Power Supply
When testing power supply to an ECM, the DIS/MoDIC multimeter function as well as a reputable hand held multimeter can be used.
It is best to make the checks at the ECM connection, this method includes testing the wiring harness.
The correct Universal Adapter for the MS41.X application should be used (#88 88 6 614 410). This will ensure the pin connectors and the harness will not be damaged.
Identifying Universal Adapter. Scheme 326
The interior of this Universal Adapter is shielded, therefore it is vital that the ground cable is connected to the vehicle chassis whenever the adapter is used.
The adapter uses a Printed Circuit board inside keeping the capacitive and inductive load to a minimum.
When installing the Universal Adapter to the ECM (E36 located below the windshield on the passenger side of the engine compartment, Z3/E39 in the Electronics Box), make sure the ignition is switched off.
The Engine Control Module Relay should be tested using the relay test kit (P/N 88 88 6 613 010).
This kit allows testing of relays from a remote position.
Always consult the ETM for proper relay connections.
Identifying Air Management System. Scheme 327
Throttle Valve: The mechanical throttle valve regulates the intake air flow and it is linked by a cable to the accelerator pedal.
The throttle housing is secured to the intake manifold by four bolts (arrows).
The throttle valve is heated by engine coolant to prevent condensation from "icing". The throttle valve is "preset" and should not be adjusted.
Identifying Throttle Housing Bolts. Scheme 328
Throttle Position Sensor: A potentiometer is mounted on the throttle housing which provides the ECM with a voltage value (0-5v) that represents throttle angle position and rate of movement. The sensor receives its power supply from the ECM.
The Potentiometer is non-adjustable because the ECM "learns" the throttle angle voltage at idle speed. If the throttle position sensor is replaced, the adaptations must be cleared using the DIS/MoDIC.
If this input is defective, a fault code will be stored and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved. The ECM will still operate the engine using the Hot-Film Air Mass Meter and Engine RPM inputs.
Testing Throttle Position Sensor. Scheme 329
Idle Speed Control Valve: This valve regulates air bypassing the throttle valve to control the engine idle speed.
The valve is supplied with battery voltage from the ECM Relay. The Idle Air Actuator is a two-coil rotary actuator. The ECM is equipped with two final stage transistors which will alternate positioning of the actuator.
The final stages are "pulsed" simultaneously by the ECM which provides ground paths for the actuator. The duty cycle of each circuit is varied to achieve the required idle RPM.
Testing Idle Speed Control Valve. Scheme 330
If this component/circuits are defective, a fault code will be set and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved.
Hot-Film Air Mass Meter (HFM): The air volume input signal is produced electronically by the HFM which uses a heated metal film (180°C above intake air temperature) in the air flow stream.
The ECM Relay provides the operating voltage. As air flows through the HFM, the film is cooled changing the resistance which affects current flow through the circuit. The sensor produces a 1-5 volt varying signal. Based on this change the ECM monitors and regulates the amount of fuel injected.
Identifying Hot-Film Air Mass Meter (HFM). Scheme 331
If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved. The ECM will operate the engine using the Throttle Position and Engine RPM inputs.
Note. The HFM is non-adjustable.
Air Temperature Signal: This signal is needed by the ECM to correct the air volume input for changes in the intake air temperature. The sensor is located in the intake manifold behind the throttle housing.
The ECM provides the power supply to this component. The sensor decreases in resistance as the temperature rises and vice versa (NTC). The ECM monitors the applied voltage (5v), as air temperature changes the resistance value the voltage signal will vary (0-5v).
If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved. The ECM will operate the engine using the Engine Coolant Sensor input.
Identifying Air Temperature Signal. Scheme 332
Pressure Control Valve: The pressure control valve varies the vacuum applied to the crankcase ventilation depending on engine load. The valve is balanced between spring pressure and the amount of manifold vacuum.
The oil vapors exit the separator labyrinth (2) in the cylinder head cover (1). The oil vapors are drawn into the cyclone type liquid/vapor separator (3) regulated by the pressure control valve (5). The collected oil will drain back into the oil pan (4).
Identifying Pressure Control Valve Components. Scheme 333
At idle when the intake manifold vacuum is high, the vacuum reduces the valve opening allowing a small amount of crankcase vapors to be drawn into the intake manifold. At part to full load conditions when intake manifold vacuum is lower, the spring opens the valve and additional crankcase vapors are drawn into the intake manifold.
Locating Oil Vapors Exiting Separator Labyrinth In Cylinder Head Cover. Scheme 334
- Engine Oil Vapors
- Collective Drain Back Oil
- Oil Vapors to the Intake Manifold
Air flow into the engine is regulated by the Throttle Valve or the Idle Speed Control Valve. Both of these air "passages" are necessary for smooth engine operation from idle to full load. On the MS41.X system, the Throttle Valve is mechanically controlled and the Idle Speed Control Valve is electrically controlled. All of the ECM monitoring, processing and output functions are a result of regulated air flow.
Air Flow Principle. Scheme 335
The Throttle Position Sensor is monitored by the ECM for throttle angle position and rate of movement. As the throttle plate is opened, a rising voltage signal (up to 5v) requests acceleration and at what rate. The ECM will increase the volume of fuel injected into the engine, advance the ignition timing and decrease the Idle Speed Valve opening (air is now going by the throttle plate). The "full throttle" position indicates maximum acceleration to the ECM and in addition to the functions just mentioned, this will have an effect on the air conditioning compressor (covered in Performance Controls).
As the throttle plate is closed (integral springs), a decrease in voltage signals the ECM to activate fuel shut off if the RPM is above idle speed (coasting). The Idle Speed Control Valve will then be opened to maintain idle speed.
The ECM monitors the engine idle speed in addition the Throttle Position Sensor voltage. The voltage value is "learned" at the correct idle speed and if the voltage value has changed (mechanical wear of throttle plate or linkage), the ECM will adjust the Idle Speed Control Valve to maintain the correct idle speed based on the "new" voltage (the adaptations must be cleared using the DIS/MoDIC). If the Throttle Position input is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate when the OBD II criteria is achieved. The ECM will maintain engine operation based on the Hot-Film Air Mass Sensor and the Engine RPM Sensor.
The Idle Speed Control Valve is controlled by the ECM modulating the ground circuits to the two windings for opening and closing. By varying the duty cycle applied to the windings, the valve can be progressively opened or held steady to maintain the idle speed. If the Idle Speed Control Valve circuit is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate when the OBD II criteria is achieved.
There are additional factors that influence the ECM in regulating idle speed
Identifying ECM In Regulating Idle Speed. Scheme 336
- The RPM sensor input allows the ECM to monitor engine speed because of loads that cause idle fluctuations due to drag on the engine: power steering, thick oil (friction forces), etc.
- Cold engine temperature (coolant NTC) provides higher idle speed to raise temperature sooner.
- Vehicle speed informs ECM when the vehicle is stationary and requires idle maintenance.
- A/C on request from the climate control system (arming the ECM) and compressor engage (stabilize idle speed) acknowledgment.
- Range selector provides a Park/Neutral input to the ECM identifying when the vehicle is in a drive gear. This signal allows idle stabilizaton for the increased load on the engine.
The Hot-Film Air Mass Sensor sends a varying voltage (0-5v) to the ECM representing the measured amount of intake air volume. This input is used by the ECM to determine the amount of fuel to be injected. If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate when the OBD II criteria is achieved. The ECM will maintain engine operation based on the Throttle Position Sensor and Engine Speed Sensor.
The Air Temperature Signal allows the ECM to make a calculation of intake air temperature. The varying voltage input from the NTC sensor indicates the larger proportion of oxygen found in cold air, as compared to less oxygen found in warmer air. The ECM will adjust the amount of injected fuel because the quality of combustion depends on oxygen sensing ratio.
The ignition timing is also affected by air temperature. If the intake air is hot the ECM retards the base ignition timing to reduce the risk of detonation. If the intake air is cooler, the base ignition timing will be advanced. If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate when the OBD II criteria is achieved.