What does it mean?
The module has found an electrical fault in the circuit of the B turbocharger outlet pressure sensor. This sensor is fitted in the pressurised pipework immediately after the compressor housing and reports how much pressure the turbocharger is actually producing before the charge air cooler and the throttle.
Its signal is used for boost control, for protecting the engine against overboost and for cross-checking the manifold pressure sensor, and on a twin-turbo or a two-stage system the B sensor covers the second measuring point. The module supplies a five volt reference and a ground and expects the returned signal to stay within a defined electrical band; a value outside that band, or a circuit that cannot be read at all, sets this code.
Boost control is normally moved to a conservative default while the fault is present.
Symptoms
- MIL on, often with reduced power or limp mode as the module falls back to a safe boost strategy
- Noticeably slower acceleration and lower top-end pull
- Boost readings in live data that do not match what the engine is actually doing
- Occasional surging or hesitation under load
- Other sensor codes appearing at the same time if the shared reference circuit is at fault
Likely causes
- Corroded, damp or loose connector at the sensor, which sits in a hot and vibration-heavy area
- Chafed or heat-damaged wiring in the section of loom running along the charge pipe
- Open or shorted five volt reference, which usually affects other sensors sharing the same feed
- Open or high-resistance sensor ground
- Failed pressure sensor with an internally open or shorted element
- Oil, soot or condensate blocking the sensor port so it cannot see pressure, which often appears as an implausible circuit reading
- Damaged module connector or, rarely, a failed reference supply inside the module
How to fix it
- Read all stored codes first; a group of sensor faults together points at a shared reference or ground problem rather than this sensor
- With the key on and the engine off, compare the sensor reading with barometric pressure; a healthy sensor should read close to ambient
- Unplug the connector and check for five volts on the reference pin and a clean ground on the return pin
- Inspect the connector for corrosion, spread terminals and oil contamination, and follow the loom for chafe and heat damage
- Measure the signal wire back to the module for continuity and for shorts to ground or voltage
- Remove the sensor and check that its port and tip are free of oil and carbon
- Fit a new sensor only after the circuit is proven, then verify that the reading tracks manifold pressure sensibly during a road test