P0780 Fault Code in Toyota: Causes, Symptoms, and Fixes

The Transmission Control Module (TCM) or Powertrain Control Module (PCM) has detected an improper gear shift or failure in the shifting process. Unlike more specific solenoid codes, this one is broad and can be triggered by multiple shift-related problems inside the transmission.

Possible Symptoms:

1. Check Engine Light (CEL) ON
2. Transmission slipping
3. Harsh or erratic shifting
4. Transmission stuck in one gear (limp mode)
5. Poor acceleration or loss of power
6. Reduced fuel economy

Common Causes:

1. Faulty shift solenoids (electrical or mechanical failure)
2. Hydraulic issues – low, dirty, or contaminated transmission fluid
3. Blocked or sticking valve body passages
4. Internal transmission damage – worn clutches, bands, or seals
5. Wiring or connector issues in the transmission circuit
6. Failed TCM/PCM (rare, but possible)

Diagnostic & Fix:

1. Check transmission fluid – level, color, smell (burnt fluid = overheating).
2. Scan live data – see if solenoids are being commanded but not responding.
3. Inspect wiring/connectors – corrosion or damage around transmission harness.
4. Test solenoids – electrical resistance and operation.
5. Check valve body – clean or repair if sticking.
6. If above are fine → inspect clutches and bands (internal repair or rebuild may be needed).