Meaning

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

Common causes

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

Symptoms

• MIL illuminated
• Transmission locked in limp-home mode
• Slipping or harsh engagement of third gear
• Shudder or vibration during third gear engagement
• Abnormal engine RPM rise without corresponding vehicle acceleration
• Reduced engine power output

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 third-gear shift solenoid
4. Inspect the valve body for blockages, corrosion, or hydraulic piston wear
5. If hydraulic and electrical components test within specification, perform an internal transmission teardown to assess third-gear clutch pack wear

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