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P0299 – Turbocharger Underboost – OM651 / OM642 (Mercedes-Benz OM651)

Fault code P0299 means "Turbocharger Underboost – OM651 / OM642". It is common on OM651 (C/E/GLK 200–250 CDI, Sprinter, Vito), OM642 V6 CDI (E/ML/GL/S 280–350 CDI, Sprinter 3.0) engines. Below are the real-world causes, step-by-step tests and OEM part numbers.

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P0299 quick summary

Fault codeP0299
MeaningTurbocharger Underboost – OM651 / OM642
SystemPowertrain (Engine & Transmission)
VehiclesMercedes-Benz
Common onOM651 (C/E/GLK 200–250 CDI, Sprinter, Vito), OM642 V6 CDI (E/ML/GL/S 280–350 CDI, Sprinter 3.0)
SeverityHigh
Can I drive?Yes, but usually in limp mode. Avoid heavy loads until it is repaired.
Repair cost€30 – €3,000

Symptoms of P0299

  • Limp mode and loss of power
  • Check Engine light
  • Hissing under load (boost leak)
  • Power returns after restarting
  • Sometimes P2563 or actuator codes alongside

Most common causes of P0299 (most likely first)

Mechanic's Pro Tip

On the OM642 the turbo's electronic actuator (on top of the turbo) is a well-known failure: its internal gear wears and it can no longer move the vanes properly. On the OM651 split or loose charge-air hoses and faulty boost control valves are common. Check the actuator movement and the charge-air system before you replace the whole turbo.

  1. 1.Faulty electronic turbo actuator (OM642)

    Most likely

  2. 2.Split or loose charge-air hose or intercooler leak

  3. 3.Faulty boost pressure control valve or vacuum actuator (OM651)

  4. 4.Sticking turbo vanes or bypass flap

  5. 5.Worn turbocharger

Step-by-step diagnostic guide

  1. 1

    Read all codes with XENTRY or a Mercedes-capable scanner; note actuator and position codes.

  2. 2

    Compare specified and actual boost during a full-load drive.

  3. 3

    Pressure-test the charge-air system and inspect hoses and intercooler.

  4. 4

    Run the turbo actuator test and watch the linkage; on vacuum versions test the actuators with a hand pump.

  5. 5

    Check turbo shaft play; replace or recondition the actuator or turbo as needed and calibrate the actuator.

Frequently asked questions

Can the OM642 turbo actuator be replaced separately?

Yes. Reconditioned and new electronic actuators are available; after fitting they must be calibrated to the turbo. It is much cheaper than a complete turbo if the turbo itself is fine.

How much does it cost to fix P0299 on a Mercedes diesel?

A charge-air hose or valve costs from about 30–150 €. An electronic actuator costs a few hundred euros; a reconditioned turbo about 800–2,000 € fitted, more for twin-turbo versions.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.