P0351 - coil circuit malfunction - Citroen C5 II

[jendreq]

Hello,

Yesterday while driving the check engine light came on, the Depollution Faulty error was displayed, the car lost power and was working on two cylinders. The computer showed error P0351 - Ignition coil A, primary/secondary circuit malfunction. This is the only error the computer displays (apart from P0597 Thermostat error, but it was always there).
The coil was replaced 4-5 years ago, spark plugs are new. This year I had problems with the BSM and fuel pump relay - I replaced the relay. I suspect that the BSM is causing the problems again, but in such a situation I would expect more errors, it is intriguing.
Today, when the engine has cooled down, it runs normally. Does anyone know how to better diagnose the problem?

The car is Citroen C5 II 2.0 Pb 2005 (no gas installation, pure gasoline).
VIN: VF7**************[VIN obfuscated, can be read by forum staff]

[xantia_v6]

I would be replacing the coil pack again before chasing anything more complicated.

[wheeler]

Today, when the engine has cooled down, it runs normally. Does anyone know how to better diagnose the problem?

Classic behaviour of a failing coil pack.