Principle of Operation
Principle Of Operation
Emissions Management controls evaporative and exhaust emissions. The ECM monitors the fuel storage system for evaporative leakage and controls the purging of evaporative fuel. The ECM monitors and controls the exhaust emissions by regulating the combustible mixture and after treating by injecting fresh air into the exhaust system. The catalytic converter further breaks down remaining combustible exhaust gases and is monitored by the ECM for catalyst efficiency.
The Evaporative Leakage Detection is performed on the fuel storage system by the DM TL pump which contains an integral DC motor that is activated by the ECM. The ECM monitors the pump motor operating current as the measurement for detecting leaks.
The pump also contains an ECM controlled change over valve that is energized closed during a Leak Diagnosis test. The ECM only initiates a leak diagnosis test every second time the criteria are met. The criteria is as follows:
- Engine OFF with ignition switched OFF.
- ECM still in active state or what is known as "follow up mode" (ECM Relay energized, ECM and components online for extended period after key off).
- Prior to Engine/Ignition switch OFF condition, vehicle must have been driven for a minimum of 20 minutes.
- Prior to minimum 20 minute drive, the vehicle must have been OFF for a minimum of 5 hours.
- Fuel Tank Capacity must be between 15 and 85% (safe approximation between 114 - 3/4 of a tank).
- Ambient Air Temperature between -7 °C & 35 °C (20 °F & 95 °F )
- Altitude < 2500 m (8,202 feet).
- Battery Voltage between 11.5 and 14.5 Volts.
When these criteria are satisfied every second time, the ECM will start the Fuel System Leak Diagnosis Test. The test will typically be carried out once a day i.e:, once after driving to work in the morning, when driving home in the evening, the criteria are once again met but the test is not initiated. The following morning, the test will run again.
PHASE 1 - REFERENCE MEASUREMENT
The ECM activates the pump motor, The pump pulls air from the filtered air inlet and passes it through a precise 1.0 mm reference orifice in the pump assembly.
The ECM simultaneously monitors the pump motor current flow. The motor current raises quickly and levels off (stabilizes)due to the orifice restriction. The ECM stores the stabilized amperage value in memory. The stored amperage value is the electrical equivalent of a 1.0 mm (0.040") leak.
PHASE 2 - LEAK DETECTION
The ECM energizes the Change Over Valve allowing the pressurized air to enter the fuel system through the Charcoal Canister. The ECM monitors the current flow and compares it with the stored reference measurement over a duration of time.
Once the test is concluded, the ECM stops the pump motor and immediately de-energizes the change over valve. This allows the stored pressure to vent thorough the charcoal canister trapping hydrocarbon vapor and venting air to atmosphere through the filter.
TEST RESULTS
The time duration varies between 45 & 270 seconds depending on the resulting leak diagnosis test results (developed tank pressure "amperage"/within a specific time period). However the chart below depicts the logic used to determine fuel system leaks.
If the ECM detects a leak, a fault will be stored and the "Malfunction Indicator Light" will be illuminated. Depending on the amperage measurement detected by the ECM, the fault code displayed will be "small leak" or "large leak".
If the vehicle was refueled and the filler cap was not properly installed, the "Check Filler Cap" message will be displayed.
The ECM detects refueling from a change in the fuel tank sending unit level via the Instrument Cluster. Upon a restart and driving the vehicle, the leakage test will be performed. If the ECM detects leakage, the "Check Filler Cap" light will illuminate in the lower left corner of the instrument cluster.
If the filler cap is installed and there is no leakage present the next time the leakage test is performed, the "Malfunction Indicator Light" will not be illuminated.
Evaporative Emission Purging is regulated by the ECM controlling the Evaporative Emission Valve. The Evaporative Emission Valve is a solenoid that regulates purge flow from the Active Carbon Canister into the intake manifold. The ECM Relay provides operating voltage, and the ECM controls the valve by regulating the ground circuit. The valve is powered open and closed by an internal spring.
The �purging" process takes place when:
- Oxygen Sensor Control is active
- Engine Coolant Temperature is >60 °C
- Engine Load is present
The Evaporative Emission Valve is opened in stages to moderate the purging.
- Stage 1 opens the valve for 10 ms (milli-seconds) and then closes for 150 ms.
- The stages continue with increasing opening times (up to 16 stages) until the valve is completely open.
- The valve now starts to close in 16 stages in reverse order
- This staged process takes 6 minutes to complete. The function is inactive for 1 minute then starts the process all over again.
- During the purging process the valve is completely opened during full throttle operation and is completely closed during deceleration fuel cutoff.
Evaporative Purge System Flow Check is performed by the ECM when the oxygen sensor control and purging is active. When the Evaporative Emission Valve is open the ECM detects a rich/lean shift as monitored by the oxygen sensors indicating the valve is functioning properly.
If the ECM does not detect a rich/lean shift, a second step is performed when the vehicle is stationary and the engine is at idle speed. The ECM opens and close the valve (abruptly) several times and monitors the engine rpm for changes. If there are no changes, a fault code will be set.
Fuel System Monitoring is an OBDII requirement which monitors the calculated injection time (ti) in relation to engine speed, load, and the pre catalytic converter oxygen sensor(s) signals as a result of the residual oxygen in the exhaust stream.
The ECM uses the pre catalyst oxygen sensor signals as a correction factor for adjusting and optimizing the mixture pilot control under all engine operating conditions.
Adaptation Values are stored by the ECM In order to maintain an "ideal" air/fuel ratio. The ECM is capable of adapting to various environmental conditions encountered while the vehicle is in operation (changes in altitude, humidity, ambient temperature, fuel quality, etc.).
The adaptation can only make slight corrections and can not compensate for large changes which may be encountered as a result of incorrect airflow or incorrect fuel supply to the engine.
Within the areas of adjustable adaption, the ECM modifies the injection rate under two areas of engine operation:
- During idle and low load mid range engine speeds (Additive Adaptation)
- During operation under a normal to higher load when at higher engine speeds (Multiplicative Adaptation).
These values indicate how the ECM is compensating for a less than ideal initial air/fuel ratio.
NOTE: If the adaptation value is greater than "0.0 ms" the ECM is trying to richen the mixture. If the adaptation value is less then "0.0 ms the ECM is trying to lean-out the mixture.
Catalyst Monitoring is performed by the ECM under oxygen sensor closed loop operation. The changing aidfuel ratio in the exhaust gas results in lambda oscillations at the pre-catalyst sensors. These oscillations are dampened by the oxygen storage activity of the catalysts and are reflected at the post catalyst sensors as a fairly stable signal (indicating oxygen has been consumed). Conditions for Catalyst Monitoring:
Requirements Status/Condition
- Closed loop operation YES
- Engine coolant temperature Operating Temp.
- Vehicle road speed 3 - 50 MPH (5 to 80 km/h)
- Catalyst temperature (calculated)* 350 °C to 650 °C
- Throttle angle deviation Steady throttle
- Engine speed deviation Steady/stable engine speed
- Average lambda value deviation Steady/stable load
* Catalyst temperature is an internally calculated value that is a function of load/air mass and time.
NOTE: The catalyst efficiency is monitored once per trip while the vehicle is in closed loop operation.
As part of the monitoring process, the pre and post O2 sensor signals are evaluated by the ECM to determine the length of time each sensor is operating in the rich and lean range.
If the catalyst is defective the post O2 sensor signal will reflect the pre O2 sensor signal (minus a phase shift/time delay), since the catalyst is no longer able to store oxygen.
The catalyst monitoring process is stopped once the predetermined number of cycles are completed, until the engine is shut-off and started again. After completing the next "customer driving cycle" whereby the specific conditions are met and a fault is again set, the "Malfunction Indicator Light" will be illuminated.
Oxygen Sensor Heating is controlled by the ECM to reduces warm up time and retain heat during low engine speed when the exhaust temperature is cooler.
Voltage is supplied from the ECM Relay and the ground circuit is provided by the ECM in pulse width modulation. By pulsing the ground circuit, the oxygen sensor heaters are gradually brought up to temperature. Each oxygen sensor has an individual circuit provided by the ECM.
During full throttle operation electrical heating is not required and is deactivated by the ECM.
Oxygen Sensor Heater Monitoring is part of the OBD II requirements requiring all oxygen sensors to be monitored separately for electrical integrity and heater operation. The heater function is monitored continuously while the vehicle is in closed loop operation, during activation by the ECM. An improperly/non operating heater will not allow the sensor signal to reach its predefined maximum and minimum thresholds which can:
- Result in delayed closed loop operation causing an impact on emission levels.
- Result in increased emission levels while in closed loop operation.
As part of the monitoring function for heater current and voltage, the circuit is also checked for an open, short to ground and short to B+ depending on the values of the current or voltage being monitored.
The ECM measures both sensor heater current and the heater voltage in order to calculate the sensor heater resistance and power. If the power of the heater is not within a specified range, a fault will be set. The next time the heater circuit is monitored and a fault is again present the "Malfunction Indicator Light" will be illuminated.
Secondary Air Injection is required to reduce HC and CO emissions while the engine is warming up. Immediately following a cold engine start (-10 to 40 °C) fresh air/oxygen is injected directly into the exhaust stream.
The temperature signal is provided to the ECM by the Air Temperature Sensor in the HFM.
The ECM provides a ground circuit to activate the Secondary Air Injection Pump Relay. The relay supplies voltage to the Secondary Air Injection Pump.
The single speed pump runs for approximately 90 seconds after engine start up.
* Below -10 °C the pump is activated briefly to "blow out" any accumulated moisture.
Secondary Air Injection Monitoring is performed by the ECM via the use of the pre-catalyst oxygen sensors. Once the air pump is active and is air injected into the exhaust system the oxygen sensor signals will indict a lean condition.
If the oxygen sensor signals do not change within a predefined time a fault will be set and identify the faulty bank(s). After completing the next cold start and a fault is again present the "Malfunction Indicator Light" will be illuminated.
Misfire Detection is part of the OBD II regulations the ECM must determine misfire and also identify the specific cylinder(s), the severity of the misfire and whether it is emissions relevant or catalyst damaging based on monitoring crankshaft acceleration.
Emission Increase:
- Within an interval of 1000 crankshaft revolutions, the ECM adds the the detected misfire events for each cylinder. If the sum of all cylinder misfire incidents exceeds the predeter mined value, a fault code will be stored.
- If more than one cylinder is misfiring, all misfiring cylinders will be specified and the individual fault codes for all misfiring cylinders and for multiple cylinder will be stored.
Catalyst Damage:
Within an interval of 200 crankshaft revolutions the detected number of misfiring events is calculated for each cylinder. The ECM monitors this based on load/rpm. If the sum of cylinder misfire incidents exceeds a predetermined value, a fault code is stored and the "Malfunction Indicator Light" will be illuminated.
If the cylinder misfire count exceeds the predetermined threshold the ECM will take the following measures:
- The oxygen sensor control will be switched to open loop.
- The cylinder selective fault code is stored.
- If more than one cylinder is misfiring the fault code for all individual cylinders and for multiple cylinders will be stored.
- The fuel injector to the respective cylinder(s) is deactivated.
The Integrated Ambient Barometric Pressure Sensor of the MS S54 is part of the ECM and is not serviceable. The internal sensor is supplied with 5 volts. In return it provides a linear voltage of approx. 2.4 to 4.5 volts representative of barometric pressure (altitude).
The MS S54 monitors barometric pressure for the following reasons:
- The barometric pressure signal along with calculated air mass provides an additional correction factor to further refine injection "on" time.
- Provides a base value to calculate the air mass being injected into the exhaust system by the Secondary Air Injection System. This correction factor alters the secondary air injection "on" time, optimizing the necessary air flow into the exhaust system.
E46 M3 Diagnostic Socket
For model year 2001 the E46 will eliminate the 20 pin diagnostic connector from the engine compartment. The 16 pin OBD II connector located inside the vehicle will be the only diagnosis port. The 16 pin OBD II connector has been in all BMWs since 1996 to comply with OBD regulations requiring a standardized diagnostic port.
Previously before 2001, only emissions relevant data could be extracted from the OBD connector because it did not provide access to TXD (D-bus). The TXD line is connected to pin 8 of the OBD II connector on vehicles without the 20 pin diagnostic connector.
The cap to the OBD II connector contains a bridge that bridges KL 30 to TXD and TXD II. This is to protect the diagnostic circuit integrity and prevent erroneous faults from being logged.
The OBD II connector is located in the drivers footwell to the left of the steering column.
Special tool 61 4 300 is used to connect to the 20 pin diagnostic lead of the DIS until the introduction of the DISplus.
Diagnostics via the OBD II Connector
