Mondeo 2009 TDCi engine malfunction but no fault codes

I have a 2009 Mondeo TDCi with 159,000 miles on clock

Intermittently the engine malfunction light and the ESP light come on and the display says Engine Malfunction – the car goes into limp mode.

If I turn the engine off and then back on they disappear and may not come on for a few miles (anywhere between ½ mile and 20 miles. They usually come on when gong up an incline after driving on the flat. Occasionally it is only the engine malfunction light and that does not appear to affect the turbo.

When it is running without warning lights the engine is very smooth and the turbo working

I have also tried pressing the ESP switch when the lights came on but that makes no difference – if I press it with the engine off then the Off light comes on

My garage has looked at it and the only fault showing on their scan was the failure of a glowplug. The glowplugs have all been replaced and this has had made no difference. They also found a vacuum hose that had split which they repaired

Any ideas?