VW / Audi / Seat / Skoda (VAG) Bosch EDC16U34 Engine ECU Repairs

Type: Bosch
Fits: VAG – Audi / Seat / Skoda / Volkswagen (VW)
Fuel: Diesel
Ref: ECUT335295

Note: This ECU may also fit other models.

Almost every fault on a modern diesel is settled by asking the engine ECU what it has seen. The EDC16U34 has a commonly reported failure that takes the question away: the engine will not start, and a diagnostic tool gets no reply from the unit at all. No codes, no live data, no part named. It is a diesel engine ECU, and units of this type are tested and rebuilt on our own benches.

A fault that leaves nothing to read

The car cranks and does not fire. The tool either finds nothing where the engine ECU should be or reports that it cannot establish communication, and that is the whole of the evidence.

Silence is not a milder version of a fault code. A code points somewhere, and even a misleading one narrows the search to a circuit and a component. A fault that leaves nothing behind points everywhere at once, and on a car that will not start, everything electrical becomes a candidate.

How this ends up read as a key or wiring problem

From the driver’s seat, a no-start with nothing to read looks like an immobiliser or key problem. From the diagnostic socket, it looks like a broken wire, a dead bus or a gateway that has stopped passing messages on. So keys get suspected, looms get chased, and other modules get drawn into a fault none of them caused.

None of that is careless; it is the reasonable reading of the only evidence there is. What makes it go wrong is structural: the one part of the car that cannot be interrogated is the part that has failed. Everything else can be tested and cleared on the vehicle. This unit cannot answer for itself, so it survives every round of elimination.

What has to be cleared before the unit is the suspect

A module that is not being fed cannot answer, and one that cannot answer is not necessarily faulty. Three checks come before the ECU is suspected at all.

• Power and earth at the unit’s own connector, and the fuses on those feeds. A unit with nothing coming into it has nothing to reply with.
• The engine-control power-supply relay in the fuse panel, which is what puts those feeds live in the first place.
• Whether anything else on the car answers. If every module is silent, the fault is the diagnostic connection, the bus or the gateway rather than this ECU. If everything else replies and only the engine ECU does not, the suspicion has narrowed properly.

Only once those are clear does the unit itself become the suspect. A unit that has stopped answering has usually failed in one of a small number of ordinary ways, none of them peculiar to this model — the same ways any engine ECU stops working, which we set out in our guide to what actually fails inside an engine ECU.

The opposite case, when the unit names itself

Not every failure here is silent, and the other one worth knowing is its mirror image. P0606 is reported on this unit as an internal processor fault in the engine control module — a code that names the ECU rather than something attached to it. Nearly every other code describes what the unit saw elsewhere. A code that names the box is not one to chase around the engine bay, and it belongs in the notes when a unit is sent to us.

Testing a unit that will not talk on the car

Once the feed checks are clear and the unit is still not answering, diagnostics on the vehicle has run out of instrument. There is nothing further to read. What remains is to take the unit somewhere it can be powered up on its own terms and asked directly.

That is what a bench is for. The unit is given power and earth from a bench source rather than from the vehicle, put on a bus of its own, and watched to see whether it comes up at all. On most faults that is one step among several. Here it is not a last resort; it is the only measurement left.

What we do with a unit is repair it. Remapping, cloning and immobiliser removal are not services we offer.

The VAG diesels this unit came from

The EDC16U34 is a mid-2000s VAG controller, fitted to the PD generation of 1.9 and 2.0 TDI engines — the Golf V, Caddy, Touran, Jetta, Bora and Eos, the Audi A3, the Octavia, and the Seat Leon, Altea and Toledo. The badge makes no difference to what is inside, and Seat sits as a marque of its own here, with the rest of its engine ECUs beside it.

What the workshop does with a unit that will not answer

A unit that arrives is booked in under a reference of its own, inspected, then put on power and tested electrically — on this fault, the first time anything has been able to ask it a question. What the test finds goes to you first, with what putting it right involves, and no chargeable work starts before you have agreed to it. Our engineers work at component level on the board that came out of your vehicle, in our own UK workshop, and nothing goes back until it answers properly on the bench a second time. The repair we carry out is warranted for 24 months.

The detail that helps most is what the tool actually did: nothing from any module on the car, or everything answering except the engine ECU. Those two point in different directions, and writing that down on the Repair Form sets up the bench test before the box is unpacked. The vehicle stays where it is; only the unit travels, from anywhere in the UK.

Common part numbers associated with this type of unit