A faulty engine control unit (ECU) most often shows up as the engine management light coming on with fault codes for several sensors at once, starting problems, the engine cutting out, or limp mode with a loss of power. The same symptoms, however, can come from a faulty sensor, a weak battery or a bad earth. So if you want to know how to check an ECU, start by reading the fault codes with a diagnostic tool, then measure the ECU's power supply and earths. You can only judge the ECU itself once everything around it is in order.

A faulty engine control unit (ECU) can either be repaired or replaced with another working unit that has the same part numbers. Repair, also known as ECU refurbishment or reconditioning, makes sense for minor electronic faults, as long as the circuit board, processor and memory are intact. After water damage, a burnout or a fault that keeps coming back, replacement is usually the only option left. Below we explain what ECU refurbishment involves, what affects ECU repair and replacement costs, how to match an ECU by its numbers and what needs to be done so that the car starts after the replacement.

A faulty ABS module, also called the ABS pump controller, can be repaired or replaced with a used, original control module or a complete ABS pump with the same part numbers. Repair, also known as reconditioning or rebuilding, makes sense for minor electronic faults, such as cracked solder joints, as long as the circuit board and processor are intact. After water damage, a burnout or a fault in the hydraulics, replacement is usually the only option left. Below we explain what ABS module repair involves, what affects the ABS pump repair cost and the ABS pump replacement cost, how to match a part by its numbers and what needs to be done after fitting.

A faulty gearbox control unit (TCU), also known as the gearbox controller or gearbox ECU, can be repaired or replaced with a used, original control unit or mechatronic unit that has the same part numbers. Repair, also called reconditioning, makes sense for minor electronic faults, such as cracked solder joints, as long as the processor and memory are intact. After water damage, a burnout or a fault that keeps coming back, replacement is usually the only option left. Below we explain what gearbox control unit reconditioning involves, what affects the gearbox ECU repair cost and the cost of replacement, how to match a used control unit by its numbers and what needs to be done after fitting.

The best-value way to get an original comfort controller is to buy a used one from another car with the same part number as yours. We explain how to tell whether the comfort control module is really at fault, how to match a replacement and what to do after fitting.