VW / Audi / Seat / Skoda (VAG) Bosch EDC 1.3.1 Engine ECU Repairs

Type: Bosch
Fits: VAG – Audi / Seat / Skoda / Volkswagen (VW)
Fuel: Diesel
Ref: ECUT220195

Note: This ECU may also fit other models.

A car that runs properly from cold and grows worse as everything under the bonnet comes up to temperature is describing its own fault. Leave it standing long enough to cool and it behaves again. Good cold, poor hot, recovered after a rest: on VAG diesels of this generation that pattern is a documented engine ECU failure mode, and it repeats reliably enough to be worth acting on.

The mechanism is heat inside the box rather than wear on the road. These units suffer internal heat-dissipation problems, so the fault arrives with engine-bay temperature rather than with mileage, and it can come and go with no fault codes at all.

The recovery is as much a part of the picture as the fault: a car that is right again the next morning, and wrong again half an hour into the same journey, is repeating a temperature cycle rather than deteriorating. By the time it is standing in a workshop with the bonnet up and everything cooling, the conditions that produced the fault have gone.

There is a simple way to see whether the pattern holds. With the unit still connected to the loom, position it where a flow of cool air can pass over it, then use the car as you normally would. If the symptoms ease while it is being kept cool, temperature is involved and the ECU has earned a proper test. It is not a repair and it will not hold — it is a way of pointing the diagnosis at the right component before anything is taken off the car.

Two faults on these engines look bad enough to suspect the ECU and usually are not the ECU. Drastic power loss that is consistent — the same from cold as it is hot, on every journey — points first at the injection pump or the air-flow meter. On the 2.5 TDI in particular, an engine that cuts out and will not restart is commonly an injection pump failure, an internal seal rather than anything electronic. Both are worth settling before a unit comes off the car.

The distinction to hold onto is the shape of the fault in time. One that tracks temperature is present at some moments and absent at others, and it moves with how hot the car is rather than with how far it has travelled. A power loss that is consistent — there every time, in the same way, hot or cold — behaves like a mechanical part that has failed, and it belongs with the pump or the metering side before it belongs with us. A unit sent in on the strength of a consistent power loss usually goes home working, with the car still unfixed.

These EDC 1.3.1 units are diesel engine ECUs for VAG five-cylinder 2.5 TDI cars of the early-to-mid 1990s, pre-PD engines, with the Audi 100 and the Audi A6 the confirmed applications. Alongside the temperature-tracking intermittent, the other pattern that turns up at this level is a unit that has lost control of an output: it stops driving something it is meant to drive.

Every unit is booked in, inspected and put on test before anyone forms a view about it. What the testing found, and what the repair would involve, comes back to you with the price on application; no chargeable work starts until you have authorised it. The repair itself is done at component level on your own board, by our own engineers in our own UK workshop, so the unit that goes back into the car is the one that came out. Nothing is signed off until it has passed final testing, and the repair carries our 24-month warranty.

Units from the rest of the Audi range are grouped in our Audi engine ECU index. Everything reaches us by post, from anywhere in the UK.

If a car is good cold and poor hot, that pattern is worth writing down before anything comes off it. Tell us what it does and when it does it on the Repair Form.

Common part numbers associated with this type of unit