TL;DR
- What: The pin assignments of the 88-pin engine control module (ECM, “DME”) connector on the E36 M50, for both versions: Bosch DME M3.1 (non-VANOS, 1992) and Bosch DME M3.3.1 (VANOS, 1993–1995).
- Why: When a sensor or actuator misbehaves, checking the signal and the wiring at the ECM connector tells you whether the fault is the part, the wiring or the ECM.
- Important: The two versions use different pins for many functions, injectors and ignition coils included. Use the table for your DME.
Which DME do you have?
| Engine | Engine management (Bentley) |
|---|---|
| M50, 1992 | Bosch DME M3.1 |
| M50 with VANOS, 1993–1995 | Bosch DME M3.3.1 |
| S50US (US M3), 1995 | Bosch DME M3.3.1 |
| M52 and S52US, 1996–1998 | Siemens MS41.1 (OBD2): a different system and connector, not covered here |
Both M50 systems have distributorless ignition: one coil per cylinder, each driven by its own ECM output.
Before you probe the connector
Bentley’s rules, there to protect the ECM:
- Wait at least 40 seconds after switching the ignition off before unplugging the ECM. Residual power in the system relay can damage the module if you unplug it sooner.
- Connect and disconnect the ECM connector and your meter probes with the ignition off.
- Use a breakout box where possible, so you can measure with the ECM connected and without spreading the small terminals. The alternative is to separate the connector housing and measure from the back of the connector.
- Test with a digital multimeter or an LED tester only: an analog meter or a bulb test light can damage the ECM.
- A replacement ECM must be coded for the car (engine, transmission and so on) before it is fitted.
Where it is: the ECM sits in a compartment at the right rear of the engine compartment, by the bulkhead. The cover is held by four captive screws; the connector releases with a fastener and pivots up off the module.
Bentley’s advice on reading the results: no voltage or no continuity usually means a wiring or connector problem. A wrong value doesn’t automatically mean the component is faulty, so check for loose, broken or corroded connections before replacing parts.
Bosch DME M3.1 (M50, 1992)
Vacant pins are left out.
| Pin | Type | Function |
|---|---|---|
| 1 | Output | Fuel pump relay control (needs the crankshaft position signal to switch) |
| 2 | Output | Idle speed control valve, close signal (pulsed ground) |
| 3 | Output | Injector, cylinder 1 |
| 4 | Output | Injector, cylinder 3 |
| 5 | Output | Injector, cylinder 2 |
| 6 | Ground | Ground for the injector output stages |
| 8 | Output | Check Engine lamp |
| 11 | Output | Throttle position (load) signal to the transmission control module |
| 12 | Input | Throttle position sensor signal |
| 13 | Output | Mass air flow sensor hot-wire burn-off (for 0.5 s after shutdown) |
| 14 | Ground | Mass air flow sensor ground |
| 16 | Input | Cylinder identification sensor (AC pulse between pins 16 and 44) |
| 17 | Output | Fuel consumption signal to the instrument cluster |
| 23 | Output | Ignition coil, cylinder 2 |
| 24 | Output | Ignition coil, cylinder 3 |
| 25 | Output | Ignition coil, cylinder 1 |
| 26 | Input | Battery voltage at all times (terminal 30) |
| 27 | Output | Main relay control (to relay terminal 85) |
| 28 | Ground | Ground for the ECM and sensor shielding |
| 29 | Output | Idle speed control valve, open signal (pulsed ground) |
| 31 | Output | Injector, cylinder 5 |
| 32 | Output | Injector, cylinder 6 |
| 33 | Output | Injector, cylinder 4 |
| 34 | Ground | Ground for the output stages |
| 36 | Output | Evaporative purge valve |
| 37 | Output | Oxygen sensor heater relay control |
| 41 | Input | Mass air flow sensor signal |
| 43 | Ground | Ground for the temperature sensors and throttle position sensor |
| 44 | Input | Cylinder identification sensor (pair with pin 16) |
| 48 | Output | A/C compressor control |
| 50 | Output | Ignition coil, cylinder 4 |
| 51 | Output | Ignition coil, cylinder 6 |
| 52 | Output | Ignition coil, cylinder 5 |
| 54 | Input | Battery voltage from the main relay (terminal 87) |
| 55 | Ground | Ground for ignition control |
| 56 | Input | Battery voltage with key on or engine running (terminal 15) |
| 59 | Output | Throttle position sensor supply (5 V) |
| 60 | Input | Programming voltage, from the data link connector |
| 64 | Input | Ignition timing intervention from the A/T control module (during gearshifts) |
| 65 | Input | A/T range switch: park/neutral signal |
| 67 | Input | Crankshaft position / rpm sensor (AC voltage between pins 67 and 68) |
| 68 | Input | Crankshaft position / rpm sensor (pair with pin 67) |
| 70 | Input | Oxygen sensor signal (0–1 V, fluctuating when running) |
| 71 | Ground | Oxygen sensor signal ground |
| 73 | Input | Road speed signal from the instrument cluster |
| 74 | Output | Engine speed (TD) signal to the instrument cluster |
| 77 | Input | Intake air temperature sensor (0–5 V, varies with temperature) |
| 78 | Input | Coolant temperature sensor (0–5 V, varies with temperature) |
| 81 | Input | Drive-away protection enable, from the on-board computer |
| 85 | Input | A/C pressure switch signal, from the climate control module |
| 86 | Input | A/C compressor on request, from the climate control module |
| 87 | Input | Diagnostic RxD, to pin 15 of the data link connector |
| 88 | In/out | Diagnostic TxD, to pin 20 of the data link connector |
Bosch DME M3.3.1 (M50 VANOS, 1993–1995)
Vacant pins are left out. Note how many functions moved compared with M3.1.
| Pin | Type | Function |
|---|---|---|
| 1 | Output | Fuel pump relay control (needs the crankshaft position signal to switch) |
| 2 | Output | Idle speed control valve, close signal (pulsed ground) |
| 3 | Output | Injector, cylinder 5 |
| 4 | Output | Injector, cylinder 6 |
| 5 | Output | Injector, cylinder 4 |
| 6 | Ground | Ground for the injector output stage |
| 7 | Output | VANOS solenoid (camshaft actuator) |
| 8 | Output | Check Engine lamp |
| 11 | Output | Throttle angle signal to the A/T control module |
| 13 | Input | Oxygen sensor signal (0–1 V, fluctuating when running) |
| 14 | Input | Mass air flow sensor |
| 15 | Ground | Ground |
| 16 | Input | Crankshaft position / rpm sensor (AC voltage between pins 16 and 43) |
| 17 | Input | Camshaft position sensor (Hall effect) |
| 23 | Output | Ignition coil, cylinder 4 |
| 24 | Output | Ignition coil, cylinder 6 |
| 25 | Output | Ignition coil, cylinder 5 |
| 26 | Input | Battery voltage at all times (terminal 30) |
| 27 | — | Main relay activation (relay terminal 85) |
| 28 | Ground | Ground for the ECM and sensor shielding |
| 29 | Output | Idle speed control valve, open signal (pulsed ground) |
| 31 | Output | Injector, cylinder 3 |
| 32 | Output | Injector, cylinder 2 |
| 33 | Output | Injector, cylinder 1 |
| 34 | Ground | Ground for the remaining output stages |
| 36 | Output | Evaporative purge valve |
| 38 | Output | Oxygen sensor heater relay control |
| 40 | Ground | Oxygen sensor signal ground |
| 41 | Input | Mass air flow sensor voltage signal |
| 42 | Input | Vehicle speed signal from the instrument cluster |
| 43 | Input | Crankshaft position / rpm sensor (pair with pin 16) |
| 44 | Ground | Ground for the intake air and coolant temperature sensors and the throttle position sensor |
| 45 | Ground | Ignition circuit shield |
| 46 | Output | Fuel consumption signal to the instrument cluster |
| 47 | Output | Engine speed (TD) signal to the instrument cluster |
| 48 | Output | A/C compressor relay control |
| 50 | Output | Ignition coil, cylinder 1 |
| 51 | Output | Ignition coil, cylinder 2 |
| 52 | Output | Ignition coil, cylinder 3 |
| 54 | Input | Battery voltage from the main relay |
| 55 | Ground | Ground for ignition control |
| 56 | Input | Battery voltage with key on or engine running (terminal 15) |
| 57 | Input | Ignition timing intervention from the A/T control module |
| 59 | Output | Throttle position sensor supply (5 V) |
| 60 | Input | Programming voltage, from the data link connector |
| 64 | Input | A/C on signal, from the climate control module |
| 65 | Input | A/C pressure signal, from the climate control module via the pressure switch |
| 66 | Input | Drive-away protection enable (starter immobilization relay) |
| 69 | Input | Knock sensor 2 (cylinders 4, 5, 6) |
| 70 | Input | Knock sensor 1 (cylinders 1, 2, 3) |
| 71 | Ground | Ground for the knock sensors and shields |
| 73 | Input | Throttle position sensor signal |
| 77 | Input | Intake air temperature sensor (0–5 V) |
| 78 | Input | Coolant temperature sensor (0–5 V) |
| 81 | Input | A/T park/neutral position signal |
| 87 | Input | Diagnostic RxD, to pin 15 of the data link connector |
| 88 | In/out | Diagnostic TxD, to pin 20 of the data link connector |
Using the tables
- Injector or coil complaints: find the cylinder in the table for your DME, then test from that pin to the component. The pin for “cylinder 1” differs between M3.1 and M3.3.1.
- Sensor readings: the temperature sensors give 0–5 V that changes with temperature. The oxygen sensor fluctuates between 0 and 1 V with the engine running. The crankshaft sensor produces an AC voltage across its two pins while cranking.
- Power and grounds first: before condemning a sensor, check the ECM’s supplies (terminal 30, terminal 15, main relay feed) and its ground pins with a voltage-drop test. See the ground distribution guide.
- Full circuits: for wire colours and everything between the ECM and each component, use the electrical wiring diagrams. See How to read the E36 ETM.
