P0634Control Module Internal Temperature A Too High
- Generic OBD-II code · Powertrain
- Can trigger limp mode
- How the car detects it
- The module measures its own circuit board temperature with an internal sensor and sets P0634 when it overheats. In practice this concerns mainly transmission modules mounted in or on the gearbox, such as GM's 6T70/6T75 and 6L units with the module in the valve body, surrounded by transmission fluid. GM sets it at 142 °C or more for 5 s (Saab 9-4X: 146 °C), or at 50 °C or more with system voltage of 18 V or higher for 2 s, because overvoltage heats the output stages. The Saab 9-4X then goes into limp mode with only reverse and 5th gear, manual shifting disabled and maximum line pressure; GM's table rates it without the check engine light. Check transmission overtemperature (P0218) first, then fluid level and cooler, engine cooling and charging voltage. Faults of the internal temperature sensor circuit are P0666–P0669.
- What you may notice
- Transmission limp mode (fixed gear), harsh shifts
- Manual shifting disabled
- Transmission warning, check engine light depending on the maker
- Often together with transmission overtemperature (P0218)
- Likely causes
- LikelyTransmission fluid too hot: cooler clogged, lines kinked, air flow blocked, wrong level
- PossibleEngine overheating
- PossibleCharging system overvoltage (18 V or more)
- PossibleFaulty internal temperature sensor or valve body module
- RareHigh sustained load (towing, mountain driving, heat)
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.