Principle Of Operation: Notes

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 Evaporative Leakage Detection (E36 and Z3)  is conducted by the ECM and can detect a leak as small as 1.0 mm (0.040") when the following conditions are met:

• No faults present. There are several fault codes relating to the evaporative system. In addition, the ECM also monitors the components for evaporative system operation. Any detected faults will be stored in the memory and the "CHECK ENGINE" light will illuminate when the OBD II criteria is achieved and the test will not conclude. 
• Engine coolant temperature must be < 80° C. 
• Current altitude >2500m (8,202 Feet). 
• Accumulated Canister Purge time < 360 seconds (6 minutes) since start of drive cycle. 
• Canister purge cycle times between 10 and 150 seconds in length (dependent on HC saturation). 
• Vehicle speed = 0 (vehicle at standstill). 
• Engine Speed = idle 

Once all of the testing criteria have been met, the ECM will start the test on the evaporative system. The test is carried out in the following sequence:

• The ECM reads and stores the current fuel tank pressure input value. 
• The Evaporative Emission Valve and shut-off valve are closed for approx. 8 seconds. 

• The ECM reads the pressure build up in the fuel tank. If the pressure build up is below a stored threshold value, the Evaporative Emission Valve is switched on for approximately 3 seconds. 
• The ECM reads the tank pressure after purging. If the pressure has dropped, the purge function is OK. 
• The Evaporative Emission Valve is switched OFF again for approximately 8 seconds. 
• The ECM reads the tank pressure again to verify pressure build up. 
• If the pressure build up is not within a stored value range, the ECM detects this as a leak within the evaporative system. 
• Depending on the degree of pressure build up, the ECM detects this as a leak within the evaporative system. 
• Following the test cycle, the shut-off valve is switched OFF and normal purge operation is resumed. 

The Evaporative Leakage Detection (98 MY E39)  uses a Leak Diagnosis Pump (LDP) to pressurize the fuel tank and the evaporative emission system (approx. 25mb.). The LDP equipped system is capable of detecting a leak as small as 0.5 mm. (0.020"). The LDP is located in the left rear (driver's side) fender well and is only replaceable as a complete component. The vacuum supply line (required for pump operation) is in the wiring harness from the engine compartment and runs down the driver's side of the vehicle.

The LDP is a unitized component that contains the following:

• Vacuum Chamber. 
• Pneumatic Pressure Chamber. 
• DME Activated Vacuum Solenoid. 
• Reed Switch - Providing A Switched Voltage Feedback Signal To The ECM. 

In the inactive state, the LDP diaphragm is at the bottom end (of down stroke). The diaphragm pushes a rod downward against spring pressure to open the canister vent valve.

This open valve serves as the filtered air inlet path for normal evaporative "breathing".

During Leak Testing of the evaporative system, the vent valve is sprung closed to block atmospheric venting. The Evaporative Emission Valve is also sprung closed to seal the system.

During every engine cold start the LDP solenoid is energized by the ECM. Engine manifold vacuum enters the upper chamber of the LDP to lift up the spring loaded diaphragm.

As the diaphragm is lifted it draws in ambient air through the filter and into the lower chamber of the LDP through the one way valve.

The solenoid is then de-energized, spring pressure closes the vacuum port blocking the engine vacuum and simultaneously opens the vent port to the balance tube which releases the captive vacuum in the upper chamber.

This allows the compressed spring to push the diaphragm down, starting the "limited down stroke". The air that was drawn into the lower chamber of the LDP during the upstroke is forced out of the lower chamber and into the fueltank/evaporative system.

• This electrically controlled repetitive up/down stroke is cycled repeatedly building up a total pressure of approximately +25mb in the evaporative system. After sufficient pressure has built up (LDP and its cycling is calibrated to the vehicle), the leak diagnosis begins and lasts about 100 seconds. 
• The upper chamber contains an integrated reed switch that produces a switched high/low voltage signal that is monitored by the ECM. The switch is opened by the magnetic interruption of the metal rod connected to the diaphragm is in the top dead center position. 
• The repetitive up/down stroke is confirmation to the ECM that the valve is functioning. The ECM also monitors the length of time it takes for the reed switch to open, which is opposed by pressure under the disarrayed in the lower chamber. The LDP is still cycled, but at a frequency that depends upon the rate of pressure loss in the lower chamber. 
• If the pumping frequency is below parameters, there is no leak present. If the pumping frequency is above parameters, this indicates sufficient pressure can not build up in the lower chamber and evaporative system, indicating a leak. 

The chart represents the diagnostic leak testing time frame in seconds. When the ignition is switched on, the ECM performs a "static check" of circuit integrity to the LDP pump including the reed switch.

• On cold engine start up, the pump is activated for the first 27 seconds at approximately 166-200 Hz. This rapid pumping phase is required to pressurized the evaporative components. 
• Once pressurized, the build up phase then continues from 27-38 seconds. The ECM monitors the system through the reed switch to verify that pressure has stabilized. 
• The measuring phase for leak diagnosis lasts from 38-63 seconds. The pump is activated but due to the pressure build up under the diaphragm, the pump moves slower, if the pump moves quickly, this indicates a lack of pressure of a leak. The registers as a fault in the ECM's. 
• From 63-100 seconds the pump is deactivated, allowing full down stroke of the diaphragm and rod. At the extreme bottom of rod travel, the canister vent valve is pushed open relieving pressure and allowing normal purge operation when needed. 

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 (mill-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 on the E39. 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. The E36 and Z3 is checked during the Evaporative Leakage Test.

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 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.

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 

1. Yes 
2. Engine Coolant Temperature 
3. Operating Temperature 
4. Vehicle Road Speed 
5. 3-50 MPH (5 to 80 Km/h) 
6. Catalyst Temperature (Calculated) 
7. 350°C to 650° C 
8. Throttle Angle Deviation 
9. Steady Throttle 
10. Engine Speed Deviation 
11. Steady / Stable Engine Speed 
12. Average Lambda Value Deviation 
13. Steady / Stable Load 

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 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 "CHECK ENGINE" 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. Below -10° C the pump is activated briefly to "blow out" any accumulated moisture.

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.

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 air is 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 (E36 328i and E39).

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 detected the "CHECK ENGINE" Light will be illuminated when the OBD II criteria is achieved.

Misfire Detection  is part of the OBD II 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 "CHECK ENGINE" Light will be illumnated. 
• If more than one cylinder is misfiring, all of the misfiring cylinders will be specified and the individual fault codes for each misfiring cylinder, or multiple cylinders will be stored. The "CHECK ENGINE" 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 "CHECK ENGINE" 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 selected 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. 

• 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. 

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 check engine light is performed in accordance with the regulations set forth in CARB mail-out 1968.1 and as demonstrated via the Federal Test Procedure (FTP). The following page provides several examples of when and how the "CHECK ENGINE" 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 "CHECK ENGINE" 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, the ECM counts the third drive cycle as the "next consecutive" drive cycle. The "CHECK ENGINE" light to be illuminated. 
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 "CHECK ENGINE" Light to be illuminated. 
5. Once the "CHECK ENGINE" 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 the 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 DIS, MODIC, or Scan Tool. 

With the use of a universal scan tool, connected to the "OBD" DLC an SAE standardized DTC can be obtained, along with the condition associated with the illumination of the "CHECK ENGINE" Light. Using the DIS or MODIC, a fault code and the conditions associated with its setting can be obtained prior to the illumination of the "CHECK ENGINE" Light.