P0738
TCM Engine Speed Output Circuit Low
- Severity
- Medium
- Driving
- Drivable — book it in
The engine speed output circuit from the transmission module is stuck low - typically shorted to earth or open circuit. The module cannot deliver the engine speed signal to whatever consumes it, so that system loses its reading while the transmission itself carries on normally.
Possible causes
- CommonWiring shorted to earth or open circuit between the transmission module and the receiving module
- CommonCorroded connector at either end
- PossibleChafed harness shorting against the body or engine
- PossibleFailed receiving module loading the circuit
- RareFailed transmission control module output driver
What you might notice
- Rev counter dead or reading wrong
- Check engine light on
- Usually no effect on how the car drives
What to check, in order
- Disconnect the receiving module and see whether the low reading persists. If it clears, the receiving module is loading the circuit.
- Inspect both connectors for corrosion.
- Follow the wire looking for chafe damage.
- Check for aftermarket splices into this circuit.
- Confirm the transmission module has good power and earth before condemning it.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Transmission
P0700P0701P0702P0703P0704P0705P0706P0707P0708P0709P0710P0711P0712P0713P0714P0715P0716P0717P0718P0719P0720P0721P0722P0723P0724P0725P0726P0727P0728P0729P0730P0731P0732P0733P0734P0735P0736P0737P0738P0739P0740P0741P0742P0743P0744P0745P0746P0747P0748P0749P0750P0751P0752P0753P0754P0755P0756P0757P0758P0759P0760P0761P0762P0763P0764P0765P0766P0767P0768P0769P0770P0771P0772P0773P0774P0775P0776P0777P0778P0779P0780P0781P0782P0783P0784P0785P0786P0787P0788P0789P0790P0791P0792P0793P0794P0795P0796P0797P0798P0799