On-Board Diagnostics II / Inspection & Maintenance
INTRODUCTIONThe On-Board Diagnostics System OBD-II, is the second generation of on-board diagnostics that currently consists of the Check Engine Lamp and flash codes on BMW models.
The new OBD-II is designed to complement the I/M 240 regulations and testing procedures for emission control systems. Many of the changes to emission related systems and components that will be phased into production on all BMW models are a direct result of the I/M 240 requirements.
I/M 240 OVERVIEW
The I/M 240 stands for the Inspection and Maintenance program that is mandated by the EPA under the Clean Air Act of 1990. Approximately 20 States are scheduled to adopt this form of emission testing beginning as early as January 1995.
I/M 240 applies to states that classify as "Non-Attainment" areas or states that fail to comply with the EPA standards for clean air as specified by the Clean Air Act of 1990. States that do meet the clean air requirements can continue to use the current emission testing procedures (BAR 90) for monitoring purposes.
The I/M 240 testing will be carried out at state run or contracted facilities. The previous dealership and repair station testing will no longer be allowed in these non-attainment locations.
The new form of testing involves a 240 second test cycle where the vehicle is driven loaded on a dynamometer.
The test cycle includes periods of idle, cruise, acceleration and deceleration.
The exhaust gasses are measured using a process called "constant volume total sampling". The amount of HC, CO, CO2 and NOx produced are measured during the test.
Strict parameters for speed and time must be adhered to during the 4 minutes to obtain a valid test.
The measurement for the gasses, during the test cycle is carried out in "grams per mile" as compared to the BAR 90 method of "parts per million". This requires more sophisticated equipment than is currently used by most states in their emission testing. The equipment cost for an I/M 240 testing lane is approximately $250,000.
A second aspect of the I/M 240 test is the checking of the vapor recovery system. The vapor system is pressurized prior to the test cycle and checked for leaks. During the test cycle the purge control system is test for operation.
OBD II Connector Location View:
ON BOARD DIAGNOSTICS (OBD II) OVERVIEW
The OBD-II system expands the on-board monitoring and diagnostic capabilities of emission related components. The number of fault codes and related diagnostic information will be expanded.
The laws governing OBD-II require that all manufacturers install a read out connector, in the vehicle, that can be accessed using a scan tool. The law is specific as to the location, design and number of pins on the scan tool connector. The connector must be positioned inside the passenger's compartment and labeled for recognition.
The law also provides for standardization of terminology and fault code numbering for all manufacturers. This means that whatever make of vehicle is accessed through the scan tool the scan tool will give the same codes for each type of emission related fault.
This scan tool connector and fault code readout will not affect the diagnostic procedures, for BMW's, that are accessed through the DIS Tester or MoDiC.
The number and total scope of emission monitoring will increase. However, the troubleshooting procedures and fault explanations will continue to follow the format developed for the BMW testers.
The OBD-II standards have required the manufacturers to expand and improve the self monitoring capabilities of the powertrain control modules. These changes will be reflected in the design of the engine control systems as evidenced in the DME M5.2 and EML IIIs systems.
The changing requirements will also expand the fault troubleshooting and diagnostic procedures found on the DIS Tester and MoDiC.
The current list of OBD-II requirements is extensive and will likely continue to grow and change. There are currently provisions for over 200 separate fault codes that relate to the powertrain systems. The codes are very specific, for example there are 37 codes that retate to oxygen sensor circuit malfunctions.
The following list is an example of what the control modules will monitor for compliance with OBD-II:
- Input and output Oxygen content of the catalytic converter
- Engine for indications of misfire. The misfire must be identified by cylinder with the following data recorded; vehicle speed, engine RPM, load, engine temperature, integrator values and oxygen sensor closed/open loop operation.
- The vehicles purge system must be monitored for leaks or malfunctions at least once for every start/stop.
- Secondary air injection system must be monitored for proper operation.
- The fuel delivery system must be monitored for its ability to comply with emission standards.
- The voltage and switching rate of all oxygen sensors must be monitored as well as the O2 sensor heating.
- All other emission components and related component operation must be monitored.
Failures of any emission related components or systems will still be indicated through the Check Engine warning lamp in the cluster.
Each vehicle manufacturer must make emission related diagnostic and repair information available to the private repair industry. The J2008 standard calls for electronic access to this data base, possibly through CD-ROM distribution. The volume of information, for all manufacturers, prohibits any form of printed literature. The law is currently being contested by the manufactures, who are claiming infringement on proprietary information.
OBD II- CHECK ENGINE LAMP
The parameters for the Check Engine Lamp illumination are changed for vehicles equipped with the OBD II system. The total scope of OBD II monitoring includes all control modules than can influence the amount of exhaust emissions. This includes the engine control module (DME), the transmission control module (TCM) and the engine power control module (EML IIIs).
NOTE: These additional powertrain modules will have to be considered during troubleshooting when the Check Engine Lamp is illuminated.
Each of these modules monitor any input signals, the processing electronics and or final stages that when defective will cause the level of exhaust emissions to increase above the level that the vehicle was certified for.
The monitoring criteria for each signal or system depends on the degree of influence the signal has on the total volume of emissions produced by the engine.
There are specific differences in signal monitoring based on the monitoring time and load on the engine.
Faults that have a severe influence on emission levels will cause the Check Engine Lamp to illuminate immediately.
Other faults may require that the vehicle be driven two times with the fault present before the Check Engine Lamp illuminates.
In all cases the fault will be stored in the respective control module as soon as it is detected.
The following is an overview of faults that can cause the Check Engine Lamp to illuminate. The DME control module controls the illumination of the lamp. The AGS and EML control modules signal the DME for lamp illumination over the CAN line.
DME
- Processing electronics of the control module
- CAN interface signals
- Mass air flow meter
- Camshaft position sensor
- Fuel injectors
- Coolant and intake air temperature sensors
- Low or high battery voltage
- Catalytic converter monitoring
- Misfire detection for the ignition system
- Evaporative emission system
- Secondary air injection system
- Oxygen sensor - both pre and post catalytic converter sensors and heating circuits.
AGS
- Processing electronics of the control module
- CAN interface signals
- Shift solenoid and pressure regulator solenoids
- AGS supply voltage
- Transmission speed sensors
- Transmission range switch
EML IIIs
- Processing electronics of the control module
- CAN interface signals
- Throttle motor output control
- Throttle motor feedback signals