P0728
Engine Speed Input Circuit Intermittent
- Severity
- High
- Driving
- Drive only to a garage
The signal from the engine speed input circuit is dropping out intermittently - present, then briefly absent, then back. The module usually reacts by dropping into limp mode for the rest of the journey and recovering after a restart, which is why this fault often presents as a transmission that misbehaves once and then seems fine.
Possible causes
- CommonLoose, corroded or backed-out connector pin
- CommonChafed or fatigued wiring making contact until it moves
- CommonMetal debris intermittently bridging the sensor tip
- PossibleFailing sensor that drops out when hot
- PossibleDamaged reluctor ring with one bad tooth
- PossibleInternal harness beginning to fail
What you might notice
- Transmission drops into limp mode occasionally and recovers after a restart
- Momentary harsh shift or flare
- Speedometer needle dropping briefly
- Fault linked to bumps, heat or wet weather
What to check, in order
- Note the conditions. Over bumps means wiring, when hot means the sensor, in the wet means the connector - this single observation is the most useful diagnostic step available for an intermittent fault.
- Wiggle-test the harness and connector with the live data screen showing the speed reading.
- Inspect the connector for a backed-out pin and for corrosion.
- Inspect the sensor tip for debris.
- Check the fluid level and condition.
- Resist replacing the sensor on the strength of an intermittent code alone - confirm the dropout at the sensor first.
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