What's up with my Peugeot 307 HDi?

My Peugeot 307 HDi wagon (370,000km on the clock) still runs beautifully but comes up with various faults. Some cause it to derate, others cause the cruise control to not function. Examples include turbo overboost, EGR sensor malfunction, depollution system faulty, air-conditioning refrigerant low, electronic circuit high voltage, etc.

Any word on what could be causing all this?

I am totally lost as to how to stop this occurring.

Jon Wells (Darlington Point)

Aug 2025 Filed under: fault

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Expert answer

Hi Jon,

At that mileage, your car is likely suffering from voltage fluctuations and ageing wiring and connectors, all of which can lead to the issues you are describing. 

I'd suggest you go back to basics and have the battery, alternator and each and every earth connection checked and cleaned for starters. Then plug the car into a diagnostic computer (any good mechanic can do that) and clear the faults before driving it and plugging it in again to see what comes up.

Some common 307 HDi issues we know of:

- Boost control solenoid
- EGR valve or position sensor
- BSI (Built-In Systems Interface) can act up with water ingress or voltage surge

In summary, there's unlikely to be a simple fix to this, but it's almost definitely electrical.

Shane O' Donoghue - Complete Car Advisor