Damaged, chafed or corroded wiring to the boost sensor (open circuit, short to earth or short to supply); Loose, corroded or contaminated sensor connector pins; Faulty boost pressure sensor B; Blocked, split or disconnected sensor pipe or hose, or oil contamination in the sensor port; Fault in the sensor 5 volt reference supply or earth shared with other sensors; Boost leak or turbo fault causing a signal that does not match expected values; Fault inside the engine control unit.

P0239

Turbocharger/Supercharger Boost Sensor B Circuit.

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)
39: FaultThe specific fault in that area

What it means

P0239 is the generic code for a fault in the circuit of turbocharger or supercharger boost sensor B. The engine control unit has seen a signal from this sensor that is out of range, stuck, erratic or missing, or that does not agree with other sensors such as the barometric or manifold pressure readings. Which sensor counts as 'B' and where it is fitted depends on the engine and model.

Symptoms

Engine management warning light on
Reduced power or limp mode with boost limited
Poor acceleration or hesitation under load
Black smoke or rich running in some cases
Erratic or no boost reading on a scan tool
Turbo overboost or underboost codes alongside it

Possible causes

Damaged, chafed or corroded wiring to the boost sensor (open circuit, short to earth or short to supply)likely
Loose, corroded or contaminated sensor connector pinslikely
Faulty boost pressure sensor Blikely
Blocked, split or disconnected sensor pipe or hose, or oil contamination in the sensor portpossible
Fault in the sensor 5 volt reference supply or earth shared with other sensorspossible
Boost leak or turbo fault causing a signal that does not match expected valuespossible
Fault inside the engine control unitrare

How to diagnose

Read all stored codes and freeze frame data, noting engine load, speed and boost at the time the fault set, and check for related codes such as other sensor supply or boost control faults
Identify which sensor is 'B' for this specific engine using the manufacturer's data, as location and naming vary by model
Visually inspect the sensor, connector and wiring for chafing, heat damage, oil, water ingress and bent or corroded pins
Check the sensor pipe or hose and the sensor port for splits, blockages, looseness or oil contamination
Compare live boost sensor B readings with the barometric reading at key on, engine off, and with other pressure sensors, then watch for plausible change under load
Using the wiring diagram, test the sensor 5 volt supply, earth and signal wire for continuity, shorts and correct voltage
Wiggle test the harness and connector with the engine running while watching the live data for dropouts
Check the intake and charge air system for leaks and check turbo operation if readings are plausible but boost does not match demand

How to fix

Repair or replace damaged wiring and fix any shorts or open circuits
Clean or replace corroded connector terminals or the connector
Replace the boost pressure sensor B if it fails testing
Replace or clear blocked or split sensor hoses and clean the sensor port
Repair charge air leaks or address turbo faults found during testing
Repair or replace the control unit only after all wiring, supply and sensor faults are ruled out

Can I keep driving?

Medium severity

The car can usually be driven carefully for a short time, often in limp mode with reduced power, but it should be fixed soon. Avoid heavy loads and hard acceleration, and stop if the engine runs badly or other warnings appear.

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