P0738TCM Engine Speed Output Circuit Low
- Generic OBD-II code · Powertrain
- How the car detects it
- Some transmission modules pass an engine speed signal on to other devices such as a tachometer over a wire of their own. CARB requires output circuits to be checked. No manufacturer document available to us uses P0737–P0739 – engine speed is shared over CAN today; the description follows CARB and the engine module's own speed output (P0654), which sends, for example, two pulses per revolution. P0738 means this output is too low, typically shorted to ground, so it can no longer switch high. The opposite is P0739, the general fault P0737. A tachometer or dependent display then reads zero or jumps, while driving is usually unaffected.
- What you may notice
- Tachometer at zero or jumping
- Warning lamp depending on manufacturer
- Usually no effect on driving
- Likely causes
- LikelyOutput wire shorted to ground
- PossibleReceiver shorted internally
- PossibleConnector corroded
- RareDriver stage in the transmission module faulty
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.