I have a 2002 Renault Scenic 1.9 DCI with 70k

The electronic fault warning light (also heater plug on light) intermitently comes on with no apparent problem.

It always seems to come on when driving up an incline then goes off after the top is reached or it comes on when you throttle then goes off when you release the throttle. I have checked the turbo hoses, they're all secure.

I then went to the garage and paid £40, they printed out the following;

Connect to sun scanner and read ecu memory for faults, intermittent fault stored with egr valve flow p 1826, cleared fault from system and reset, no fault present on road test, customer to monitor, if fault returns a new egr valve will be required.

The electronic fault warning light still comes on when you throttle, then off when foot is off throttle.

What is a egr valve and how much is it approx? Where is it situated, i.e. is it in a tricky place?

The garage estimated £500, but this includes changing front brake pads