P0781 Fault Code in Toyota: Causes, Symptoms, and Fixes

The Transmission Control Module (TCM) has detected that the 1st-to-2nd gear shift did not occur as expected. This is more specific than P0780 (general shift fault) and points directly to a problem in the 1–2 shift process.

Symptoms:

1. Check Engine Light ON
2. Hard shift or no shift from 1st to 2nd
3. Transmission slipping during 1–2 shift
4. Vehicle stuck in limp mode
5. Harsh engagement when accelerating
6. Possible poor fuel economy

Common Causes:

1. Faulty shift solenoid (Shift Solenoid A or B, depending on design)
2. Low or dirty transmission fluid
3. Valve body issues – clogged passage, stuck valve
4. Worn 2nd gear clutch pack or band
5. Hydraulic pressure problems
6. Wiring/connector faults in shift solenoid circuit
7. Failed TCM/PCM (less common)

Diagnostic & Fix:

1. Check fluid – level and condition (burnt = overheating).
2. Inspect solenoids – test resistance, command ON/OFF with scanner.
3. Scan live data – see if TCM is commanding the 1–2 shift but transmission isn’t responding.
4. Check valve body – clean passages, look for sticking valves.
5. Inspect clutches/bands – worn friction elements may prevent proper 1–2 shift.
6. If all else checks out → internal rebuild may be required.