Gear 1 Incorrect Ratio
When gear 1 is engaged, the measured ratio between the input- and output-shaft speed sensors does not match the expected ratio for that gear. This means the transmission is slipping in gear 1 rather than transmitting power solidly. Causes: worn clutch packs or bands, low fluid level or pressure, a stuck shift solenoid, or a valve-body fault affecting gear 1.
Affected components
- Transmission clutch pack
- Transmission valve body
- Transmission fluid
Common causes
- High likelihood: 1st gear clutch pack worn
- Medium likelihood: Line pressure low (pump or valve body)
Possible symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Diagnostic notes
- The malfunction indicator lamp may illuminate
- Reduced-power or limp mode may occur
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.