3wheeldrive

It was probably a loose connection/corrosion. Not a major at all.

The reason a faulty coil pack / connection between coil pack and spark plug can cause errors with ABS etc is because they produce alot of electromagnetic noise (they step 12v up to 10000+v) which can be coupled onto sensitive signal lines used for sensors which causes the ECU to detect abnormal voltages and disables the system (abs etc). It can seem almost random at certain temperatures/ humidities or vibrations while driving. On different vehicles it can cause different errors to show. For instance on a Honda Jazz the ECU would trigger limp mode with a code "Crank position sensor fault" . The wiring loom to the crank position sensor also had the power and trigger wires for the ignition coils. The electrical noise/spikes from the faulty coil pack was coupled onto the signal wire by electromagnetic induction which caused the ECU to flag the sensor as faulty. Something similar can happen if the battery is aging. The internal resistance increases which basically allows electronic noise to increase and affect electronics expecting a stable low impedance DC source.