P0388 Crankshaft position sensor B signal too high

Crankshaft position sensor B circuit high input

P0388 in short

P0388 means the engine computer reports a high voltage problem with crankshaft position sensor B. The sensor, its wiring or its connector is the usual cause. Depending on the vehicle, the engine may start hard, run rough, stall or not start, so get it checked soon and avoid relying on the car until it is.

The crankshaft position sensor tells the engine computer how fast the engine turns and where the pistons are, so it can time fuel and spark. P0388 is set when the signal from crankshaft position sensor B is higher than expected.

TroubleCodes.net and the Delaware DMV list agree on the generic title: Crankshaft Position Sensor B Circuit High Input. The code points at the sensor B circuit but does not say which part failed.

Sensor, wiring and connector are the usual suspects, and the computer is checked last. Which engine is affected, and what 'B' refers to, depends on the maker, so use the vehicle's own service information.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Crankshaft position sensor malfunction

    Common general cause
    Why it ranks here
    TroubleCodes.net lists sensor malfunction alongside a short to positive and the engine computer.
    What would change this
    Rises if the sensor tests open, shorted or gives no signal while cranking. Falls if the sensor tests normal.
    How to test the crankshaft position sensor

  2. Damaged wiring or connector between the sensor and the computer

    Common general cause
    Why it ranks here
    TroubleCodes.net lists harness damage, corrosion and loose or contaminated connectors for this code.
    What would change this
    Rises if the harness is chafed, corroded or wiggling it changes the signal. Falls if the circuit tests clean end to end.

  3. Engine computer failure

    Possible — needs testing
    Why it ranks here
    TroubleCodes.net lists the engine computer last.
    What would change this
    Rises if the sensor and wiring test normal. Falls if either shows a fault.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored codes and freeze-frame data with a scan tool, and note any other crankshaft or camshaft codes stored with P0388.

    Low riskTool: OBD-II scan tool

    • IfOther crank or cam codes are stored

      It meansThe wiring or computer may be involved; note them for the shop.

      Go to step 2

    • IfOnly P0388 is stored

      It meansLook at the sensor wiring next.

      Go to step 2

  2. With the engine off, inspect the crankshaft sensor connector and visible harness for damage, corrosion, oil or coolant contamination and loose pins.

    Low risk

  3. Have the sensor resistance and signal checked against the maker's specification, and have the harness tested for opens and shorts.

    Best left to a shopTool: multimeter, oscilloscope

    Warning:The signal is checked while the engine is cranked, close to belts and fans, and the sensor is often in a hard-to-reach spot near the transmission. Let a shop do it.

Symptoms

  • Check engine light on
  • Engine may crank without starting or stall

How to fix

  1. With the engine off, look over the crankshaft sensor connector and visible wiring for damage or corrosion.

Parts and cost context

  • Crankshaft position sensor:Test the sensor and wiring before replacing it. The sensor can be hard to reach, so labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

We don't have reviewed vehicle-specific evidence for P0388 yet. The causes and tests above apply across vehicles.

  • P0385Crankshaft position sensor B circuit malfunction

    Same system Possible — needs testing

    P0385 is the circuit malfunction code for the same crankshaft sensor B circuit.

All Ignition and engine position sensors codes

Sources and review

  1. P0388 trouble code — TroubleCodes.net
  2. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
Editorial review
Pending
Technician review
Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

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Used once to identify your engine; not stored.