6 cylinders. Big
AO Silver Member
Join Date: Jun 2009
Location: United Kingdom
County: West Midlands
When the ECU senses an issue, could be EGR, DPF or pretty much any electrical or mechanical issue, it goes into Limp Mode. This is where the ECU protects the rest of the system by restricting the power output of the engine, reducing boost etc..
It can be reset by turning the car on and off, but it will return when the sensors tell the ECU the original problem is still there.
My symptoms of Limp Mode were as it suggests, limited power. I could cruise on the M5 at 70mph, but as soon as I asked for power to over take or go up a hill, nothing! It slowed down to 50mph, even stirring the gearbox gave no more power.
A pain, but it can be driven around, got me home, and that was a round trip of 300 miles with the Limp Mode on....