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 vapors. 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 MS45 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 initiates a leak diagnosis test every 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 � � of a tank).
^ Ambient Air Temperature between 4°C & 35°C (40°F & 95°F)
^ Altitude < 2500m (8,202 feet).
^ Battery Voltage between 10.95 and 14.5 Volts
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 0.5 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 0.5 mm (0.020") 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 deenergizes 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 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.
Refuelling during the test will interrupt the diagnosis and the DM TL will be de-energized. The ECM detects this by:
^ Pressure drop when filler cap is removed
^ Rise in pressure due to refuelling
If refuelling does not take place immediately after opening the filler cap (pressure rise missing), a large leak is detected.
If the vehicle was refueled and the filler cap was not properly installed, the Check Filler Cap message will be displayed in the instrument cluster for 20 seconds.
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 (additional detailed information on page 82 of Workshop Hints).
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 >67° 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 (mil. 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 rem for changes. If there are no changes, a fault code will be set.
Fuel System Monitoring is performed by the ECM which verifies the calculated injection time (ti) in relation to engine speed, load and the oxygen sensor signal as a result of the residual oxygen in the exhaust stream.
The ECM uses the oxygen sensor signal 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 adaptation, 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 Additive (% Multiplicative), the ECM is trying to richen the mixture. If the adaptation value is less then "0.0" Additive (% Multiplicative), the ECM is trying to lean out the mixture.
Catalyst Monitoring is performed by the ECM under oxygen sensor closed loop operation. The changing air/fuel ratio in the exhaust gas results in lambda oscillations at the precatalyst 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:
^ Catalyst temperature is an internally calculated value that is a function of load/air mass and time.
As part of the monitoring process, the pre and post 0Q 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 0Q 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 shutoff 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.
Note: The catalyst efficiency is monitored once per trip while the vehicle is in closed loop operation.
Secondary Air Injection is required to reduce HO and CO emissions while the engine is warming up. Immediately following a cold engine start (10 to 60°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 HEM*.
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 precatalyst oxygen sensors. Once the air pump is active and is air injected into the exhaust system the oxygen sensor signals will indicate a lean condition (up to 16 seconds).
If the oxygen sensor signals do not change within a predefined time a fault will be set and identify the faulty bank.
If the additional oxygen is not detected for two consecutive cold starts, the ECM determines a general fault with the function of the secondary air injection system. After completing the next cold start and a fault is again present the Malfunction Indicator Light will be illuminated when the OBD II criteria is achieved.
Misfire Detection is part of the OBD 11 regulations the ECM must determine misfire and also identify the specific cylinder(s). The ECM must also determine 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 detected misfire events for each cylinder. If the sum of all cylinder misfire incidents exceeds the predetermined value, a fault code will be stored and the Malfunction Indicator Light will be illuminated.
^ If more than one cylinder is misfiring, all misfiring cylinders will be specified and the individual fault codes for each misfiring cylinder, or multiple cylinders will be stored. The Malfunction Indicator Light will be illuminated.
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 Catalyst Damaging 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 mis firing the fault code for all individual cylinders and for multiple cylinders will be stored.
^ The fuel injector to the respective cylinder(s) is deactivated.
Electrically Heated Thermostat
Model specific variants of the electrically heated thermostat are equipped on all LEV/ULEV compliant engines. This thermostat allows the engine to run more efficiently than conventional thermostats improving fuel economy.
The ECM also electrically activates the thermostat to lower the engine coolant temperatures based on monitored conditions. It is both a conventionally functioning and ECM controlled thermostat (two stage operation). ECM control adds heat to the wax core causing the thermostat to open earlier than its mechanical temperature rating providing increased coolant flow.
Conventional Function: The thermostat begins to open at 103°C. This is at the inlet side of the water pump and represents the temperature of the coolant entering the engine. Before the 103°C temperature is realized, the coolant is circulated through the engine block by the water pump.
After the temperature reaches 103°C it is maintained as the inlet temperature by the thermostat. The coolant temperature at the water pump engine outlet is approximately 110°C. The additional 7°C is achieved after the coolant has circulated through the block.
The operating temperature of the engine will remain within this range as long as the engine is running at part load conditions and the engine coolant temperature does not exceed - - Cow
ECM Control
Electric thermostat activation is based on the following parameters:
^ Engine temperature > 113°C
^ Radiator Coolant Outlet Temperature
^ Load signal ti > 5.8 ms
^ Intake air temp > 52°C
^ Vehicle speed > 110 MPH
When one or more of these monitored conditions is determined, the ECM activates (switched ground) the thermostat circuit. The activated heating element causes the wax core in the thermostat to heat up and open the thermostat increasing coolant circulation through the radiator which brings the engine temperature down.
The temperature of the coolant at the inlet side of the water pump will drop to approximately 85°C and the temperature at the outlet side will drop to approximately 103°C when activated.
The Malfunction Indicator Light (MIL) will be illuminated under the following conditions:
^ Upon the completion of the next consecutive driving cycle where the previously faulted system is monitored again and the emissions relevant fault is again present.
^ Immediately if a Catalyst Damaging fault occurs (see Misfire Detection).
The illumination of the light is performed in accordance with the Federal Test Procedure (FTP) which requires the lamp to be illuminated when:
^ A malfunction of a component that can affect the emission performance of the vehicle occurs and causes emissions to exceed 1.5 times the standards required by the (FTP).
^ Manufacturer defined specifications are exceeded.
^ An implausible input signal is generated.
^ Catalyst deterioration causes Hc emissions to exceed a limit equivalent to 1.5 times the standard (FTP).
^ Misfire faults occur.
^ A leak is detected in the evaporative system, or purging is defective.
^ ECM fails to enter closed loop oxygen sensor control operation within a specified time interval.
^ Engine control or automatic transmission control enters a limp home operating mode.
^ Ignition is on (KL15) position before cranking = Bulb Check Function.
Within the BMW system the illumination of the Malfunction Indicator Light is performed in accordance with the regulations set forth in CARE mail out 1968.1 and as demonstrated via the Federal Test Procedure (FTP).
The following page provides several examples of when and how the Malfunction Indicator Light is illuminated based on the customer drive cycle.
1. A fault code is stored within the ECM upon the first occurrence of a fault in the system being checked.
2. The Malfunction Indicator Light will not be illuminated until the completion of the second consecutive customer driving cycle where the previously faulted system is again monitored and a fault is still present or a catalyst damaging fault has occurred.
3. If the second drive cycle was not complete and the specific function was not checked as shown in the example, the ECM counts the third drive cycle as the next consecutive drive cycle. The Malfunction Indicator Light is illuminated if the function is checked and the fault is still present.
4. If there is an intermittent fault present and does not cause a fault to be set through multiple drive cycles, two complete consecutive drive cycles with the fault present are required for the Malfunction Indicator Light to be illuminated.
5. Once the Malfunction Indicator Light is illuminated it will remain illuminated unless the specific function has been checked without fault through three complete consecutive drive cycles.
6. The fault code will also be cleared from memory automatically if the specific function is checked through 40 consecutive drive cycles without the fault being detected or with the use of either the DlSplus, GT1 or Scan tool.
NOTE: In order to clear a catalyst damaging fault (see Misfire Detection) from memory, the condition must be evaluated for 80 consecutive cycles without the fault reoccurring.