Generic fault code
P0634 — Control module internal temperature A: too high
The control unit stores code P0634 when it detects this fault: “Control module internal temperature A: too high”.
Indicative severity: HighControl modules and outputs
Reviewed by Daniel Morales, founder of Reprorace SL, on
What does code P0634 mean?
The car's control units and the reference voltages they feed their sensors with. Sometimes the fault is in the control unit; often it is in its power supply or wiring.
- System
- P · Powertrain
- Area
- Control modules and outputs · Car system: CAN network and modules
- Type
- Generic (SAE J2012 / ISO 15031-6): the same meaning on every make
- Indicative severity
- High. Diagnose as soon as possible: it may affect safety or cause damage (engine, catalyst, brakes).
What usually causes code P0634?
- Thermal problem (cooling, thermostat, fan, overheating)
The most likely causes come first. Only a check on the car confirms which one is yours.
What are the symptoms of code P0634?
- Assorted warning lights or limp-home mode
- Starting problems or functions that do not respond
- Sometimes nothing you notice
These are the usual symptoms of this kind of fault: not all of them always appear, and sometimes you notice nothing.
Can I keep driving with code P0634?
Better not, except when you really have to. This fault may affect safety or damage the engine, the catalytic converter or the brakes. See a workshop as soon as possible; if you must move the car, drive gently and only short distances. If the light flashes, the car loses power, makes unusual noises or the brakes or steering feel different, stop somewhere safe and call for assistance.
This is guidance only: only someone who checks the car can say whether it is safe to drive.
An indicative description of the code's generic meaning. Each manufacturer may give it a different meaning, conditions or tests: always follow its service information and your workshop's advice.
What you can do yourself
For this kind of fault
Before suspecting the control unit, check the battery and its terminals: low voltage causes many of these codes. Replacing or reprogramming a control unit is a workshop job with the manufacturer's information.
Read the code and keep the report: with an ECO-LITE in the OBD socket you see it on your phone or computer, with the data captured when the fault happened.
Look for anything obvious: a loose connector, a disconnected hose, a fuel cap not closed properly or a low fluid level. Do not take apart anything you do not know.
Clear the code only after writing it down or after the repair. Clearing turns the light off, but it also deletes the freeze-frame data and the readiness monitors used at the inspection.
Drive normally for a few days and read the codes again. If the code comes back, the fault is still there: book the workshop and bring the report.
Read your car's fault codes on your phone
With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.
Related codes
- P062CInternal control module vehicle speed: performance
- P0630VIN: not programmed or incompatible - ECM/PCM
- P0631VIN: not programmed or incompatible - TCM
- P0632Odometer: not programmed - ECM/PCM
- P0633Immobilizer key: not programmed - ECM/PCM
- P0641Sensor reference voltage A, circuit open
P06xx codes: computer and output circuits
In the glossary
Read more: Remote OBD diagnostics: what it is, how it works and what it can't do