Replacing ECU (2000 Megane)

Sam the Sham

We've got a low mileage (77,000 miles) 2000 Renault Megane that is running fine and just passed the NCT... except that at random intervals, sometimes as long as weeks, it just completely stalls out.

The mechanic we took it to was finally able to get it to exhibit the behaviour and said:

1) when it happens, there is no spark to any cylinder.
2) they can't get any reading from the ECU

He concludes that the ECU is shot and tells me it's an expensive job because a used ECU would have to be coded to the immobiliser and non-Renault mechanics can't do that and Renault mechanics will only do it with a new (expensive) ECU. As the car is worth very little, he recommends scrapping it.

My questions:

1) does this sound plausible as a diagnosis?
2) if it is the ECU, is there any cheap way of replacing it?

Guy:Incognito

Haven't done it on a Megane but I've done it on a more complicated c8. It may well be a case of needing to swap other bits with it like getting the keys and immobiliser bits together with the ecu all from a donor car.

If it does come to scrapping it, ill buy it off you for a couple of quid over scrap price. I quite like those meganes and wouldn't mind a project while I'm not working

CiniO

I remember once when ECU dies in my Cinquecento, I was able to get uncoded ECU.
After plugging in, and starting the engine for the first time it read code from key, and coded immobileiser to that key automatically, so after that only my key could start the engine.

I'm not sure though if it's possible to get ecu like that for megane.

BrianD3

Be careful before accepting that diagnosis and replacing the ECU. Running and starting problems on that model would most commonly be caused by
-Plug coils
-Crank position sensor and its wires

Does the car stop while running? Does it run badly and then stop or just stop suddenly? What happens then, is it hard to restart?

If it is indeed the ECU, this crowd claim to be able to diagnose problems and repair them
http://www.autokey.ie/

Sam the Sham

Thanks for the replies.

To answer your questions, BrianD3:

The car does stop while running. I wouldn't say it "runs badly" before stopping. It just loses all power abruptly. And then, yes, it is hard to restart. Does that tell you anything?

The mechanic didn't think it was the plug coils because it would be unusual for all 4 to go out at once. He did suggest that it might be the crank position sensor but because he couldn't get a code reading from the ECU he couldn't know for sure that it was that. Given the age of the car, I didn't think it worth spending the €200 he quoted on what would really be a stab in the dark.

shamwari

To me, no comms like this suggests a power supply problem to the ECU. It could be wiring, fusebox, ignition switch or a main relay. The latter once caused a similar problem in an Astra belonging to me !

Personally I'd look for a second opinion before condemning the ECU

gctest50

Long vaguely related shot :

Peugeot after deep thought about how to make money on repairs put a block connector in the drivers footwell at the lowest point under the carpet, it corrodes and causes all sorts you wouldn't expect
- continues running after turning off and removing the ignition key, leaves 2 or 3 warning lights on the dash, the switches for A/C etc are "kind of " active, immobilised now and again

source : fixed one b4

.

Stella Virgo

try replacing the ignition/engine relay switch......after all it is a 14 year old car.....bout a fiver to buy.

Sam the Sham

Just to follow up on this: it wasn't the crank positioning sensor. We plugged a new one in and the engine still cut out. At that point, we were going to scrap the car, but we couldn't find anyone to give us more than €100 for it. The car only has 77,000 miles on it and comparable cars sell for €1,200 and up. So as a financial proposition, it made no sense to scrap it. We had it towed to autokey.ie (thanks for the recommendation, BrianD3!) and, sure enough, it was the ECU. It cost €430 to fix. Now we're planning to sell it at auction, mostly because we don't have the energy or the time to sell it ourselves. Still a better financial proposition than scrapping it would've been.