U0100 Lost communication with the engine or powertrain computer

Lost communication with ECM/PCM "A"

U0100 in short

U0100 means another module on the car's network stopped hearing from the engine computer. The usual cause is wiring: a loose connector, a backed-out terminal, or a power or ground problem at the engine computer, often from a weak battery. Get it checked soon, and stop if the car loses power or stalls.

Modern cars connect their computers on a shared data network, usually CAN. Each module expects regular messages from the engine computer. When those messages stop arriving for long enough, the listening module stores U0100.

The code is stored by the module that lost contact, not by the engine computer, so the instrument cluster, transmission computer, ABS or other modules may all store it at once. The ASE study material stresses that which module stored the code matters as much as the code itself, and that network faults are usually wiring rather than a failed module.

Makers have found several causes: GM fixed a backed-out terminal in the transmission harness connector on its 2007-2014 trucks, GM had dealers test the engine computer wake-up circuit on 2020-2022 Silverados, and Ford, Volkswagen and FCA have bulletins for no-start conditions or software and module replacement.

Most likely causes

  1. Damaged wiring, loose connector or backed-out terminal on the data network or at the engine computer

    Common general cause
    Why it ranks here
    ASE study material says network failures are usually harness faults, not modules. GM's 08-07-30-021 bulletin family fixed U0100 on 2007-2014 trucks by repairing a backed-out terminal in the transmission harness connector.
    What would change this
    Rises if the code is intermittent, comes with gauge flicker or door lock cycling, or CAN resistance reads 120 ohms or more. Falls if bus resistance is about 60 ohms and wiggling harnesses changes nothing.

  2. Engine computer power, ground or wake-up circuit fault, or a weak 12-volt battery

    Common general cause
    Why it ranks here
    A module that loses power or ground goes silent on the network. GM's PIT6198 has dealers test the accessory wake-up circuit to the engine computer for power on 2020-2022 Silverados with U0100 at start-up.
    What would change this
    Rises if the battery tests weak, voltage drops sharply when cranking, or the engine computer will not talk to a scan tool at all. Falls if supply and ground circuits test good.

  3. Engine computer software fault or a failed engine computer

    Supported by vehicle data
    Why it ranks here
    Ford (2020 Escape) and FCA (2021-2022 Renegade) bulletins update or replace the powertrain computer for U0100, and Volkswagen has a bulletin for no ECM communication. These are make-specific, so it ranks below wiring and power.
    What would change this
    Rises if a dealer finds a bulletin for your VIN or the computer still will not communicate with good power, ground and bus wiring. Falls if it communicates normally.
    How to test the engine control module (ecm / pcm)

  4. Transmission control fault on Ford DPS6 (Fiesta, Focus)

    Supported by vehicle data
    Why it ranks here
    Ford's 16-0044 lists U0100 with U0101, U1013, U3003 and P0606 on 2011-2016 Fiesta and 2012-2016 Focus with the DPS6 transmission, with no start, loss of engagement or loss of power.
    What would change this
    Rises on a DPS6 Fiesta or Focus with the transmission codes listed in the bulletin. Not relevant on other vehicles.
    How to test the transmission control module (tcm)

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Scan every module, not just the engine computer, and note which modules stored U0100 and what other U-codes are present.

    Low riskTool: scan tool that reads all modules

    • IfSeveral modules store U0100 and other lost-communication codes together

      It meansA shared wiring or power problem is more likely than a single bad module.

      Go to step 2

    • IfThe engine computer itself does not respond to the scan tool

      It meansCheck its power, ground and wake-up circuit.

      Go to step 2

    • IfOnly one module stores U0100

      It meansLook at the wiring between that module and the network first, then check for bulletins.

      Go to step 3

  2. Test the 12-volt battery and check that the battery terminals and main grounds are clean and tight.

    Low riskTool: battery tester or multimeter

  3. Ask a dealer whether your VIN has a bulletin or software update for U0100. GM, Ford, FCA and Volkswagen have issued them.

    Low risk

  4. With the key off, measure resistance between CAN-high and CAN-low at the diagnostic connector, then check the engine computer's power, ground and network pins.

    Use cautionTool: multimeter

    Warning:Disconnect nothing with the ignition on, and do not probe airbag (yellow) connectors. If you are not comfortable back-probing connectors, let a shop do it.

Symptoms

  • Check engine light and several warning lights at once
  • Gauges flicker or drop to zero
  • Intermittent crank/no-start or no-start
  • Transmission will not shift or engage, or the car loses power while driving Gets more serious: stop and have it checked.
  • Engine stalls Gets more serious: stop and have it checked.

How to fix

  1. Check that the battery terminals are clean and tight and have the battery tested.

  2. Ask a dealer whether your VIN has an open bulletin or software update for U0100.

  3. Write down every code from every module before anything is cleared, so the pattern is not lost.

Parts and cost context

  • engine computer:Do not replace the engine computer until power, ground and network wiring are proven good. A new computer usually needs programming to the car. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2007–2014 · Silverado 1500

    Supported by vehicle data

    GM's 08-07-30-021 bulletins tie U0100 with other lost-communication codes, no crank and shifting problems to a backed-out terminal in the transmission harness connector on these trucks (also Tahoe, Suburban, Sierra, Yukon, Escalade). Whether the bulletin is still current is not verified.

  • 2020–2022 · Silverado 1500

    Supported by vehicle data

    GM PIT6198: for a check engine light at startup with U0100, test the engine computer's accessory wake-up circuit for power. Whether the bulletin is still current is not verified.

  • 08-07-30-021HStatus unverified

    Loss of high-speed GMLAN communications, intermittent no crank

    2007–2014silverado-1500, tahoe, suburban, avalanche, corvette · issued · NHTSA 10113715

    Repair for loss of high-speed GMLAN data, intermittent no crank, gauge fluctuation, door lock cycling and transmission that may not shift. The earlier issue of this bulletin repairs a backed-out terminal in the transmission harness connector. Also covers GMC, Cadillac and Hummer trucks.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIT6198Status unverified

    SES light at startup with U0100

    2020–2022silverado-1500, silverado-2500-hd, silverado-3500-hd · issued · NHTSA 11007183

    Test the accessory wake-up circuit to the engine computer for power.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Ford

  • 2012–2016 · Focus

    Supported by vehicle data

    On DPS6 automatics, Ford 16-0044 lists U0100 with U0101, U1013, U3003 and P0606 and loss of engagement, no start or loss of power. Also 2011-2016 Fiesta. Whether the bulletin is still current is not verified.

  • 2023–2025 · F-150

    Supported by vehicle data

    Ford SSM 54216 covers crank/no start with multiple warning lights and U0100 in several modules. Whether the message is still current is not verified.

  • 16-0044Status unverified

    DPS6 no start, no engagement or loss of power with U0100, U0101, U1013, U3003, P0606

    2011–2016fiesta, focus · issued · NHTSA 10075274

    Service information for 2011-2016 Fiesta and 2012-2016 Focus with the DPS6 transmission that lose engagement, will not start or lose power with these codes.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • SSM 54216Status unverified

    Crank/no start with multiple warning indicators and U0100

    2023–2025f-150 · issued · NHTSA 11023204

    Service message for F-150s that crank but do not start with U0100 stored in several modules.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • SSM 49157Status unverified

    MIL with U0100, U0401 and other codes

    2020escape · issued · NHTSA 10180361

    Service message for 2020 Escape with the MIL and possibly the wrench light on; the summary points to software.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Jeep

  • 2021–2022 · Renegade

    Supported by vehicle data

    FCA bulletin 1809723 replaces the powertrain control module for U0100 and related codes. Whether the bulletin is still current is not verified.

  • 1809723Status unverified

    PCM replacement for U0100 and related codes

    2021–2022renegade · issued · NHTSA 10243282

    Replaces the powertrain control module when the MIL is on with U0100 (lost communication with the engine computer) or related codes.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • U0101Lost communication with the transmission computer

    Shares causes Supported by vehicle data

    GM's GMLAN bulletin lists U0100 and U0101 together from one backed-out terminal, and Ford's DPS6 bulletin lists both. When both appear, check shared wiring and power before either module.

  • U0073A module found its data network (bus A) switched off or not working

    Shares causes Supported by vehicle data

    U0073 means a module saw the bus itself go down. GM's bulletin lists it with U0100 from the same harness fault. Fix the bus fault first.

  • U0401A module received invalid data from the engine or powertrain computer

    Shares causes Supported by vehicle data

    Ford's 2020 Escape bulletin lists U0100 and U0401 together, which points to the engine computer or its software rather than two separate faults.

  • P0606A control module found a fault in its own processor or programming

    Shares causes Supported by vehicle data

    Ford's 16-0044 lists U0100 with U0101, U1013, U3003 and P0606 on 2011–2016 Fiesta and 2012–2016 Focus with the DPS6 transmission.

All Module network (CAN bus) communication codes

U0100 questions

Does U0100 mean my engine computer is bad?

Not usually. The code means other modules lost contact with it. Wiring, connectors, power and ground, or a weak battery are more common causes. Prove those good before replacing the computer.

Is it safe to drive with U0100?

If the car starts and drives normally, drive gently to a shop soon. Stop if it loses power, stalls or the transmission stops engaging.

Sources and review

  1. Ford TSB 16-0044: DPS6 no start, no engagement or loss of power with U0100, U0101, U1013, U3003, P0606 — Ford Motor Company / NHTSA ,
  2. GM 08-07-30-021H: Loss of high-speed GMLAN communications, intermittent no crank — General Motors / NHTSA ,
  3. 2023 Integra Owner's Manual: Indicator, Coming On/Blinking — American Honda Motor Co.
  4. ASE L1 study guide: Network U-codes — Open Exam Prep
  5. GM 08-07-30-021: Loss of high-speed GMLAN, intermittent no crank, DTCs U0073/U0100/U0101/U0102/U0121/U0140 — General Motors / NHTSA ,
  6. GM PIT6198: SES MIL at startup with DTC U0100 — General Motors / NHTSA ,
  7. Ford SSM 49157: 2020 Escape MIL with U0100, U0401, P166B, P1753, P0929, P0919 — Ford Motor Company / NHTSA ,
  8. FCA 1809723: PCM replacement, U0100 lost communication with ECM — FCA US LLC / NHTSA ,
  9. VW TT 01 19 05_6: Engine crank, no start or no ECM communication with U0100 — Volkswagen of America / NHTSA ,
  10. Ford SSM 54216: 2023-2025 F-150 crank/no start with multiple warning indicators and U0100 — Ford Motor Company / NHTSA ,
Last reviewed
Written by
Saurabh K.
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