What should a mechanic test for loss of power?
A useful test plan for loss of power verifies the operating state first, preserves scan evidence, and measures the competing engine & drivability paths before any component is replaced.
Plausible causes
- Engine operating-state fault
- Fuel, air, or ignition delivery
- Mechanical compression or timing
Useful next checks
- Battery and cranking voltage-drop test
- Full-module scan with freeze-frame and cranking RPM
- Fuel pressure, spark, injector pulse, and fuel-trim tests
- Compression, leak-down, and cam/crank correlation when supported
Related OBD codes
Sources and method
This answer provides hypotheses and a verification plan, not a component verdict. Exact repair procedures require authoritative service information for the specific vehicle.
Engine Misfire Diagnostic Aid · NHTSA / Volkswagen