THE AA has warned motorists in the Thames Valley and South East not to pressure wash their way to a breakdown when cleaning the car.

Many people have invested in high pressure washers, widely available at DIY stores for domestic use. But they may be unaware that using these washers on their car can lead to a breakdown and an expensive repair bill.

Tim Shallcross, head of Technical Policy for AA Roadside Services, said: "AA patrols in the region are coming across more and more cases where motorists have used high pressure washers to get the engine looking clean and shiny. However, the washers can force water into parts of the car and engine where it shouldn't be.

"The electrical connectors under the bonnet are highly protected by the manufacturer, but they are not designed to withstand being blasted by high pressure washers."

Typical faults which can develop include the car simply not starting, warning lights appearing on the dashboard, windscreen wipers operating when not expected to, or the lights not coming on.

The danger of using high pressure washers to wash the car does not stop at using them to clean the engine, they can also cause problems when cleaning the outside of the car. The high pressure can force water through seals into the boot or interior. AA patrols have found water in CD multi-changers which can cause warning signs to be displayed on the dashboard.

Today's cars are much more complex than 20 years ago when they simply had one computer to run them. Modern vehicles tend to have 40 or more computers, meaning there are more possibilities for complex problems. High pressure power washers can force water into fuse boxes, relay boxes and connectors which can be found all over modern cars, and can cost hundreds of pounds to repair.

Mr Shallcross added: "A bit of grime on the engine does the car no harm. It is safer to leave it there than to risk short circuiting expensive electronic components."