Limp home, but no error logged?

[IanCress]

My parents bought a 2008 Mitsubishi Outlander 2.0 Di-D a couple of years ago. Occasionally when being worked hard it will drop in to limp home mode. This usually happens when towing their caravan.
Simply switching off the engine and immediately restarting it brings it back to normal again.

However, the EML never comes on (it does display in the self test at start-up). They have taken it to a couple of garages over the past few years who say there are no errors logged, and of course the car performs fine.

There are quite a few reports of this on the web, but nobody has reported a fix. 'Experts' suggest that since the EML light isn't coming on then it must be a mechanical issue. However the fact that the engine comes back to life immediately when the car is restarted makes me feel it probably is an electronic issue, but for some reason the EML doesn't show.

Incidentally the engine is a 2.0 VW unit, though I don't know how many components are shared.

Anyone know anything about diagnostics on this vehicle? I have a simple OBD reader but it never finds any faults.

[IanCress]

Sorry, I didn't explain properly. The car is still running but at a very reduced power level. On the motorway with the caravan attached it will only achieve 30-40mph.

[IanCress]

That's quite shocking, I didn't even realise that kind of thing could be done.

I don't think that's the case with my parents car, as a number of other people have posted on the web saying they have the same issue.