P0728Engine Speed Input Circuit Intermittent
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- The transmission module needs engine speed for converter slip, shift quality and to check the turbine speed. Today it almost always arrives over CAN from the engine module with a validity flag; only GM's 2007 Allison 1000 tables show a separate engine speed sensor read by the transmission module. P0728 means the engine speed signal at the transmission module drops out briefly. No manufacturer document available to us uses this code: GM's Allison 1000 detects jumps and noise of this input under P0726/P0727, and Saab's bus-based systems use those codes, too. By analogy with P0718/P0723 dropouts are counted. A loose contact in the signal or CAN circuit or an intermittent crankshaft sensor fault in the engine module is the likely cause; shifts may be harsh at times.
- What you may notice
- Occasional transmission warning lamp
- Harsh shift now and then
- Converter clutch releases occasionally
- Likely causes
- LikelyLoose contact in signal or CAN circuit
- PossibleSensor (if fitted) dirty or loose
- PossibleIntermittent crankshaft sensor fault in the engine module
- RareTransmission module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- 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.