U0101 Lost communication with the transmission computer

Lost communication with TCM

U0101 in short

U0101 means another module stopped hearing from the transmission computer. Wiring, connectors and power or ground to that computer are the usual causes, and some makers fix it with a software update or a repair inside the transmission. Get it checked soon; stop if the transmission stops shifting or loses drive.

The transmission computer shares data with the engine computer, the gear selector and the cluster over the car's network. When a module stops receiving its messages, it stores U0101.

The transmission computer is often mounted on or inside the transmission, so its wiring sees heat, vibration and fluid. GM fixed U0101 with a backed-out terminal in the transmission harness connector, and on a 2010 Camaro with water inside the transmission.

Some makers have their own fixes: Nissan has a service bulletin for a Titan and Frontier that will not crank with U0101 stored, and FCA replaces the valve body on 2023-2025 Grand Cherokee and Wagoneer models with U0101 or U0402.

Most likely causes

  1. Transmission harness connector or network wiring fault

    Common general cause
    Why it ranks here
    Network faults are usually harness faults. GM's 08-07-30-021 family repaired a backed-out terminal in the transmission harness connector for U0101 and related codes on 2007-2014 trucks.
    What would change this
    Rises if the fault is intermittent with bumps or heat, or the connector shows a pushed-back pin or fluid. Falls if bus resistance and the connector are good.
    How to test the transmission control module (tcm)

  2. Transmission computer power or ground fault, or low battery voltage

    Common general cause
    Why it ranks here
    A module without stable power drops off the network. Nissan's bulletin treats a no-crank with U0101 on the Titan and Frontier as a transmission computer communication error.
    What would change this
    Rises if the transmission computer does not answer a scan tool and its fuses, power or grounds test low. Falls if supply is good.
    How to test the transmission control module (tcm)

  3. Transmission computer software, or an internal transmission or valve body fault (some models)

    Supported by vehicle data
    Why it ranks here
    FCA's 21-016-25 replaces the valve body for U0101/U0402 on 2023-2025 Grand Cherokee and Wagoneer, Ford's 16-0044 covers the DPS6, and GM PIP-4678B found water inside the transmission on a 2010 Camaro.
    What would change this
    Rises if a dealer finds a bulletin for your VIN or the fluid is milky or contaminated. Falls if no bulletin applies and the fluid is clean.
    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 and note which ones stored U0101 and whether the transmission computer answers the scan tool.

    Low riskTool: scan tool that reads all modules

    • IfThe transmission computer does not respond

      It meansCheck its power, ground and connector next.

      Go to step 2

    • IfIt responds but U0101 keeps returning, often with other U-codes

      It meansSuspect intermittent wiring or a connector.

      Go to step 3

  2. Test the 12-volt battery and check the battery terminals and grounds.

    Low riskTool: battery tester

  3. Ask a dealer whether your VIN has a bulletin for U0101. Nissan (Titan, Frontier), Ford (DPS6), GM and FCA have issued them.

    Low risk

  4. Have the transmission harness connector inspected for pushed-back pins, corrosion or fluid, and the network wiring measured.

    Best left to a shopTool: multimeter, wiring diagram

    Warning:The connector is under the car near hot exhaust and moving parts. Only work under a car on proper stands with the engine off; a shop is the safer choice.

Symptoms

  • Check engine light with a transmission or wrench warning
  • Transmission stuck in one gear or shifting harshly
  • Engine will not crank, sometimes only intermittently
  • "Transmission Hot" or similar message without real overheating
  • Transmission loses drive while moving Gets more serious: stop and have it checked.

How to fix

  1. Have the 12-volt battery tested and make sure the terminals are clean and tight.

  2. Ask a dealer whether your VIN has an open bulletin or software update for U0101.

Parts and cost context

  • Transmission control module (TCM):A replacement transmission computer usually needs programming. Rule out the connector, wiring and bulletins first. 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

Nissan

  • 2020–2021 · Titan

    Supported by vehicle data

    Nissan NTB21-001B: a no-crank or no-start with U0101 is treated as a transmission computer communication error (2020 Frontier has NTB21-002A). Whether the bulletin is still current is not verified.

  • 2020 · Frontier

    Supported by vehicle data

    Nissan NTB21-002A covers the same no-crank with U0101 as the Titan bulletin. Whether the bulletin is still current is not verified.

  • NTB21-001BStatus unverified

    TCM communication error causing a no start

    2020–2021titan · issued · NHTSA 10222864

    Service information for a Titan that will not crank or start (may be intermittent) with U0101 stored in the engine or shift control unit.

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

  • NTB21-002AStatus unverified

    TCM communication error causing a no start

    2020frontier · issued · NHTSA 10222865

    Service information for a Frontier that will not crank or start (may be intermittent) with U0101 stored.

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

Jeep

  • 2023–2025 · Grand Cherokee

    Supported by vehicle data

    FCA 21-016-25 replaces the valve body for U0101 or U0402 (also Grand Cherokee L, Wagoneer, Grand Wagoneer). Whether the bulletin is still current is not verified.

  • 21-016-25 REV. CStatus unverified

    Valve body replacement for U0101 or U0402

    2023–2025grand-cherokee, grand-cherokee-l, wagoneer, grand-wagoneer · issued · NHTSA 11022007

    Replace the transmission valve body when the MIL is on with U0101 or U0402.

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

Chevrolet

  • 2010 · Camaro

    Supported by vehicle data

    GM PIP-4678B links U0101 with water inside the transmission, no forward gears and harsh shifts. Check the fluid. Whether the bulletin is still current is not verified.

  • 2011–2013 · Silverado 1500

    Supported by vehicle data

    GM PI-0531-B: a "Transmission Hot - Idle Engine" message may come with U0101. Whether the bulletin is still current is not verified.

  • PI-0531-BStatus unverified

    Transmission Hot - Idle Engine message, U0101 may be set

    2011–2013silverado-1500 · issued · NHTSA 10053223

    Preliminary information for a Silverado showing "Transmission Hot - Idle Engine" with U0101 possibly set.

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

  • PIP-4678BStatus unverified

    Water in transmission with U0073, U0100, U0101

    2010camaro · issued · NHTSA 10034433

    Check transmission fluid condition for water contamination when these codes appear with shifting problems.

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

  • U0100Lost communication with the engine or powertrain computer

    Shares causes Supported by vehicle data

    GM's GMLAN bulletin and Ford's DPS6 bulletin list U0100 and U0101 together. Check shared wiring and power first.

  • U0402A module received invalid data from the transmission computer

    Shares causes Supported by vehicle data

    FCA's 21-016-25 covers U0101 (lost contact with the transmission computer) and U0402 (bad data from it) with the same valve body repair on 2023-2025 Grand Cherokee and Wagoneer.

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

    Shares causes Supported by vehicle data

    GM lists U0073 with U0101 for the same harness fault and for water in a 2010 Camaro transmission.

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

    Shares causes Supported by vehicle data

    Ford's 16-0044 lists U0101 with U0100, U1013, U3003 and P0606 on Fiesta and Focus models with the DPS6 transmission, with no start, loss of engagement or loss of power.

All Module network (CAN bus) communication codes

U0101 questions

Can I keep driving with U0101?

Only gently and only if the transmission shifts normally. If it stops shifting, slips out of drive or shows a transmission warning, stop and have it checked.

Do I need a new transmission computer?

Not as a first step. Connector and wiring faults, low battery voltage and software are common. Some makers fix U0101 with a bulletin repair.

Sources and review

  1. Nissan NTB21-001B: TCM communication error causing a no start — Nissan North America / NHTSA ,
  2. Ford TSB 16-0044: DPS6 no start, no engagement or loss of power with U0100, U0101, U1013, U3003, P0606 — Ford Motor Company / NHTSA ,
  3. GM 08-07-30-021: Loss of high-speed GMLAN, intermittent no crank, DTCs U0073/U0100/U0101/U0102/U0121/U0140 — General Motors / NHTSA ,
  4. 2023 Integra Owner's Manual: Indicators — American Honda Motor Co.
  5. ASE L1 study guide: Network U-codes — Open Exam Prep
  6. Nissan NTB21-002A: TCM communication error causing a no start — Nissan North America / NHTSA ,
  7. FCA 21-016-25 REV. C: Valve body replacement for U0101 / U0402 — FCA US LLC / NHTSA ,
  8. GM PIP-4678B: Water in transmission, no forward gears, DTCs U0073, U0100, U0101 — General Motors / NHTSA ,
  9. GM 08-07-30-021H: Loss of high-speed GMLAN communications, intermittent no crank — General Motors / NHTSA ,
  10. GM PI-0531-B: Transmission Hot - Idle Engine message, U0101 may be set — General Motors / NHTSA ,
Last reviewed
Written by
Saurabh K.
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