P2CB8 Turbocharger/Supercharger Boost Pressure B Too High - Mechanical

P2CB8 reports that the second charger, B, produces more boost than the engine module allows, and attributes this to a mechanical cause such as a wastegate or bypass of charger B that no longer opens, a seized actuator rod or sooted variable vanes stuck in the closed position. It is the B twin of P226B. No manufacturer documents P2CB8 publicly. GM's A-side performance check on 2018 diesels watches the same overboost direction with a barometric correction and lists exhaust restrictions as a trigger. CARB requires overboost detection on boosted engines. Unlike P02CA, which only notes boost above target, P2CB8 points at hardware. To protect the turbine and engine, the module usually cuts torque or opens a relief path.

Likely causes

Symptoms

• Sudden power cut under full load
• MIL on
• Surging or jerky boost build-up

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, gsi.ext.gm.com.