What it means
The transmission control module detects a performance fault in its gear-ratio control function.
At a glance
- Usually lights the check-engine light
How it works
The transmission control module (TCM) coordinates gear changes using transmission speed data, solenoids and hydraulic controls. It compares the resulting gear ratio with the ratio expected for the commanded gear; this code sets when the TCM’s gear-ratio control function does not perform as expected.
Common causes
Most likely first.
- Incorrect or missing transmission speed data
- Shift solenoid or valve-body fault
- TCM or related wiring fault
Symptoms
- Transmission warning light
- Harsh, delayed, or erratic shifts
- Slipping or limited shifting
How to diagnose it
- Record freeze-frame data and scan for related transmission codes to see which gear, speed signals or control conditions were present when the ratio fault occurred.
- Check the transmission fluid level and condition using the vehicle’s specified procedure, since low or degraded fluid can interfere with hydraulic gear control.
- Inspect the TCM connectors, transmission harness and grounds for loose connections, corrosion, damage or fluid intrusion that could affect speed data or solenoid control.
- Compare input and output speed readings with commanded gear and vehicle speed during a controlled road test, looking for missing or implausible data that could distort the calculated ratio.
- If the speed data is credible, test the relevant shift solenoid and valve-body operation against the manufacturer’s specification, then check TCM power, ground and wiring before suspecting an internal module fault.
Common fixes
- Correct the transmission fluid level or condition if it is outside the specified range.
- Repair damaged wiring, poor grounds or loose or corroded TCM and transmission connectors.
- Replace a faulty speed sensor or repair its circuit if the data check identifies an input problem.
- Repair or replace a sticking shift solenoid or valve-body component after confirming the hydraulic fault.
- Repair or replace the TCM only after its power, ground, wiring and related components pass checks.
Can I keep driving?
Avoid hard acceleration, towing and long trips if shifts are harsh, delayed or slipping; continued operation can worsen transmission damage. If the transmission loses drive or becomes unpredictable, stop in a safe place and arrange assistance.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.