I would be very grateful if anyone could offer any advice on the following Zafira problem...

I have a 2010 vauxhall zafira 1.9 CDTi diesel with 94,000 on the clock and have owned it for ten years. The car has been very reliable and always starts first time, every time. But about 5 years ago it started going into limp mode once or twice a year where the car starts but has no power or revs and will not go over 5 mph. There are no warning lights showing. When this happens I found that if I switch the engine off, lock the car, then un-lock it the car usually starts and drives ok.

Earlier this year when it happened, I took the car to a vauxhall dealer and they ran some diagnostics on it and said there were no problems with the car and there were not any error messages on the engine-control unit (ECU). They then advised me that once a month, I should drive on the motorway for 20-30 minutes in 4th gear with the revs between 3,000 – 4,000 rpm and that should rectify the problem.

As it is a diesel, I always try to avoid too many short journeys an do try to give the car a good run every few weeks including the motorway runs with revs over 3,000 rpm. As well as doing several steep hill climbs in 3rd gear with revs over 3,000 rpm to help clear the exhaust system.

So I am assuming this is related to the DPF (diesel particle filter) on the exhaust system. What is the best way to force a re-gen of the DPF?

I know other people have posted about the same Zafira limp-mode issue but have not seen anyone post that they really fixed the problem.

Also, would using a diesel additive to clear the DPF help matters?

Thanks in advance for any responses.