OBD-II Code P0240 — What It Means & How to Fix It

What Does This Error Mean?

P0240 means the PCM detected a problem with the turbocharger boost pressure sensor B circuit. Sensor B is typically found on turbocharged engines with two turbo stages or banks. The PCM uses boost pressure data to control fueling and boost levels. You may notice reduced power, over-boost, or under-boost conditions.

Affected Models

All 1996+ turbocharged vehicles with dual boost sensors
Common in Ford EcoBoost engines (2.0T, 2.3T, 3.5TT)
Common in Dodge/Chrysler diesel and gas turbocharged engines
Common in BMW and Audi twin-turbocharged engines
Common in diesel trucks with compound or staged turbocharger systems

Common Causes

Failed turbo boost pressure sensor B with an out-of-range or missing signal
Damaged, corroded, or broken wiring in the boost sensor B signal circuit
Cracked or disconnected vacuum/pressure hose leading to the sensor
Moisture or debris contamination inside the sensor or its hose
Poor connection at the boost sensor B harness connector

How to Fix It

Use an OBD-II scanner with live data to check the boost sensor B pressure reading at idle. It should show close to atmospheric pressure (around 14.7 PSI or 0 kPa of boost). An erratic or flat zero reading indicates a sensor or circuit problem.

Compare the live readings of sensor A and sensor B if your scanner shows both. They should match closely under the same conditions.
Locate the boost pressure sensor B on your engine. It is usually threaded into the intake manifold, intercooler pipe, or turbo outlet. Inspect the vacuum or pressure hose that connects to it. Look for cracks, splits, or hoses that have come loose.

A disconnected boost hose is a very common cause of boost sensor codes and takes only seconds to check and fix.
Inspect the sensor wiring harness connector for corrosion, bent pins, or looseness. Unplug it, spray with electrical contact cleaner, and reconnect firmly. Check the wiring back toward the PCM for any visible damage.

Boost sensor wiring on turbocharged engines is often routed near hot components. Heat damage to wire insulation is common.
Test the sensor supply voltage. With the ignition on and the sensor unplugged, check for 5 volts on the reference wire and a clean ground on the ground wire. No voltage means the fault is in the wiring, not the sensor itself.

Most MAP and boost sensors use a 5-volt reference signal. Confirm with your service manual for the exact pin layout.
Replace the boost pressure sensor B if all wiring and hose connections check out. Clear the stored fault codes and perform a test drive under load to confirm the boost readings are now correct and no codes return.

Sensors are usually inexpensive. When in doubt, replacing the sensor is a reasonable step after eliminating wiring and vacuum hose issues.

When to Call a Professional

If replacing the sensor and checking hoses does not resolve the code, the wiring or PCM needs professional testing. A shop can check sensor signal voltage with a scan tool and perform a circuit continuity test. Diagnosis typically costs $80-$130. Boost pressure sensor replacement usually runs $80-$200 depending on the vehicle.

Frequently Asked Questions

What does boost sensor B mean compared to sensor A?

Turbocharged engines with two turbo stages or banks use two boost sensors. Sensor A monitors the first stage or primary bank. Sensor B monitors the second stage or secondary bank. P0240 applies to the B sensor circuit only.

Will P0240 cause limp mode?

It can, depending on the vehicle. If the PCM cannot reliably measure boost pressure, it may reduce power as a safety measure. This prevents over-boosting, which can damage the engine. Expect reduced performance until the fault is resolved.

Can a loose vacuum hose cause P0240?

Yes, absolutely. The boost sensor relies on a direct pressure connection to measure boost levels. A cracked or loose hose gives the sensor an incorrect reading or no reading at all. Always check hoses first — it is the easiest and cheapest thing to inspect.