U0101Lost Communication With TCM
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- U0101 means the transmission controller has dropped off the bus as seen by another node, mostly the engine controller. GM's 2019 truck ECMs watch eight TCM frames, most of them at 500 ms intervals, and set the code as Type A after battery and run voltage have exceeded 11 V for 3 s, provided U0073 is not active; GM's electronic range selector logs it as Type B after 1 s, the hybrid processor in the same table after 5 s. Ford's 2023 diesel summary flags the code when the TCM's master frame has been absent beyond 1 s, while the 2012 summary checks it only where the TCM is a separate unit. U0402 covers implausible TCM data, U0302 a software mismatch. Typical effects: dead gear display, fixed gear, MIL.
- What you may notice
- MIL on, transmission warning in the cluster
- Gear indicator blank or flashing
- Transmission locked in one gear
- Scan tool cannot reach the TCM
- Likely causes
- LikelyTCM without power or ground (fuse, relay, connector)
- PossibleSpread or corroded terminals at the transmission harness connector
- PossibleChafed or open CAN lines to the TCM
- RareTCM internally faulty, overheated or not programmed
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.