What does it mean?
This is the same erratic-signal test applied to the B boost pressure sensor, the second pressure measuring point in the induction system on engines with two turbochargers or a two-stage arrangement. The module expects a clean, continuous pressure trace and rejects a signal that spikes, drops out or carries noise inconsistent with engine load.
Because the second sensor is often mounted further from the module and closer to hot pipework, harness and connector problems are even more likely here than on the A sensor. The fault is stored when the disturbance is large enough to affect boost control, and the software will normally fall back on the remaining pressure information to keep the engine running safely. Diagnosis has to catch the glitch while it happens, so live logging and a wiggle test do most of the work.
Symptoms
- Sudden short power drops during acceleration that clear on their own
- MIL that switches on and off between drives
- Uneven or surging boost delivery, sometimes with an audible change in turbo note
- Intermittent limp mode, often after driving on rough roads
- Live data spikes or dropouts on this sensor while the other pressure signals stay smooth
Likely causes
- Vibration-related loss of contact in the sensor connector, from spread or backed-out terminals
- Chafed or heat-damaged wiring near the charge pipe, exhaust or turbocharger housing
- Corrosion or moisture in the connector giving an intermittent conductive path
- Cracked sensor body or a fatigued sensing element that fails only when hot
- Contamination of the pressure port with oil, soot or water
- Poor or corroded ground connection for that sensor
- Intermittent break in the shared reference voltage circuit
- Electrical noise from a nearby failing component or badly installed accessory wiring
How to fix it
- Record both boost sensors together during a road test and identify which one is producing the glitch
- Wiggle the connector and the loom along the charge pipe with the engine running and watch for a signal disturbance
- Inspect the terminals for tension and corrosion, and reseat or replace any that are loose
- Check the ground circuit for voltage drop and clean any corroded ground point
- Verify the reference voltage remains steady while the engine is loaded
- Remove the sensor and clear its port of oil and condensate
- Reroute or protect any wiring lying against hot components, then replace the sensor only if the disturbance stays with the sensor itself