TCM Power Input Signal Low

Possible causes

• CommonA weak battery, a poor connection, or high resistance in the supply
• CommonCorroded or loose battery terminals
• CommonCorroded earth point
• CommonFailing alternator
• PossibleDamaged supply wiring
• PossibleFailing supply relay

What you might notice

• Harsh shifting or limp mode
• Battery or charging warning light
• Lights dimming or unusually bright
• Slow cranking
• Check engine light on

What to check, in order

1. Measure battery and charging voltage before touching anything else.
2. An overcharging alternator boils the battery and damages electronics across the whole vehicle. If voltage is high, treat it as urgent rather than as a transmission problem.
3. Perform a voltage drop test on the supply and earth circuits.
4. Clean and tighten the battery terminals and earth straps.
5. Check the supply fuses and relay.
6. Fix the electrical supply before diagnosing anything else the transmission is doing. Almost every other symptom will follow it.