Fuel and air

P02CB — Turbocharger/Supercharger B Underboost Condition

Severity: medium Drive with care, to a shop

What P02CB means

P02CB means actual boost pressure in the second turbocharger or supercharger circuit (B) is lower than what the ECU requested. The ECU normally compares the boost pressure sensor reading with a target value and controls boost through a wastegate or variable geometry actuator. When boost stays too low, it stores this code and may limit engine power.

Symptoms

  • Check Engine light on
  • Reduced power and sluggish acceleration
  • Boost pressure lower than expected on a scan tool
  • Unusual whistling or whining from the turbo
  • Limp mode with limited power

Possible causes

  1. Air leak in the intake or intercooler piping (most likely)
  2. Stuck or faulty wastegate or actuator
  3. Faulty boost pressure sensor
  4. Mechanical turbocharger failure
  5. Faulty control solenoid or variable geometry actuator
  6. Sticking variable geometry mechanism
  7. Vacuum leak in the control lines
  8. Wiring damage or poor connector contact

How to diagnose

  1. Read all codes and freeze frame data, and note any related codes
  2. Inspect boost hoses, clamps and the intercooler for cracks, oil residue and loose joints
  3. Check the air filter and intake path for restriction
  4. Compare commanded and actual boost on a scan tool
  5. Check actuator movement over its full range and inspect vacuum lines
  6. Test the boost pressure sensor's power, ground and signal
  7. Inspect wiring and connectors for the actuator and sensors
  8. Check turbo shaft play and vane condition

Common fixes

  • Replace damaged boost hoses and tighten clamps
  • Replace a faulty boost pressure sensor
  • Clean, repair or replace the wastegate actuator or solenoid
  • Repair or replace the turbocharger
  • Repair wiring and connectors

Questions and answers

What does P02CB mean?

The boost pressure on turbo or supercharger B is below the ECU's target. Common causes are air leaks, a wastegate actuator problem or a bad boost sensor.

Can I drive with code P02CB?

Only carefully and for a short time, since power will be reduced. If you hear odd turbo noises, stop and have it checked.

How do I find the cause of underboost?

Start by checking the hoses and intercooler for leaks, then compare commanded and actual boost on a scan tool and test the actuator's movement.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.