What causes fault code P02CB?

• Most likely: Boost leaks in the induction system (intercooler, hoses, or cracked intake components) • Likely: Faulty boost pressure control solenoid (Wastegate control valve) • Possible: Sticking Wastegate actuator arm or Variable Geometry Turbo (VGT) vanes • Rare: Faulty boost pressure sensor or restricted exhaust/clogged DPF (Diesel Particulate Filter)

How do you fix fault code P02CB?

STEP 1: Perform a smoke test or boost leak test on the induction system to identify leaks. Inspect all hose clamps. STEP 2: Inspect vacuum lines to the boost control solenoid. Measure solenoid resistance (typically 15-30 Ohms depending on application). STEP 3: Verify that the Wastegate or VGT actuator arm moves freely. On vacuum-actuated systems, use a hand-held vacuum pump to ensure the diaphragm holds vacuum and moves at approx 5-10 inHg. STEP 4: Log live data for boost pressure. Desired vs. Actual boost should track closely within 0.1-0.2 bar.

Powertrain (Engine & Gearbox)Standard EOBD

P02CB - Turbocharger/Supercharger 'B' Underboost Condition

Q: What are the symptoms of fault code P02CB?

• Check engine light (MIL) illuminated • Significant loss of engine power (Limp home mode) • Abnormal hissing or whistling noises during acceleration • Increased fuel consumption • Black smoke from exhaust (on diesel engines)

Last updated:1 February 2026

Related:Turbocharger, Boost Pressure Sensor, Wastegate, Intercooler, MAP Sensor

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0200

Injector Circuit Malfunction

P0201

Cylinder 1 Injector Circuit Open

P0202

Injector Circuit - Cylinder 2 - Malfunction

P0203

Injector Circuit - Cylinder 3

Technical Description

P02CB is stored when the Engine Control Module (ECM) detects that the boost pressure from the secondary turbocharger or supercharger (designated 'B') is below the commanded setpoint for target load conditions. The ECM monitors pressure via the Manifold Absolute Pressure (MAP) or Boost Pressure sensor. If actual boost remains below the target (typically >2-4 psi deviation for more than 5 seconds), the code sets. This directly affects the engine's volumetric efficiency and performance.

Possible Causes

Boost leaks in the induction system (intercooler, hoses, or cracked intake components)

Faulty boost pressure control solenoid (Wastegate control valve)

Sticking Wastegate actuator arm or Variable Geometry Turbo (VGT) vanes

Faulty boost pressure sensor or restricted exhaust/clogged DPF (Diesel Particulate Filter)

Symptoms

Check engine light (MIL) illuminated

Significant loss of engine power (Limp home mode)

Abnormal hissing or whistling noises during acceleration

Increased fuel consumption

Black smoke from exhaust (on diesel engines)

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P02CB - Turbocharger/Supercharger 'B' Underboost Condition

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P02CB - Turbocharger/Supercharger 'B' Underboost Condition

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