What U0402 means
Another computer in the car is receiving data from the transmission control module that doesn't make sense, such as a frozen or out-of-range value. Unlike a lost-communication code, the transmission module is still talking. Outdated transmission software, a fault inside that module or network interference is usually behind it, and the transmission often goes into limp mode.
How the engine computer detects it
A control module is communicating with the transmission control module but receives implausible data — wrong checksum, frozen value, or out-of-range value. Often results in transmission limp-home.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- TCM software bug or outdated calibration Possible
- TCM internal sensor or processing fault Possible
- CAN corruption causing checksum errors Possible
How to diagnose U0402
- Check battery voltage and the battery terminals. Low voltage can make modules send bad data.
- Read codes from all modules with a scanner that supports the transmission. Note which module stored U0402 and any transmission codes, which often reveal the real problem.
- Check for software updates and service bulletins for the transmission module. Reprogramming is a common fix and needs a dealer or a shop with programming tools.
- With the ignition off, inspect the transmission module connectors and grounds for corrosion or water. Where the module sits depends on the car; on some it's inside the transmission.
- A shop checks the network wiring between the modules for damage or interference.
- If the module itself is faulty, it must be replaced and programmed to the car.
Vehicles that report U0402 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Jeep Cherokee | 2014–2017 | 11 | 53k | |
| Ram 1500 | 2016–2025 | 5 | — | |
| Jeep Renegade | 2015–2018 | 3 | — |
Counts of owner complaints to the NHTSA that mention U0402 (33 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.
Reading the code
- U
- Network
- 0
- Generic (SAE) code
- 402
- Specific fault
Questions drivers ask
Can I drive with code U0402?
If it shifts normally, drive carefully to a shop. If it's stuck in one gear, shifts harshly or won't move out of Park, don't drive it, especially on the highway: have it towed.
Often reported together
Codes that owners mention in the same NHTSA complaints as U0402. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.