output prevents voltage drops that destroy the module's power supply.
• Protect Wiring Harnesses in Chafe-Prone Areas (During any engine service) — Adding split-loom tubing or Tesa tape to harnesses crossing valve covers or metal brackets prevents vibration-induced electrical shorts.
• Upgrade to a High-Output Alternator (When replacing a failed stock alternator) — High-output alternators provide stable amperage at low RPMs, ensuring the FICM receives consistent 14V+ power under heavy electrical loads.

Frequently Asked Questions

Can I drive my truck with a U0105 code?

No, it is not safe to drive. The engine stalls without warning, creating a severe collision risk in traffic. You also risk being stranded when the engine refuses to restart.

Will a U0105 code clear itself?

It is highly unlikely. This code indicates a hard fault in the communication network or a failed module. You must repair the underlying problem before the code clears permanently.

What is a CAN bus and how does it relate to U0105?

The CAN bus is your vehicle's internal computer network. It consists of two wires that electronic modules use to share data. Code U0105 means the FICM stopped transmitting on this network.

Is it better to repair or replace my FICM?

Both are viable options depending on your budget and timeline. A full replacement is faster but costs up to $900. Mail-in repair services cost around $300 and often include upgraded components to prevent future failures.

My truck starts cold but dies when warm. Is this U0105?

Yes, this is a classic symptom of a failing FICM. Internal solder joints expand and break connection as the module heats up. Once the engine cools, the connection restores temporarily.

What is the most common mistake when diagnosing U0105?

The biggest mistake is replacing the FICM without testing the charging system. Always verify battery voltage and alternator output first. Installing a new FICM into a truck with a bad alternator will destroy the new module.

My scanner shows U0105, but the truck runs fine. What should I do?

This indicates an intermittent or historical network glitch. Clear the code and perform a test drive. If it returns, you have a developing wiring or connector problem that requires diagnosis.

Can a bad ground cause a U0105 code?

Absolutely. The FICM requires a solid chassis ground to operate and communicate. A loose or corroded ground wire causes intermittent communication loss and directly triggers code U0105.

Key Takeaways

• Code U0105 indicates the Fuel Injector Control Module (FICM) stopped communicating with the engine computer, immediately causing a crank-no-start condition or unexpected stalling.
• A failed FICM is the root cause in over 80% of U0105 cases on Ford 6.0L Power Stroke and GM Duramax diesel engines.
• Test your batteries and alternator before replacing the FICM, as voltage drops below 12.0V permanently damage the module's internal power supply.
• Never drive a vehicle with an active U0105 code, as the engine will eventually stall in traffic and require a $150+ tow to a repair shop.