U0402: Invalid Data Received From Transmission Control Module
What to do
Expect reduced power and the transmission possibly holding one gear, and possibly a speedometer that reads oddly.
The most important thing: limp mode here does not mean your gearbox has failed. A transmission that is genuinely broken tells you first — slipping, banging into gear, noise, a burnt smell. If it felt completely normal until the warning light came on, that is a strong argument against anything mechanical.
Do not agree to a transmission overhaul or replacement on the strength of this code. The module is reporting a figure other systems cannot believe, and the usual cause is a sensor feeding it — a speed sensor or the range sensor that tells it which gear is selected — rather than the gearbox or the module.
Ask for the other stored codes to be read first, and for the transmission's sensors and wiring to be checked before anything is taken apart.
What this code means
The transmission control module is broadcasting data that cannot be accepted as true. See U0400 for the family's framing.
The transmission publishes a small number of values that other systems depend on absolutely: which gear is engaged, output shaft speed, fluid temperature, torque converter state, and whether a shift is in progress.
The gear position value is the one with consequences beyond the gearbox, and it is worth being specific about why. The engine module uses it to decide how much torque it may deliver — different gears permit very different levels — and the stability control system uses it as part of understanding what the vehicle is doing. An implausible gear report therefore makes the engine conservative and the stability systems cautious, which is felt as a car that has gone flat for no apparent reason.
Output shaft speed matters similarly. It is one of the vehicle's road speed sources, and where it disagrees with the wheel speeds the systems that compare them — stability control, cruise control, the speedometer itself — have to decide which to believe. A speedometer reading oddly alongside this code is that disagreement made visible.
As at U0401, the fault is usually upstream. The transmission module reports what its sensors tell it, so a failing output or input speed sensor, or a range sensor that cannot decide which gear is selected, makes it publish something impossible while the module itself is sound.
And the standing warning from U0101 applies with full force: limp mode here does not mean the gearbox has failed. A genuinely failed transmission announces itself mechanically — slipping, harshness, noise, burnt fluid. A transmission that felt perfect until the warning appeared, with a data code stored, is a sensor and wiring question rather than a mechanical one — and it should not lead to an overhaul quote.
Likely causes
Start here
- Faulty receiving module input · specialist
- Failed transmission speed sensor · moderate
- Damaged data bus wiring · moderate
- Corroded or loose connector · easy
Less common
- Software updated on one module only · specialist
- Faulty transmission control module · specialist
Symptoms
Components involved
Information, not instruction
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Community experience
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