What does it mean?
The signal voltage from the B turbocharger outlet pressure sensor has fallen below the lowest value the module accepts as valid, typically a few tenths of a volt. A three-wire pressure sensor should never report near zero volts even at atmospheric pressure, because its output is biased upward by design so that a broken circuit can be recognised. A reading pinned at the bottom of the scale therefore means the signal has been pulled to ground, the five volt supply has been lost, or the sensor has failed internally. The module cannot use a value it knows to be invalid, so it substitutes a default boost figure and restricts turbocharger output. The fault sets quickly, often within seconds of the key being turned on.
Symptoms
- MIL on, usually straight after starting the engine
- Marked loss of power and often limp mode, because the module assumes a safe low boost value
- Live data showing zero or near-zero pressure even with the engine off, when it should read atmospheric
- Poor throttle response and slow acceleration
- Other sensors reading implausibly low at the same time if the shared reference has been lost
Likely causes
- Signal wire shorted to ground, frequently where the loom is clamped against the engine or a charge pipe bracket
- Open five volt reference feeding the sensor, which drops the output to zero
- Water or salt in the connector bridging the signal pin to the ground pin
- Internally failed sensor with a shorted output stage
- Broken or crushed wire inside the loom after previous repair work in the engine bay
- Sensor connector not fully latched after an intercooler or charge pipe removal
- Failed reference supply inside the control module, which normally affects several sensors at once
How to fix it
- Look at the live value with the key on and the engine off; a healthy sensor must read close to barometric pressure, so zero here confirms the fault is real
- Unplug the sensor and check for five volts on the reference pin; no voltage means the problem is upstream of the sensor
- With the connector unplugged and the key on, check the signal pin at the module end; if it now reads high, the wiring or sensor was pulling it to ground
- Test the signal wire for a short to ground along its full length and inspect the loom where it is routed near hot or moving parts
- Inspect the connector for corrosion, moisture and pushed-back terminals
- Repair the reference or signal circuit as required, then fit a new sensor only if the wiring proves good
- Clear the code and verify the reading matches barometric pressure at key-on and rises correctly under load