Meaning

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

Common causes

• Worn or slipping clutch pack or band for second gear
• Stuck or failed shift solenoid for second gear
• Low ATF level or degraded/contaminated fluid
• Valve body fault causing insufficient hydraulic pressure in the second 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 second gear
• Shudder or vibration during the 1–2 upshift
• Abnormal engine RPM rise in second gear
• 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 second-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 second-gear clutch pack wear

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