Engine Management Light

My Freelander TD4 auto 54 has got an issue with the EML coming on and going off.
I use the car to tow my horse trailer and recently on a trip out the engine lost power and the EML came on.
After the car was turned off and restarted the next day the EML light went back off.
I assumed I had overtaxed the engine with a long trip towing the trailer, but now the EML comes back on sometimes when towing or stuck in heavy traffic but always goes out when the car is left overnight.
The car shows no other signs of problems and unlike other forum users doesn't loose power or blow smoke.
A local garage has said it need s a new 'boost pump' but can find no mention of this part/problem on the forum.
Am I being fobbed off?
Any thoughts or advice would be gratefully received.

You need to get the fault codes read. As far as I am aware if your car is pre 2004/2005 then you will need the L/R diagnostics if 2005 onwards then most reader/scanners will read and clear engine ECU faults. Diesels did not become OBD2 compliant until 2004/2005.