Bosch DME M 3.1 Engine ECU Repairs

Type: Bosch Engine Management
Fits: BMW 320i / 325i / 330i / 520i / 535i / 635i / 735i
Engines: E32 / E34 / E36
Year: 1985 – 1992
Ref: ECUT313195

Note: This ECU may also fit other models.

Draw a grid with the four BMW badges that run a Bosch DME M3.1 down one side and its two Bosch numbers across the top, and every square fills in. The E34 520i and 525i and the E36 320i and 325i have each been recorded with 0 261 200 402 and with 0 261 200 403. The car will confirm you are on the right page, but it will not tell you which of the two units you are holding.

Four badges, two chassis, eight filled squares

Neither reference is confined to one chassis. Neither is tied to the smaller or the larger engine size. In the listings we checked, 0 261 200 402 and 0 261 200 403 each turn up in both the E34 and the E36, and against all four badges.

On some DME pages the badge on the boot lid points to a single row before the unit has left the car. Here it points to both, so we do not assign either reference to a particular model, and we would ask you not to either.

The first check: a non-VANOS M50

What the car does settle is the family. The M3.1 is the engine management for BMW’s M50 straight-six in its earlier, non-VANOS form, and that is the engine both references on this page are documented on.

So an E34 520i or 525i, or an E36 320i or 325i, with that engine belongs here. If the case on your DME names something other than M3.1, trust the case over the car and look through our BMW Motronic pages for the designation it gives.

Passing this check tells you the page is right. It leaves the choice between 402 and 403 exactly where it was, because both run the same six-cylinder in the same four cars.

Two Bosch numbers for one engine: reading the label

On paper the two references look like duplicate entries for one job: same engine, same models, same chassis. They are still separate Bosch part numbers, and we identify a DME by what is printed on its case, not by the car it came out of.

The label carries two numbers: Bosch’s, which on both units here begins 0 261 200, and BMW’s own. For 0 261 200 402, the BMW number documented beside it is 1748401, a pairing that repeats across the listings we checked.

Whichever unit you have, quote both numbers exactly as they appear on the case, digit for digit, even where they differ from what you expected to find. If part of the label has worn away, send what is legible and tell us which part is missing; a partial label is more use to us than a number worked out from the model.

What happens to your M3.1 in our workshop

The DME is booked in and examined by eye, then given electrical tests and diagnostics chosen for the fault you reported. It stays with our own engineers in our own UK workshop, worked on with our own equipment, and is never passed to anyone else.

Once the cause is known, we tell you what we found and quote for the repair. No chargeable work starts until you have given the go-ahead.

The repair itself is at component level. Failed parts on the circuit board are traced and reworked under a microscope with temperature-controlled equipment, and the unit is released only after it passes final testing. The specific repair we carried out is then covered by our 24-month warranty.

Because it is your own DME that we repair, the Bosch and BMW numbers on its case are the ones that come back to you.

Sending the unit in from anywhere in the UK

We work as a mail-in workshop and take units from across the UK. Before the DME is packed, open the Repair Form and give us both label numbers, the model and chassis, and a line or two on how the car has been running.

If the engine ECU came from a car of another make, every other badge we repair is listed from our main engine ECU page.

Both Bosch references are set out below, so the number on your case can be checked against them before anything goes in the post.

Common part numbers associated with this type of unit