Faulty crankshaft position sensor B (internal fault or failed electronics); Damaged wiring to the sensor, such as a short to voltage or an open circuit in the signal or ground wire; Corroded, loose or contaminated connector at the sensor or control unit; Poor ground or reference supply fault affecting the sensor circuit; Damaged or contaminated reluctor or trigger wheel, or incorrect air gap or sensor fitting; Electrical interference from nearby high-tension or charging system faults; Fault within the engine control unit.

P0388

Crankshaft Position Sensor B Circuit High.

Generic
Powertrain
Generic code
High severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
3: AreaIgnition system or misfire
88: FaultThe specific fault in that area

What it means

P0388 is the generic SAE J2012 code for Crankshaft Position Sensor B Circuit High. The engine control unit has seen a voltage or signal on the secondary crankshaft position sensor circuit that is higher than expected, which points to a short to voltage, an open circuit that lets the signal float high, or a sensor fault. The exact sensor referred to as 'B' and its location depend on the model and engine.

Symptoms

Engine cranks but is slow to start or fails to start
Intermittent stalling or cutting out while running
Misfires or rough running
Hesitation and loss of power
Check engine light on, possibly with limp mode
Rev counter erratic or not working on some vehicles

Possible causes

Faulty crankshaft position sensor B (internal fault or failed electronics)likely
Damaged wiring to the sensor, such as a short to voltage or an open circuit in the signal or ground wirelikely
Corroded, loose or contaminated connector at the sensor or control unitlikely
Poor ground or reference supply fault affecting the sensor circuitpossible
Damaged or contaminated reluctor or trigger wheel, or incorrect air gap or sensor fittingpossible
Electrical interference from nearby high-tension or charging system faultsrare
Fault within the engine control unitrare

How to diagnose

Read all stored and pending codes and note any related crankshaft, camshaft or misfire codes, then review the freeze frame data
Check the live data for engine speed signal while cranking and running, and compare it with the other position sensor if fitted
Visually inspect the sensor, its wiring harness and connector for chafing, heat damage, oil contamination, corrosion and bent or pushed-back pins
Confirm sensor B location and type using model-specific information, as it varies between engines
Check the sensor mounting, air gap and condition of the reluctor or trigger wheel for damage or debris
With the connector unplugged, test the supply, signal and ground circuits for shorts to voltage, open circuits and high resistance, using the manufacturer's specification
Check the sensor output with a suitable meter or oscilloscope while cranking and compare it with a known good pattern
Wiggle-test the harness with the engine running or cranking to find intermittent faults

How to fix

Replace the crankshaft position sensor B if it fails testing
Repair or replace damaged wiring, correcting any short to voltage or open circuit
Clean or replace corroded or damaged connectors and terminals
Restore the proper ground or supply to the sensor circuit
Refit the sensor correctly, or replace a damaged reluctor or trigger wheel as required
Clear the code and road test after repair to confirm it does not return

Can I keep driving?

High severity

Avoid driving if you can, as the engine may stall without warning, which is a safety risk, especially in traffic. If the car is running normally, only drive it a short distance to a workshop.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.