Diagnostic Trouble Code

P2633

Charge Air System Offset Drift Under Engine Load — Mercedes CDI

What the code means

The Mercedes engine-management system has detected a discrepancy in the charge-air system under load.

On the Mercedes CDI application covered here, 2633/P2633 is reported as Charge Air System Offset Drift Under Engine Load.

The fault can be accompanied by a severe loss of power or limp-mode behaviour because the engine-management system no longer considers the charge-air values plausible under load.

This Speed Tweaks case involved a Mercedes 2.2 CDI with extremely poor performance and effectively no boost. After the physical system had been considered, initialization of the air-intake and turbocharging adaptations restored correct operation.

That does not mean every Mercedes with 2633 simply needs its adaptations reset. Air leaks, sensor plausibility problems and other physical faults must still be considered before treating initialization as the repair.

Possible causes

What could cause this P2633 fault?

Charge-air or intake-system leak

Air-mass measurement discrepancy

Boost-pressure measurement discrepancy

Intake or boost sensor plausibility problem

Wiring or connector fault

Air-filter or intake restriction

Turbocharger control or actuator problem

Air-intake or turbocharging adaptations requiring initialization

Diagnostic approach

What should you check?

1. Confirm the Mercedes fault description. Make sure the diagnostic equipment reports the charge-air offset-drift interpretation of 2633/P2633 rather than the generic OBD-II fuel-pump definition.
2. Read the complete fault memory. Look for related boost-pressure, airflow, intake, EGR or actuator faults that may help explain why the charge-air values are implausible.
3. Check the physical air system. Inspect the intake and charge-air system for leaks, restrictions, damaged hoses or other faults that could cause the measured airflow and boost values to disagree.
4. Check live data and sensor plausibility. Compare relevant airflow, pressure and boost information and establish whether the values make sense for the engine's operating conditions.
5. Check turbocharger control. Establish whether the turbocharger actuator or control system is operating correctly rather than assuming the turbocharger itself has failed.
6. Consider adaptation initialization. If the physical system and relevant signals have been verified, use suitable diagnostic equipment to check whether the Mercedes air-intake and turbocharging system adaptations require initialization.
7. Verify the result under load. Clear the relevant faults as appropriate, road-test the vehicle and confirm that boost, actuator operation and engine performance have returned correctly.

Speed Tweaks diagnostic video

Watch this P2633 diagnosis in the workshop

This Speed Tweaks video follows a real-world P2633 fault and shows the diagnostic process in practice.

Watch on YouTube →

A useful thing to remember

The adaptation reset fixed the vehicle in this Speed Tweaks case, but a successful repair on one vehicle is not a substitute for diagnosis. Prove the physical system is sound first.