Limp Mode Explained

Limp Mode is used to describe when a petrol or diesel, car, van or light commercial vehicle has had its power restricted, has reduced power or restricted engine performance. The ECU controls limp home mode or limp and uses it to help prevent any possible engine or automatic gearbox damage.

When in “Limp” a vehicle is still normally kept driveable and the amount of power available is set by the manufacturer. On turbocharged vehicles “Boost” is often greatly reduced and the engines revs limited to somewhere around 3000 RPM. Automatic transmission equipped vehicles sometimes have their gearboxes locked in a high gear to restrict acceleration.

Limp mode sometimes occurs prematurely or too soon when even only a slight fault is present and detected by the ECU. The Technician can use the OBD X BOX in such circumstances or situations to safely and temporarily override, delete, switch off or remove this OBD limp or limp mode feature. Technicians must use their skill, judgement and experience to decide when it’s safe to over ride limp, based on every different fault or eventuality, limp removal is temporary and only works whilst the module is connected to the vehicle. The OBD X BOX could also help the AA, RAC and Green flag to reduce their recovery costs in roadside breakdown situations.

Some manufacturers, for example VAG, Audi, BMW, VW, MG, Honda, Jeep, Kia, Land Rover, Mazda, Vauxhall, Mini, Nissan, Toyota, Porsche, Mercedes, Renault, Subaru and Volvo refer to it as Limp. Ford call it LOS, meaning Limited Operating Strategy when describing limp mode on their Ford Transit or Connect or Ranger or Focus or Mondeo or Escort or Galaxy, C Max or even Fiesta.

Limp Mode, Limp or LOS is what the vehicles ECU uses to limit or restrict engine power even on auto vehicles or cars with automatic transmission.

Common causes of limp mode, limp home mode, limp or LOS include restricted or blocked DPF’s or diesel particulate filters, faulty EGR valves or faulty and sticking turbochargers.

Another well known cause of limp mode or LOS is when a vehicle fitted with, and using Ad Blue, runs out of Ad Blue fluid or has a faulty injector or NOX sensor. The AA, RAC and Green Flag are often called out to cars, vans and light commercial vehicles with Adblue faults.

When carrying out diagnostic tests to vehicles that are stuck in limp mode, and prior to repairs, the OBD X BOX can prove to be very useful. Sometimes the OBD error code that’s been registered can prove to be a red herring and very misleading, using the OBD X BOX to further drive the vehicle out of limp may bring on other more important and relevant codes.

On some occasions Technicians may need to permanently delete or remove selected fault codes and ECU functions, in these circumstances an ECU remap should be used instead. Remapping companies specialising in Tri Core, OBD, TSM, edge and boot mode remaps and DPF, EGR, Ad blue and fault code deletions or removals include the following specialists. Quantum Tuning, Revo, Superchips, Evolution Chips, Celtic Tuning, Rhino Maps, Darkside Developments and Porsche expert Wayne Schofield of Chip Wizards UK.

The OBD X BOX does not offer a permanent fault code delete solution, when the module is unplugged, the vehicle returns back to being completely standard and not modified.

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