Faulty boost pressure sensor B (internal fault giving a high signal); Signal wire shorted to the sensor supply or another voltage source; Open circuit or poor connection in the sensor ground wire; Corroded, loose or damaged sensor connector terminals; Sensor reference supply voltage too high due to a wiring or control unit supply fault; Blocked or split pressure or vacuum line to the sensor, where the design uses one; Faulty engine control unit.

P0242

Turbocharger/Supercharger Boost Sensor B Circuit High.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
2: AreaFuel and air metering (injector circuit)
42: FaultThe specific fault in that area

What it means

P0242 is the generic SAE J2012 code for a high input from the circuit of turbocharger or supercharger boost sensor B. The engine control unit saw the sensor signal voltage rise above the expected range, which usually points to a short to voltage, an open ground or a faulty sensor. Which sensor is 'B' and where it sits depends on the model and engine, so check the manufacturer's data.

Symptoms

Engine warning light on
Reduced power or limp mode
Poor or surging acceleration
Black smoke or rich running in some cases
Boost gauge or live data reading implausibly high or stuck
Hesitation under load

Possible causes

Faulty boost pressure sensor B (internal fault giving a high signal)likely
Signal wire shorted to the sensor supply or another voltage sourcelikely
Open circuit or poor connection in the sensor ground wirelikely
Corroded, loose or damaged sensor connector terminalspossible
Sensor reference supply voltage too high due to a wiring or control unit supply faultpossible
Blocked or split pressure or vacuum line to the sensor, where the design uses onerare
Faulty engine control unitrare

How to diagnose

Read all stored codes and freeze frame data, noting engine load, rpm and boost at the time the fault set, and check for related sensor or boost control codes.
Check live data with the ignition on and engine off: the boost sensor should read close to ambient pressure. A reading far above that suggests a sensor or circuit fault.
Visually inspect the sensor, connector and wiring for chafing, heat damage, oil contamination, corrosion and bent or pushed-back pins.
Check any pressure or vacuum hose to the sensor for splits, blockages or oil build-up, if fitted.
With the connector unplugged, measure the reference supply and ground against the manufacturer's specification.
Check the signal wire for a short to voltage and for continuity back to the control unit, with the ignition off and the control unit disconnected where specified.
Wiggle test the harness with live data on screen to find intermittent faults.
If the wiring and supply are good, test or substitute the sensor following the manufacturer's procedure before suspecting the control unit.

How to fix

Replace the boost pressure sensor B if it fails testing.
Repair or replace any wiring that is shorted to voltage or has an open ground.
Clean or repair connector terminals, or renew the connector if it is damaged or corroded.
Clear or replace blocked or damaged pressure lines to the sensor where fitted.
Rectify the cause of any incorrect reference supply voltage, following manufacturer diagnostics.
Only after all other causes are ruled out, repair or replace the control unit as the manufacturer directs.

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, but it may go into limp mode with reduced power. Get it checked soon, as incorrect boost control can strain the engine and turbocharger.

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