Étage de sortie du calculateur hors service

The transistor stage inside a control module that switches an actuator has failed. It is the least common explanation for most circuit codes and should be the last conclusion, not the first — the wiring and the actuator are both far more likely and both far cheaper.

But the reason it matters is what usually kills it. These drivers switch inductive loads — injectors, solenoids, relays, heaters — and every switch dumps the collapsing magnetic field back into the driver. They run hot and stressed by design. When one fails, the common cause is a short in the load it was driving: a shorted injector, a glow plug that has failed short, a solenoid with a broken-down winding.

Which is the practical point: measure the actuator before replacing the module. A new module fitted into the same short destroys its driver too, and that is an expensive way to learn what the meter would have shown in a minute.

Failures are usually one output at a time rather than the whole module, so the pattern is faults on one or two circuits while everything else works normally. Expect a replacement module to need programming and coding, and on some vehicles to hold calibration data that must be transferred with it.