Welcome to the most comprehensive guide to diagnosing and repairing the BMW DME/Bosch Motronic M1.2 electronic control unit (ECU). This system is one of the key components in BMW's history, controlling the legendary M20B25 six-cylinder engines at the dawn of the digital era.
On this page, you'll find all the information you need for proper diagnostics and connections: a complete pinout table, terminal diagrams, and a list of models where this system was used.
DME/Motronic M1.2 Applications: Engines and Vehicles
Engine: M20B25 (2.5-liter, 6-cylinder)
Main Models:
- BMW 3-Series E30: 325i, 325is (late 1980s)
- BMW 5-Series E34: 525i (early versions)
- BMW 7-Series E32: 735i, 735iL, 750iL
The Motronic 1.2 system was also used on the high-performance S38B36 engine (M5 E34), although the DME for the M20B25 is technically slightly different.
BMW DME Bosch M1.2 Pinout (S38 Engine)
BMW DME Bosch M1.2 Pinout (E32)
1990 BMW 735i, 735iL, 750iL E32
Complete Pinout Table for the BMW DME M1.2
X6000
| Pin | Type | Description/Function | Connection | Type of Signal | Tester Display | Measurement Notes |
| 1 | A | Ignition terminal | Ignition coil | Primary signal | Oscilloscope | Engine test, test step 05 |
| 2 | M | Ground | Ground point | Ground | ||
| 3 | A | EKP relay and TR signal (crankshaft reference) | EKP relay and electronic transmission control unit |
Ground with superim posed signal |
ON | Can only be measured when crankshaft rotating |
| 4 | A | Idle speed actuator | Idle speed actuator | Pulsed ground | Component activation | |
| 5 | A | Evaporative valve | Evaporative valve | Pulsed ground |
CLOSED/ OPEN |
Perform component activation, ground => closed |
| 6 | A | Engine speed signal | Instrument cluster | Square wave signal | One signal per ignition | |
| 7 | E | Air flow meter signal | Air mass meter | 0...5 V | Load signal ms | See status monitoring |
| 8 | E | Cylinder identification sensor (ignition) | Cylinder identification sensor (connection B) | ON/OFF | See status monitoring | |
| 9 | Not used | |||||
| 10 | M | Ground, oxygen sensor | Oxygen sensor | Ground | ||
| 11 | Not used | |||||
| 12 | Not used | |||||
| 13 | E | RxD diagnostic data line | Diagnostic socket | > 10V | When cover of diagnostic connector closed |
| Pin | Type | Description/Function | Connection | Type of Signal | Tester Display | Measurement Notes |
| 14 | M | Ground, injection valves | Ground point | Ground | ||
| 15 | A | indicator "Check engine" | Instrument cluster | Ground | Comes on if emission related error code is stored, and comes on during starting | |
| 16 | A | Injection valves cyl. (1 + 3 + 5) | Injection valve | Pulsed ground | Injection time ti | Ground $\implies$ Injector valves open, see component activation |
| 17 | A | Injection valves cyl. (2 + 4 + 6) | Injection valve | Pulsed ground | Injection time ti | Ground $\implies$ Injector valves open, see component activation |
| 18 | E | Hot at all times | Terminal 30 | > 10 V | ||
| 19 | M | Ground for electronics and sensor shields | Ground point | Ground | ||
| 20 | Not used | |||||
| 21 | Not used | |||||
| 22 | A | Idle speed actuator | Idle speed actuator | Pulsed ground | See component activation | |
| 23 | A | Air pump relay signal | Air pump relay | Ground | Ground $\implies$ Air pump on | |
| 24 | M | Ground remaining output stages (except for ignition and injection valves) | Ground point | Ground | ||
| 25 | A | Preheating | Air mass meter |
Voltage plus for sim 0,5 second |
Signal stops 4 seconds after engine stops | |
| 26 | M | Ground air flow meter | Air mass meter | Ground | ||
| 27 | E | Ignition terminal 15 | Ignition switch | > 10 V |
| Pin | Type | Description/Function | Connection | Type of Signal | Tester Display | Measurement Notes |
| 28 | E | Oxygen sensor signal | Oxygen sensor | Pulsating voltage up to approx. 1 V | Voltage value | Can only be measured with the engine running at operating temperature |
| 29 | E | Vehicle speed sensor | Instrument cluster | Square wave signal | km/h | |
| 30 | Not used | |||||
| 31 | E | Cylinder identification sensor (ignition) | Cylinder identification sensor (connection A) | ON/OFF | See status monitoring | |
| 32 | A | Measuring signal (KVA signal) | Instrument cluster | Square wave signal | Multimeter function pulse | Oscilloscope |
| 33 | Not used | |||||
| 34 | Not used | |||||
| 35 | Not used | |||||
| 36 | A | DME main relay | DME main relay terminal 85 | Ground | ON | Diagnosis not possible if not fitted, connect jumper at relay terminal 30 and 87 |
| 37 | E | U-Batt from DME main relay | Main relay terminal 87 | U-Batt | Voltage value | Perform status monitoring. Diagnosis not possible if signal not applied. Connect jumper terminal 30 and 87 on relay |
| 38 | E | Drive away protection | On-board computer | > 10 V | ||
| 39 | E | Programming voltage | Diagnostic connector | Only activated for control unit programming | ||
| 40 | A | A/C compressor signal | Pressure switch, compressor relay | ON/OFF | ||
| 41 | E | Auxiliary fan signal | Full load cutoff relay | 12 V | ON/OFF |
| Pin | Type | Description/Function | Connection | Type of Signal | Tester Display | Measurement Notes |
| 42 | Not used | |||||
| 43 | E | Idle CO potentiometer | Air mass meter | 0...5 V | Voltage value | |
| 44 | E | Intake air temperature | Intake air temperature sensor | 0...5 V | ^C | Temperature dependent |
| 45 | E | Coolant temperature | Coolant temperature sensor | 0...5 V | ^C | Temperature dependent |
| 46 | Not used | |||||
| 47 | E | Inductive pulse generator (connection A) | Pulse generator, engine speed/crankshaft position | A/C voltage | Engine speed | Between Pins 47 and 48 (can only be measured with crankshaft rotation) |
| 48 | E | Inductive pulse generator (connection B) | Pulse generator, engine speed/crankshaft position | A/C voltage | Engine speed | Status monitoring at or above starting rpm |
| 49 | Not used | |||||
| 50 | Not used | |||||
| 51 | Not used | |||||
| 52 | E | Idle signal | Throttle switch | Ground | ON | See status monitoring on set idle speed |
| 53 | E | Full load signal VL | Throttle switch | Ground | ON | At full load (kick-down) |
| 54 | E | Coding signal | Fuel coding connector | Ground | ||
| 55 | E/A | TxD diagnostic data line | Diagnostic socket | Ground | When cover of diagnostic connector closed |