Autopapyrus · Mercedes-Benz M-Class (W164) 3.5 V6 M272 (2007)
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Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.
Mercedes-Benz M-Class (W164) 3.5 V6 M272 (2007): Starter Circuit Wiring and Diagnosis
The W164 starting circuit with the M272 engine is not a simple "key - relay - starter" setup. Starting is handled through the electronic ignition switch, the engine control module, and the transmission selector position signal. Below is the general principle of the circuit and the order in which to check it. Verify exact pin numbers and wire colors against the manufacturer's service information for your VIN.
Part
- 🔩 Determined by the diagnostic results. Typical candidates: starter motor assembly (with solenoid), battery, terminals and ground cables, ignition switch (EIS electronic ignition switch module), circuit 50 relay or control module
Step by step
8 steps- Power circuit (terminal 30). Battery positive runs through the fuse box to a heavy-gauge power cable on starter terminal 30. The ground circuit runs from the battery negative to the body and to the engine block. Voltage drop on the positive and ground cables during cranking should be small, roughly no more than 0.3-0.5 V on each. Battery voltage during cranking should not sag below about 9.5 V.
- Control circuit (terminal 50). This is the thin wire going to the starter solenoid. Voltage is supplied to it only after a command from the electronic ignition switch (EIS) and the engine control module. There is no direct connection from the key to terminal 50, as on older cars.
- Electronic ignition switch (EIS). It verifies the key (smart key or transponder key), enables the "start" position, and sends the request over the CAN bus. If the key is not recognized or the switch is faulty, the starter will not receive a command. In this case the instrument cluster warning lights often do not come on either.
- Engine control module (ME). It receives the start request and sends control voltage to circuit 50 if the conditions are met: valid immobilizer, correct CAN communication, and normal system voltage. Once the engine starts, it cuts the voltage to terminal 50 on its own, without waiting for the key to be released.
- Transmission interlock. Starting is allowed only in selector positions P or N of the 7G-Tronic. The position signal comes from the transmission control module or the selector module over CAN. If the starter is dead in only one position and the engine starts when you shift to N, check the selector position sensor or module and its adjustment.
- Starter solenoid. When voltage is applied to terminal 50, the solenoid pulls in, engages the pinion gear, and closes the main power contacts. A click without cranking points to a problem with power, ground, or the solenoid contacts. Complete silence means there is no command on circuit 50.
- Diagnostic order. First check the battery and terminals (resting voltage, then during a start attempt). Next, read the fault codes in the EIS, ME and transmission modules. Then measure the voltage at starter terminal 50 during a start attempt. If voltage is present but the starter does not crank, the starter itself or the power circuit is faulty. If there is no voltage, look for the cause upstream: the selector, EIS, ME, wiring, and the fuses in the SAM modules (front and rear fuse and relay boxes).
- Starter removal, if diagnosis points to it. Disconnect the battery negative terminal. On the V-type M272, the starter is located in the valley of the engine block, and access is awkward. Part of the intake tract and the under-covers will need to be removed. For the mounting bolt and terminal torque, see the manufacturer's service information, and do not overtighten the power cable terminal nuts.
Common mistakes and warnings
- Before any work on the power circuit, disconnect the battery negative terminal, and keep in mind that this vehicle has additional loads and electronics sensitive to voltage drops. Do not short the starter terminals with a screwdriver while the electronics are powered: this can damage control modules. If you have no experience with CAN bus and electronics, leave the diagnosis to a repair shop.