Turbocharger Overboost Condition

The opposite of P0299. The PCM saw actual boost go higher than the maximum allowed for the current RPM/load. This is dangerous — sustained overboost can crack pistons, blow head gaskets, and kill turbos. The PCM will pull power immediately when it sees this. Common causes are a wastegate stuck closed, a leaking wastegate vacuum/pressure line, or a failed boost control solenoid stuck commanding full boost.

Measured boost has exceeded the maximum allowed boost threshold for the calibrated time, usually triggering a torque cut.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 1Verify wastegate actuator rod moves freely by hand with the engine off.
2. 2Apply ~10 psi of shop air to the actuator — rod should extend and hold.
3. 3Inspect all boost reference and control lines for cracks or disconnects.
4. 4Test the boost control solenoid for proper switching.
5. 5Check for aftermarket tunes — these are the #1 cause on enthusiast vehicles.

• Wastegate stuck closed (rust, broken linkage)
• Disconnected or cracked wastegate reference line
• Boost control solenoid stuck (commanding no wastegate signal)
• Failed actuator diaphragm
• Aftermarket tune commanding too much boost

$50 (line) to $1,500 (actuator + labor).