U0101: Lost Communication With TCM
Key takeaways
- U0101 means another module on the car's data network stopped receiving messages from the transmission control module (TCM).
- Drive only short trips: the transmission may lock into one gear, and some trucks won't crank with this code.
- Test the battery, clean the terminals and check grounds and connectors before anyone replaces a module.
- GM, Nissan, Ford and Stellantis bulletins name U0101, pointing to wiring harness checks and software updates.
- Fixes range from about $20 for cleaning terminals to about $1,500 for a replaced and programmed TCM.
What U0101 means
Your engine computer (or another module) stopped hearing from the transmission computer. Modern cars have modules that talk to each other over a data network called the CAN bus. The transmission control module (TCM) sends regular messages; when another module misses them for longer than it allows, it stores U0101, “Lost Communication With TCM.” The code doesn’t say why the messages stopped. The TCM may have lost power or ground, a wire or connector may be faulty, or the module itself may have failed. On many cars the TCM sits on or inside the transmission, where heat and fluid make connectors a common weak point.
Is it safe to drive?
Short trips only. When the engine computer can’t reach the TCM, many transmissions drop into a fail-safe mode that holds one gear, which makes merging and highway speeds unsafe. The symptom that changes the answer: if the car is stuck in one gear, won’t shift out of park, or cranks and starts only some of the time, don’t count on it to get you anywhere far. Some trucks with this code won’t crank at all, so avoid parking it somewhere you can’t be towed from.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Weak battery or loose, corroded battery terminals | Battery load test; voltage during cranking; clean and tighten terminals | $20–$50 to clean; $150–$350 for a battery |
| Bad ground (engine or body ground strap, TCM ground) | Voltage drop test on the ground circuits | $100–$250 |
| Loose, corroded or fluid-soaked TCM connector | Inspect the connector at the TCM and at the transmission | $100–$250 |
| Blown fuse or relay feeding the TCM | Check power at the TCM connector | $20–$100 |
| Damaged network (CAN) wiring or a chafed harness | Resistance check across the network; scan for which modules are missing | $100–$250 |
| TCM software needing an update | A bulletin covers your make, model and year | $100–$200 |
| Failed TCM | Power, ground and network test good but the module won’t respond | $500–$1,500 replaced and programmed |
If you have several U codes at once (for example U0100 and U0101 together), suspect battery, grounds or the shared network wiring before any single module.
What to check first
- Test the battery and charging. Clean and tighten both terminals. If the code appeared after a jump start or a battery change, clear it and see if it returns. A battery that keeps dying sets communication codes too.
- Check the grounds. Engine-to-body and TCM grounds corrode quietly and cause intermittent faults.
- Check fuses and the TCM connector. Look for fluid in the connector, bent pins or a connector that isn’t latched.
- Scan every module. A shop checks which modules are talking and which aren’t; that points to one module or to the network.
- Look for a bulletin. The pattern is wiring and software: GM directs dealers to inspect the engine harness for shorting on 2019–2021 Silverado and Sierra 1500 trucks, Nissan covers a TCM communication error causing no-start on 2020–2021 Titans, and Ford and Stellantis have software or diagnostic procedures for F-150, Challenger, Charger and 300 models.
- Replace the TCM last, and only after power, ground and network all test good.
NHTSA data shows 70 complaints filed with NHTSA mention U0101, led by the Ford Focus with 6 and the Chevrolet Silverado 1500 with 5. Those are owner reports, not confirmed causes.
What it costs
The cheap outcome is clean terminals or a new battery, about $20–$350. The common outcome is a ground, connector or wiring repair at $100–$250. The expensive outcome is a replaced and programmed TCM, around $500–$1,500, more where the module is built into the transmission. Network testing before parts matters, because a new TCM won’t fix a bad ground.
Related codes
U0101 often shows up with U0100 (lost communication with the engine computer) or U0103 (lost communication with the gear shift module), and sometimes with P0562 (low system voltage), which points straight at the battery or charging system. P0700 may also appear, since the engine computer flags any transmission fault.
What owners report to NHTSA
70 complaints filed with NHTSA mention U0101, 66 of them since 2015, across 41 different models. The component owners most often filed it under: electrical system.
Most-reported models
| Vehicle | Complaints | Model years reported |
|---|---|---|
| FORD FOCUS | 6 | 2012, 2013, 2014, 2016 |
| CHEVROLET SILVERADO 1500 | 5 | 2019, 2020 |
| MAZDA MAZDA3 | 4 | 2006, 2010, 2012, 2013 |
| CHEVROLET COBALT | 3 | 2005, 2007 |
| GMC SIERRA 1500 | 3 | 2022, 2025 |
| CHEVROLET IMPALA | 3 | 2012, 2014 |
| JEEP WRANGLER | 3 | 2022 |
Manufacturer service bulletins that name U0101
124 technical service bulletins and manufacturer communications filed with NHTSA mention U0101, from 16 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- JEEP GRAND CHEROKEE (2023, 2024, 2025), bulletin 11010695: SHIFTER The service shifter message comes on in the cluster and the lever gets stuck in park "P" and it can be present the follwoing DTC: - U11E3 - TCM Lost communication with ESM on D-PT CAN - U0103 - Lost communication…
- ISUZU N-SERIES (2022), bulletin 10214883: Dealers, upfitters or bodybuilders may notice various warning lights on the dash illuminating and certain DTCs without an apparent cause during the initial installation and connection of telematics, GPS, and/or other aft…
- NISSAN TITAN (2020, 2021), bulletin 10186848: 2020-2021 TITAN/TITAN XD; TCM COMMUNICATION ERROR CAUSING A NO START CONDITION IF YOU CONFIRM The customer states the engine will not crank and will not start. (The incident may be intermittent.) And There is a U0101 DTC…
- CHEVROLET SILVERADO 1500 (2019, 2020, 2021), bulletin 10193465: This Preliminary information communicates the following issues and directs dealership to inspect the engine harness for shorting. Some customers may comment on any of the following concerns: - SES MIL - No Start - No Cra…
- GMC SIERRA 1500 (2019, 2020, 2021), bulletin 10193465: This Preliminary information communicates the following issues and directs dealership to inspect the engine harness for shorting. Some customers may comment on any of the following concerns: - SES MIL - No Start - No Cra…
- DODGE CHALLENGER (2021), bulletin 10222994: Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further inves…
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can a weak battery cause U0101?
Yes. Modules drop off the network when voltage sags, especially during cranking. A battery that tests weak, loose or corroded terminals, or a bad ground can set U0101 and several other U codes at once.
Do I need a new transmission if I have U0101?
Almost never. U0101 is a communication fault, not a mechanical one. The transmission itself is usually fine; the problem is power, ground, wiring or the control module.
Why is my car stuck in one gear with U0101?
When the engine computer can't talk to the TCM, or the TCM loses power, many transmissions go into a fail-safe mode that holds one gear so you can limp home. Fixing the communication fault restores normal shifting.
Can I clear U0101 and keep driving?
You can clear it, and if it came from a jump start or a battery change it may not come back. If it returns, the fault is real and needs testing before it strands you.