Powertrain, generic · Computer and auxiliary outputs

P0654 Engine RPM Output Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The engine module switches this hard-wired output with its own driver and checks the circuit electrically (open, short to ground or voltage) – it cannot see whether the lamp lights; on CAN-based cars such faults appear as U codes. P0654 concerns the engine speed output: the module turns the crankshaft signal into a cleaned-up square wave for the tachometer and other modules – Saab's 1999 9-3, for example, sends two pulses per revolution, about 30 Hz at idle. P0654 reports an open circuit or other fault on this output. Saab's EDC16 diesels use P0654 differently (a sensor supply group). No manufacturer document available to us uses this code; the description follows CARB and the component. The tachometer then reads zero or jumps; devices using the signal may fail, while the engine itself runs normally because the crankshaft input is intact.

Likely causes

Wire between module and tachometer or receiver open, connector corroded
Output wire shorted
Instrument cluster or receiving module faulty (input stage)
Output driver in the module faulty

Symptoms

  • Tachometer reads zero or jumps
  • Functions using the speed signal disturbed (accessories, cruise control, shift indicator)
  • Check engine light depending on the maker

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–500
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

engine speed output circuittachometerengine control module

Related codes

P0335P0322P0655P0656U0155

References: law.cornell.edu, saabwisonline.com, saabwisonline.com.