Hi Tom,

That generation of Citroen C4 doesn’t have the greatest reliability record, with gearbox and electrical issues being the most oft-reported complaints. Check everything electrical on it works properly, especially the ratio, and that it goes through the gears smoothly. Check for excessive black or, worse, white smoke from the exhaust, during cold start-up and under hard acceleration on a test drive, as they might be indicative of turbo and/or diesel particulate filter problems.