Diagnostic: Loss of power on Mercedes-Benz - Causes and prices

Loss of power on a Mercedes-Benz (A-Class, C-Class, E-Class, GLA, GLC) shows as sluggish acceleration, poor pickup or lack of torque. Depending on turbo petrol or diesel (OM 654, OM 656) engines, common causes and repair costs differ.

Mercedes petrol (M 264, M 254)

On M 264 and M 254 (turbo petrol) engines, loss of power is often linked to the turbo (leak, wastegate), a faulty MAF sensor or a clogged injection system. A faulty lambda sensor or degraded catalyst can limit performance. Worn spark plugs and coils can cause misfires.

A clogged air filter reduces air supply and can be enough to drop power; replacement is low cost and worth checking first.

Mercedes diesel (OM 654, OM 656)

On OM 654 and OM 656 engines, loss of power is frequently linked to a saturated particulate filter (DPF) or the AdBlue system (level, injector, quality). A faulty turbo or clogged EGR valve also limit pickup. Faulty or clogged injectors cause incomplete combustion and a drop in power.

A forced DPF regeneration can be attempted in the workshop; if blockage is too severe, DPF cleaning or replacement will be needed.

What to do

Avoid heavy load until the cause is identified. An electronic diagnostic (fault codes) and checks of the turbo, DPF and MAF sensor help pinpoint the cause.

Order of magnitude for costs

• MAF sensor: about €150–400.
• Turbo: about €1,200–2,800 depending on engine.
• EGR valve: about €400–900.
• DPF regeneration / AdBlue diagnostic: about €80–200.
• DPF replacement: about €1,000–2,200.
• Diesel injector: about €400–800 per injector.

My Auto Check-up helps you prepare your visit by describing symptoms for an initial estimate. See also our check engine light and black smoke pages for Mercedes, or BMW and Audi for comparable brands.