U0100: How to Diagnose & Fix — Lost Communication with ECM/PCM
25 vehicles · 11 makes · $80-$3,500 repair
How to diagnose and fix U0100: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Ford Fusion · 2011–2013
NHTSA recall 15V340 covers 2011-2013 Ford Fusion (and Lincoln MKZ) without the 3.5L engine. An intermittent electrical connection in the steering gear can cause sudden loss of electric power steering assist while driving. Owners notice heavier steering effort especially at low speeds, increasing crash risk. Dealers check the Power Steering Control Module (PSCM) for DTCs; if any loss-of-assist codes are stored, the steering gear is replaced free. Note: 2010 Fusions had the same parts but were excluded from the recall — feds closed the probe without expanding scope. 2010-owner symptoms are real but uncovered by recall.
Common Symptoms
- Power steering warning message on dashboard
- Steering becomes heavy or requires extra force
- Intermittent loss of power steering assist
- Steering wheel off-center after loss of assist
- Clunking or grinding from steering column area
- Complete loss of power steering (requires significant force to turn)
- Steering assist comes and goes unpredictably
- Check engine light or power steering fault code stored
How to Fix
Check if your vehicle is covered under Ford recall (2011-2012 Fusion/MKZ power steering failure recall - free repair). For non-recall vehicles, the electric power steering rack must be replaced as a complete unit since the motor and control electronics are integrated. RepairPal estimates $1,958-3,362 installed. Remanufactured racks from PWR Steer or Cardone are available at $800-1,500, significantly cheaper than new OEM ($2,000+). Have the alignment performed after rack replacement.
Sources for this issue (1)
Jaguar S-TYPE · 2000–2008
The S-TYPE is notorious for electrical gremlins caused by moisture ingress into control modules and poor CAN bus connections. Phantom warning lights, inoperative features, and intermittent faults across multiple systems are common and difficult to diagnose without dealer-level equipment.
Common Symptoms
- Multiple warning lights illuminated simultaneously
- Windows or locks operating erratically
- Instrument cluster errors or flickering
- Intermittent no-start condition
- Features working one day and not the next
How to Fix
Check all module locations for moisture ingress, particularly the driver footwell and trunk. Clean and reseal all CAN bus connectors with dielectric grease. Reprogram affected modules with the latest software. Replace the 12V battery if it is over 4 years old.
Owner tips & cautions
- TipBuy an iCarsoft i930 Jaguar-specific scanner. It reads all Jaguar modules and saves thousands in dealer diagnostic fees. Essential tool for S-TYPE ownership.
Jeep Grand Wagoneer · 2022–2024
Owner reports and NHTSA complaints describe repeated dead 12V batteries and no-start conditions on Grand Wagoneer, often after sitting overnight or a few days. The pattern is consistent with parasitic draw from modules not going to sleep (commonly telematics/infotainment-related controllers), leading to low voltage and cascading network faults.
Common Symptoms
- No-crank/no-start after sitting
- Multiple warning lights after jump start
- Remote start inoperative
- Battery voltage low message
- Repeated need for jump starts or battery replacement
How to Fix
Perform a parasitic draw test with an ammeter and use a scan tool to identify modules staying awake; update software per applicable Stellantis service bulletins and replace the failing module if it will not sleep. Replace the 12V battery if it has been deeply discharged multiple times and verify charging system output.
What you need to diagnose it
The fix here starts with a test, not a part — which repair you need depends on what the test finds.This issue involves U codes, which a basic engine-code reader cannot see.At least one code uses a manufacturer-specific format. No scanner recommendation is shown because family-level coverage cannot prove it can read that code.
UNI-T UT210E Low-Current DC Clamp Meter
1 mA resolution on the 2 A range — a 0.1 A meter reads a 50 mA drain as zero
$40–$70View
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Testing and isolating the fault is DIY work. Replacing or reprogramming a control module is not — most are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Duralast Platinum H7-AGM Group 94R main batteryOEMDuralast H7-AGM / SKU 319458
Confirm installed group, CCA, vent, terminal layout and VIN bec
- Duralast Platinum H8-AGM Group 49 main batteryOEMDuralast H8-AGM / SKU 319459
Do not substitute it for an installed H7 without confirming tray/
- Duralast Platinum AUX14 Group 400 AGM auxiliary batteryOEMDuralast AUX14 / SKU 755654
It is not the main battery; verify VIN/equipment and the installed auxiliary battery label
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Ford Transit · 2015–2022
GMC Sierra 3500HD · 2015–2023
Find U0100 by make
Browse every documented model and issue for your make.
U0100 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does U0100 mean?
U0100 stands for "Lost Communication with ECM/PCM." U0100 is a network communication code meaning a module has lost communication with the engine control module / powertrain control module (ECM/PCM) over the vehicle's data bus. The ECM/PCM is the brain that runs the engine, so when other modules can no longer 'talk' to it, the effects can be serious — a no-start, stalling, multiple warning lights, and many other modules logging faults at once. This is almost always a wiring, connector, power/ground, or bus fault, or a failure of the ECM/PCM itself, rather than a single sensor. It should be diagnosed promptly because the vehicle may be undrivable.
What are the most common causes of U0100?
The most common causes of U0100 are: Loss of power or ground to the ECM/PCM, CAN bus wiring damage, short, or open circuit, Corroded, loose, or damaged connectors at the module, Blown fuse feeding the ECM/PCM, Failed ECM/PCM, Another faulty module pulling down the data bus, Water intrusion or corrosion in a connector/harness. The specific cause varies by vehicle.
How much does it cost to fix U0100?
Repair costs for U0100 range from $80 to $3,500, depending on the vehicle and root cause.
Which vehicles are affected by U0100?
Au7o has documented U0100 across 25 vehicle models from 11 manufacturers: Audi, Cadillac, Chevrolet, Chrysler, Ford, GMC, Genesis, Jaguar, Jeep, Mercedes-Benz, Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.