"If not how does the buyer is sure that the car is error free before spending lots of money?" If spending lots of money the best course of action for peace of mind is to only buy from a reputable dealer where you will have some recourse if faults do materialise.

Edited by pkqpr on 24/12/2014 at 18:02

If the seller tries to just clear error codes to sell a defective car, Then the error codes should come back when the vehicle is driven.

Some cars won't light the MIL when even there is an error, It all depends on the car in question and what the codes are. Some Fords don't bring the MIL on even if there are fault codes stored in memory.

If a person has a decent scan tool (not the usual dross sold on auction sites) then it should be able to read any stored codes or any fresh codes brought about by the test driving of a car with a fault.

Anyone?

Some cars built within the last 5 years or so ,have the ability to store code history even if the malfunction light has been extinguished.None of the generic code readers have this facility,so you are going to need to spend around £2k + on equipt to check this.(that is per make)

I've caught a couple of home traders out in the past by hooking up my specific marque diagnostic gear (Lexia & Peugeot Planet).

On Peugeots it records the fault and the mileage it occurred, so even if the codes have been cleared and the car not driven (much) to make the fault light come on, the codes are there.

But, as has been said, cheapo generic readers won't be able to pick up these faults.

It can also light up all the lights on the dash, so its useful to see if any displays or bulbs have been deliberately covered or broken (now that bulbs are integrated into the dash circuit board some traders have been known to stick black electrical tape over them).