Transmission Control Unit (TCU) Data Validity - Incorrect Gear Ratio
This code indicates the Transmission Control Unit has detected an invalid gear ratio in the transmission.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The computer expects the transmission to shift into a certain gear, but the actual ratio doesn't match what it should be, which can mean slipping or mechanical issues inside the transmission.
What the computer is actually seeing
The TCU is constantly monitoring the input speed and output speed of the transmission. When the calculated gear ratio, using these speeds, does not match the expected range, the TCU sets this fault code. For example, if input speed is 1500 RPM and the output speed is 1000 RPM, the expected ratio should be 1.5:1.
What a healthy reading looks like
Expected input and output speed ratios typically range from 0.1 to 4.0 depending on the gear, with a specific ratio for each gear in the transmission. Values will vary by vehicle and transmission type.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the transmission fluid level and condition; flush if dirty or low.
- 2Inspect wiring and connectors to the transmission speed sensors for damage or corrosion.
- 3Test the input and output speed sensors with a multimeter; expect output near 0-5 volts at idle under normal conditions.
- 4Verify that the TCM is receiving correct input from the speed sensors during a test drive; log data using a scanner.
Common causes
- Worn transmission components
- Faulty speed sensors (input/output)
- Corrosion or damage to wiring harness
- Malfunctioning Transmission Control Module (TCM)
- Low transmission fluid level or dirty fluid
Typical repair cost
$$$
Related codes
Frequently asked questions
Can I drive the vehicle with this code?
Yes, but excessive slippage may occur, leading to further damage; address it soon.
Will this code come back after a reset?
If the issue isn’t resolved, it will likely return after a few drive cycles.
What if this code appears with other transmission-related codes?
Address all codes; they often point to a common underlying issue.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →