VW / Audi / Seat / Skoda (VAG) Bosch M3.8.4 Engine ECU Repairs

Type: Bosch Engine Management
Fits: VAG – Audi / Seat / Skoda / Volkswagen (VW)
Fuel: Petrol
Ref: ECUT186195

Note: This ECU may also fit other models.

A VAG engine ECU can be filed under more than one vehicle-manufacturer number, and on this designation the second form is easy to miss. All three references we hold for the Bosch M3.8.4 read 8D0 907 558 with a letter after them. Units that have already been exchanged once turn up in the published records under 8D0 997 558 instead, different digits in the middle, and an X after the letter.

So a number read straight off a label does not always match what a catalogue prints, and a search for 8D0 997 558 KX can return nothing at all. It is still an M3.8.4, and we still repair it. What follows sets out both number forms, what the three references are documented against, and what to quote when you send a unit in.

The same unit, filed under two vehicle-manufacturer numbers

Two of the three references on this page are recorded with a second VAG number beside the 907 one, and in both cases the record is explicit.

A UK seller’s listing for 8D0 907 558 S puts it in plain words: the part number is 8D0 907 558 S, superseded by 8D0 997 558 JX. That same listing describes the car it came out of as a Volkswagen Passat 1.8 with an ADR engine, 1999 only.

A catalogue record for 8D0 907 558 T carries 8D0 997 558 KX and 8D0 997 558 KV among its OE reference numbers, printed alongside 8D0 907 558 T and the Bosch number 0261204957 rather than in place of them.

The pattern is not confined to these two. A UK trade catalogue covering neighbouring Motronic units on the same platform sets every row out the same way — the Bosch number, then one or two 907 references, then a single 997 number ending in X. Those rows belong to other designations, but the convention holds through the whole table.

What the 997 group means inside VAG’s own parts system is not something these records state, and it is not worth guessing at. The narrower reading is the useful one: the same control unit is filed under more than one vehicle-manufacturer number, and the 997 form is the one that appears on units the records show as already exchanged.

If the number on your unit reads 8D0 997 558

Search 8D0 997 558 JX against a page listing 8D0 907 558 S and nothing matches. The conclusion that follows — wrong page, wrong workshop, unit not covered — is the wrong one, and it is worth saying so plainly.

We repair the M3.8.4 whichever of the two forms is printed on the label. The ten-digit Bosch number on the case identifies the reference at our end, so where the VAG number reads 8D0 997 we take it as it comes rather than asking you to work out which 907 number it answers to.

Three references, one engine application

G, S and T are not three different cars. Every record to hand that names a vehicle against any of the three names the same thing: the 1.8-litre 20-valve petrol engine, in the B5-generation Audi A4 and Volkswagen Passat.

0261204773 / 8D0 907 558 G has the fullest record: a specialist listing gives the car it came out of as a Volkswagen Passat 1.8i 20V, 125 CV, engine code ADR. UK marketplace listings for the same pair name the Passat as well, and one continental listing files the Bosch number under the Audi A4 (8D2, B5).

0261204956 / 8D0 907 558 S is recorded against the Volkswagen Passat B5 1.8, with sellers dating the units they hold anywhere between 1997 and 2000. The UK listing quoted above narrows its own stock further, to a Passat 1.8 with an ADR engine number, 1999 only.

0261204957 / 8D0 907 558 T is recorded against the Audi A4 B5 (8D2), on listings dated 1998 and 1999 and including the Avant, while a UK specialist’s product page pairs it with the Passat as well as the A4. One title in circulation describes the same reference as a 1.8 turbo carrying the engine code ADR, and those two halves do not agree: ADR appears elsewhere in the same records against a naturally aspirated 1.8 20-valve.

Read together, that is one engine application across two closely related cars, with the trailing letter marking a revision rather than a different vehicle. A year on a listing describes the unit that seller had, not a fitment rule. The A4 B5 accounts for most of what arrives against this designation and is one line among many in what else we repair for Audi, while the Passat sits on the Volkswagen side, covered by our Volkswagen engine ECU repair overview.

What happens to the unit here

The work is done in our own UK workshop by our own engineers, on our own equipment, and nothing is sent out. A unit that arrives is logged, visually inspected and electrically tested first, then taken through fault-specific checks on the board itself. Component-level work is carried out under a microscope with temperature-controlled rework equipment, and the job is not finished until the unit has passed final testing.

The unit you send is the unit that comes back, repaired at board level rather than substituted. Nothing chargeable begins until it has been tested, the fault identified and the outcome put to you, and the repair carried out is covered by a 24-month warranty.

What to send and what to quote

Start with the ten-digit Bosch number from the case. Then give the VAG number exactly as it reads on the label, including if it begins 8D0 997 rather than 8D0 907. The car and the engine code are useful as a cross-check, not as the identifier. Those are the details to start a repair enquiry on the Repair Form with, and a photograph of the label covers most of them in one go.

A number that does not appear in the table below is not a verdict on the unit. It gets checked against the board rather than dismissed on the paperwork, because the board settles which reference it actually is.

The three references we hold against this designation are listed below, the Bosch number first and the 8D0 907 558 form beside it.

Common part numbers associated with this type of unit