Network, generic

U0101 Lost Communication With TCM

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

TCM without power or ground (fuse, relay, connector)
Spread or corroded terminals at the transmission harness connector
Chafed or open CAN lines to the TCM
TCM internally faulty, overheated or not programmed

Symptoms

  • MIL on, transmission warning in the cluster
  • Gear indicator blank or flashing
  • Transmission locked in one gear
  • Scan tool cannot reach the TCM

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–1,200
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Check TCM power and ground
  2. Check network wiring

Parts involved

tcmcan bus wiring

Related codes

U0073U0100U0302U0402

References: gsi.ext.gm.com, fordservicecontent.com, newtonnet.co.uk, saabwisonline.com.