Engine

P0388 — Crankshaft Position Sensor 'B' Circuit High Input

Severity: high Drive with care, to a shop

What P0388 means

The engine control module constantly monitors the signal from crankshaft position sensor 'B'. That signal tells it engine speed and crank position, which it needs to time spark and fuel injection correctly. P0388 sets when the circuit voltage is higher than expected, for example from a short to power, an open circuit or a failed sensor.

Symptoms

  • Check Engine light is on
  • Rough or unstable idle
  • Misfires and hesitation
  • Engine stalls while driving or at stops
  • Reduced power and sluggish acceleration
  • Hard starting or no-start

Possible causes

  1. Failed crankshaft position sensor 'B'
  2. Damaged wiring or corroded connector at the sensor
  3. Signal wire shorted to battery voltage
  4. Poor ground or bad reference voltage to the sensor
  5. Open circuit in the signal or ground wire
  6. Internal PCM input circuit fault (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data, and look for related crankshaft or camshaft sensor codes
  2. Inspect the sensor, connector and harness for chafing, oil, corrosion and bent pins
  3. Make sure the connector is fully seated and free of water
  4. Use a multimeter to check reference voltage and ground at the sensor connector, following the wiring diagram for your vehicle
  5. Test the signal wire for a short to power or an open circuit with the PCM connector unplugged
  6. Test the sensor itself by checking resistance or viewing the signal on a scope while cranking
  7. Check the sensor air gap and the condition of the reluctor wheel or tone ring
  8. If wiring and sensor are good, check PCM power and the input circuit

Common fixes

  • Replace crankshaft position sensor 'B'
  • Repair damaged wiring and replace the connector or terminals
  • Fix the signal wire short to voltage
  • Clean and restore ground and reference circuit connections
  • Repair or replace the PCM if the fault is confirmed there

Questions and answers

What does P0388 mean?

The PCM detected too high a voltage in the crankshaft position sensor 'B' circuit. The cause is usually the sensor, its wiring or the connector.

Can I drive with P0388?

It's best not to. The engine can stall at any time and then refuse to restart, which is dangerous in traffic.

Will replacing the sensor fix it?

Not always. Check the wiring, connector and sensor supply first, because a short to power can damage even a new sensor.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.