What does it mean?
The turbocharger outlet pressure sensor sits after the compressor and reports how much pressure the charger is actually producing, which the module uses as feedback for wastegate or variable vane control and as protection against overboost. Sensor A is the primary unit on engines fitted with more than one. This code is the general circuit fault: the module cannot obtain a valid signal, and the cause lies in the reference, ground or signal path rather than in the pressure itself. With no usable feedback the boost control loop cannot close, so the module normally caps boost and limits power until the circuit is restored.
Symptoms
- MIL on with a clear loss of power, especially under load
- limp mode with boost held at a minimum on many vehicles
- No plausible boost pressure value on a scan tool, or a value stuck at a default
- Sluggish acceleration and hill or overtaking performance well below normal
- Black smoke on diesels when fuelling and airflow no longer match
- Turbocharger that stays quiet because the wastegate or vanes default to a safe position
Likely causes
- Open or short in the sensor reference, signal or ground wire
- Connector unplugged, partly seated or corroded by water entering from above
- Internally failed pressure sensor
- Harness chafed or melted where it runs close to a hot charge pipe or the turbocharger
- High resistance sensor ground or a corroded ground splice
- Terminals damaged or pushed back during previous work on the charge air system
- Rarely, a failed input pin or driver inside the control module
How to fix it
- Read the freeze frame and check whether the sensor value is missing, fixed or clearly out of range live
- With the key on and the engine off, compare the sensor reading with barometric pressure; a healthy sensor reads atmospheric
- Inspect the connector for corrosion, water, backed out terminals and heat damage
- Measure reference voltage and ground at the sensor connector, then check signal continuity back to the module
- Perform a wiggle test along the harness where it passes hot or moving parts
- Repair the damaged conductor or connector and re-route the harness away from heat sources
- Replace the sensor only after supply, ground and signal circuits are proven good