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 converters further break 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 DMTL 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 DMTL generates a pressure of 20-30 mbar in the fuel tank and evaporative system. The electrical current required for this is calculated by the ECM serves as the indirect value for the tank pressure.
The DMTL carries out a reference measurement before each measurement. This is performed by building up a pressure for 10-15 seconds using an internal orifice of 0.5 mm as a reference and the ECM monitors the current required by the pump motor (20-30 mA).
If a lower pressure is detected in the pressure build-up (low current draw) as compared to the reference measurement, this indicates a leak in the fuel tank/evaporative system. If a higher pressure is detected (higher current draw), the system does not have a leak.
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 is met. The criteria is as follows:
- Engine OFF with ignition switched OFF.
- ECM still in active stale 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.
- No faults in the ECM for DMTL/tank venting system.
- Fuel Tank Capacity must be between 10 and 90% (safe approximation between 1/4 - 3/4 of a tank).
- Ambient Air Temperature between -7°C & 35°C
- Altitude < 2500m (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 ie:, 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 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.
The time taken for the measurement is:
- 60-220 seconds if there are no leaks
- 200-360 seconds if there is a leak measuring 0.5 mm (small leak)
- 30-80 seconds it there is a leak measuring over 1 mm (large leak)
The evaporative emission valve is closed during the measurement. The time taken for the measurement is dependant on how much fuel there is in the tank.
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 30 & 360 seconds depending on the resulting leak diagnosis test results (developed tank pressure "amperage" within a specific time period).
When 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 While a Leak Diagnosis is Taking Place: The ECM detects refuelling during a leak diagnosis as a result of the pressure drop when the fuel filler cap is opened and the increase pressure while filling the tank is being filled.
In this case, the leakage diagnosis is interrupted. The solenoid valve in the DMTL is switched off and the tank pressure escapes through the activated carbon canister.
If refuelling does not take place immediately after the fuel filler cap has been opened, the system will detect a large leak and the a fault will be stored in the ECM. If refuelling is detected in the next driving cycle (increase in fuel level), the fault is cleared.
The ECM detects refueling from a change in the fuel tank sending unit level. If the filler cap was not properly installed, when the leakage test is performed and leakage is detected; the variable indicator lamp (shown to the right) and the "Please Close Filler Cap" Check Control message will be displayed.
If the filler cap is correctly installed and leakage is not present the next time the test is performed, the "Malfunction Indicator Light" will not be illuminated.
Starting with 2002 MY, a heating element was added to the DMTL pump to eliminate condensation.
The heater is provided battery voltage when KL15 is switched "on" and the ECM provides the ground path.
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:
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
- Valvetronic position deviation Steady
- Engine speed deviation Steady/stable engine speed
- Average lambda value deviation Steady/stable load
* Catalyst temperature is an ECM calculated value based on 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/consume oxygen. The catalyst monitoring process is stopped once the predetermined number of cycle 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.
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 indicate a lean condition. If the oxygen sensor signal do not change within a predefined time a fault will be set and identify the faulty bank(s) When diagnosing a Secondary Air Injection fault, in addition to the electric air pump an non-return valves always consider the following:
- Restricted air inlet to the pump.
- Restricted supply hoses to the non-return valves.
- Internal restrictions in the cylinder head passages into the exhaust ports.
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 emission 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.
- 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 ME 9.2 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 ME 9.2 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.
The Malfunction Indicator Light is illuminated when the OBD system (integral in the ECM) determines that a problem exists and a corresponding "Diagnostic Trouble Code" is stored in the ECM's memory. The Malfunction Indicator appears both in the instrument cluster upper center section (fixed) and in the Check Control Display (variable indicator). This light informs the driver of the need for service with a Check Control message displayed.
After fixing the problem the fault code is deleted to turn off the light. If the conditions that caused a problem are no longer present, the OBD system can turn off the light automatically. If the OBD system evaluates the component or system three consecutive times and no longer detects the initial problem, the dashboard light will turn off automatically.
The Malfunction Indicator Light will illuminate for the following reasons:
- Pre-drive check when the ignition is switched on (in the fixed location)
- Increased emissions (both fixed and variable indicator locations with message displayed)
- Engine fault - drive with moderation (variable indicator location with message displayed)
The Malfunction Indicator Light will illuminate with a "half shading" in the variable indicator location for the following reasons:
- Engine fault - with reduced power (with message displayed)
- Engine damage possible! (with message displayed)
Emissions Diagnosis
The "BMW Fast" (BMW fast access for service and testing) diagnosis concept is used in the E65/E66 for ME 9.2 ECM. This concept is based on the "Keyword Protocol 2000" (KWP 2000) diagnosis protocol defined as part of the ISO 14230 standard. Diagnosis communication takes place entirely on the basis of a transport protocol on the CAN bus. The Diagnosis bus is connected to the Central Gateway Module (ZGM).
Vehicle Diagnosis Access Point
The diagnosis tool is connected to the vehicle at the OBD diagnosis connector (On-Board Diagnosis). The connector is located behind a small cover in the drivers side kick panel trim. There is a black plastic cap that bridges KL30 to the D-bus when the connector is not being used. This cap must be removed before installing the diagnosis cable.
The TxD lead is located in pin 7 of the OBD socket and is connected directly to the ZGM.
The ZGM detects by means of the data transmission speed whether a BMW diagnosis tool (DISplus, MoDiC, GT-1) or an aftermarket scanner is connected.
The ECM allows access to different data depending on the diagnosis tool connected.
NOTE: when using an OBD scan tool for diagnosis, the transmission speed is 10.4 KBit/s.
Diagnosis Bus
The aim of diagnosis is to enable a Technician to reliably identify a defective component. By the use of appropriate hardware and monitoring software, the microprocessor of the diagnosis tool is able to detect faults in the ECM and its peripherals.
Faults identified are stored in the fault memory and can be read out using the Diagnosis Program. Data transfer between the vehicle and the diagnosis tool takes place via the Diagnosis bus (D bus).
The new features of the diagnosis bus are:
- Faster data transmission speed of 115 kBd.
- Central diagnosis access point (OBD connector).
- Single diagnostic cable (TxD II) for the entire vehicle.
- Omission of the TxD1 cable.
- Access to diagnosis functions requires "Authorization".
- Diagnosis protocol "KWP 2000" (Keyword Protocol 2000).
- Standardized diagnosis structure for all control units.
The ECM is not directly connected to the OBD diagnostic connector. The OBD diagnostic connector is connected to the ZGM. The ECM is connected to the ZGM (central gateway module) by the PT CAN bus. The ECM is also connected to the Valvetronic control module by the Lo CAN (local) bus. Valvetronic faults are stored in the ECM.