Why your Mercedes is stuck in limp mode

Which Mercedes cars are affected?

This page covers limp mode and loss of power caused by turbo, boost and intake faults on turbocharged Mercedes engines. Two groups of cars have DVSA recalls in this area:

• C-Class and E-Class cars built August to December 2011: a charge-air hose recall
• E-Class cars built May 2018 to May 2019: a turbo oil feed pipe recall

A gearbox fault can also put a Mercedes into limp mode. That is a different repair, so the first thing we check is which system has reported the fault. For other Mercedes work, see our Mercedes specialist page.

What are the symptoms?

The usual signs are:

• loss of power and poor acceleration
• the engine warning light
• the car running in emergency mode

When you book, tell us when it happens, for example under hard acceleration or uphill, whether it clears after the engine is restarted, and which warning lights are on.

What causes it?

On the engine side, one cause is a fault in boost control, the system that controls the pressure the turbo delivers. Known causes include:

• soot or stiffness in the turbo’s vanes, which overloads the electronic actuator that moves them
• corrosion or damage to the turbo or actuator
• a cracked charge-air hose, which lets boost pressure escape

How do you confirm the cause before fitting parts?

A fault code is not a repair, and a turbo is not condemned on a code alone. Before we quote for any parts, we:

• read the fault codes and check which system stored them
• run an actuator test
• watch the live boost values against what the engine is asking for
• check the turbo and the charge-air hoses visually

We then show you what we found and send a written price. No part is fitted until you approve it in writing.

What does the repair involve?

The repair depends on what the tests find. A cracked hose is replaced. Where the turbo or its actuator is at fault, the turbo and its electronic actuator are matched as a unit, so a replacement is set up and adjusted after fitting.

Once the work is done, we check that the power has returned and verify the repair, including a road test where appropriate.

How long does a limp mode repair take?

It depends on what the tests find, because a hose and a turbo are very different repairs.

Before any work starts, you get a written price and a promised time for your next update. If the car needs to stay with us, ask about a courtesy car when you book.

Is there a recall to check?

The DVSA lists these recalls that relate to boost and the turbo:

• R/2012/159: charge-air hose, C-Class and E-Class built August to December 2011
• R/2020/048: turbo oil feed pipe, E-Class built May 2018 to May 2019

Whether a recall applies depends on the individual car, so check your registration on gov.uk. Mercedes-Benz UK’s own vehicle check also shows non-safety service measures. Recall work is done by the manufacturer’s network, not by us.