P0388 Crankshaft Position Sensor B Circuit High Input

P0388 points to a high input condition in Crankshaft Position Sensor B circuit. The crank B signal voltage is higher than expected or stuck high.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the crank sensor before checking ground integrity and short-to-voltage faults in the B circuit.

Symptoms of P0388

Rough idle, shaking, or a stumble under acceleration.
A flashing check-engine light during an active misfire.
Power loss and higher fuel consumption.

Common causes of P0388

Worn spark plugs, ignition coils, or plug wires.
Fuel-delivery problems — injectors, pressure, or a lean/rich mixture.
Vacuum leaks, low compression, or a mechanical fault in that cylinder.

Useful checks before replacing parts

Review crank B signal voltage, reference voltage, ground quality, freeze-frame RPM, and other high-input or reference-voltage codes.
Inspect for open grounds, short-to-voltage faults, connector corrosion, damaged shielding, wiring insulation damage, and sensor contamination.
Scope the signal during cranking and running to see whether it toggles normally or stays biased high.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.