Meaning

The TCM has detected that the transmission ratio measured in sixth gear does not match the expected value. The module calculates the ratio by comparing input shaft speed to output shaft speed. The detected deviation exceeds the tolerance threshold defined by the manufacturer.

Common causes

• Worn or slipping clutch pack or band for sixth gear
• Stuck or failed shift solenoid for sixth gear
• Low ATF level or degraded/contaminated fluid
• Valve body fault causing insufficient hydraulic pressure
• Faulty input or output speed sensor producing an incorrect ratio calculation
• Mechanical internal damage to the automatic transmission

Symptoms

• MIL illuminated
• Transmission locked in limp-home mode
• Slipping or harsh engagement of sixth gear
• Vibration or shudder during gear engagement
• Reduced engine power output
• Abnormal or absent sixth gear engagement

Severity

What to do

1. Check ATF level and condition; replace if degraded or contaminated
2. Read all stored DTCs and monitor live input/output shaft speed data with a diagnostic scanner
3. Test resistance and operation of the sixth-gear shift solenoid
4. Inspect the valve body for corrosion, blockages, or valve wear
5. If hydraulic and electrical components test within spec, perform an internal transmission teardown to assess sixth-gear clutch pack wear

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