Part 1
ENGINE OBD II MONITORSOBD II Overview
The California Air Resources Board (CARB) began regulating OBD systems for vehicles sold in California beginning with the 1988 model year. The initial requirements, known as OBD-I, required identifying the likely area of concern with regard to the fuel metering system, exhaust gas recirculation (EGR) system, emission-related components and the PCM. A malfunction indicator lamp (MIL) was required to illuminate and alert the driver of the malfunction and the need to repair the emission control system. A DTC was required to assist in identifying the system or component associated with the malfunction.
Starting with the 1994 model year, both CARB and the Environmental Protection Agency (EPA) mandated enhanced OBD systems, commonly known as OBD-II. The objectives of the OBD-II system are to improve air quality by reducing high in-use emissions caused by emission-related malfunctions, reducing the time between the occurrence of a malfunction and its detection and repair, and assisting in the diagnosis and repair of emission-related problems.
OBD-II Systems
The OBD II system monitors virtually all emission control systems and components that can affect tailpipe or evaporative emissions. In most cases, malfunctions must be detected before emissions exceed 1.5 times the applicable 120,000 or 150,000 mile emission standards. If a system or component exceeds emission thresholds or fails to operate within a manufacturer's specifications, a DTC is stored and the MIL is illuminated within 2 drive cycles.
The OBD-II system monitors for malfunctions either continuously, (regardless of driving mode), or non-continueously, (once per drive cycle during specific drive modes). A pending DTC is stored in the PCM keep alive memory (KAM) when a malfunction is initially detected. Pending DTCs are displayed as long as the malfunction is present. Note that OBD regulations required a complete malfunction-free monitoring cycle to occur before erasing a pending DTC. This means that a pending DTC is erased on the next power-up after a malfunction-free monitoring cycle. However, if the malfunction is still present after 2 consecutive drive cycles, the MIL is illuminated. Once the MIL is illuminated, 3 consecutive drive cycles without a malfunction detected are required to extinguish the MIL. The DTC is erased after 40 engine warm-up cycles once the MIL is extinguished.
In addition to specifying and standardizing much of the diagnostics and MIL operation, OBD II requires the use of a standard Diagnostic Link Connector (DLC), standard communication links and messages, standardized DTCs and terminology. Examples of standard diagnostic information are freeze frame data and Inspection Maintenance (IM) readiness indicators.
Freeze frame data describes data stored in the KAM at the point the malfunction is initially detected and the pending DTC is stored. Freeze frame data consists of parameters such as engine RPM, engine load, vehicle speed or throttle position. Freeze frame data is updated when the malfunction is detected again on a subsequent drive cycle and a confirmed DTC is stored; however, a previously stored freeze frame is overwritten if a higher priority fuel or misfire malfunction is detected. This data is accessible with the scan tool to allow duplicating the conditions when the malfunction occurred in order to assist in repairing the vehicle.
OBD I/M readiness indicators show whether all of the OBD monitors have been completed since the last time the KAM or the PCM DTC(s) have been cleared. Mazda stores a DTC P1000 and blinks the MIL after 15 seconds of key-on engine-off time to indicate that some monitors have not completed. In some states, it may be necessary to carry out an OBD check in order to renew a vehicle registration. The IM readiness indicators must show that all monitors have been completed prior to the OBD check.
The following monitor descriptions provide a general description of each OBD monitor. In these descriptions, the monitor strategy, hardware, testing requirements, and methods are presented to provide an overall understanding of monitor operation. An illustration of each monitor may also be provided. These illustrations should be used as typical examples and are not intended to represent all possible vehicle configurations.
Each illustration depicts the PCM as the main focus with primary inputs and outputs for each monitor. The icons to the left of the PCM represent the inputs used by each of the monitor strategies to enable or activate the monitor. The components and subsystems to the right of the PCM represent the hardware and signals used while carrying out the tests and the systems being tested. The CCM illustration has numerous components and signals involved which are shown generically. When referring to the illustrations, match the numbers to the corresponding numbers in the monitor descriptions for a better comprehension of the monitor and associated DTCs.
These icons are used in the illustrations of the OBD monitors and through out this.
Catalyst Efficiency Monitor
The catalyst efficiency monitor uses an oxygen sensor before and after the catalyst to infer the hydrocarbon (HC) efficiency based on the oxygen storage capacity of the catalyst. During monitor operation the PCM calculates the length of the signal while the sensors are switching. Under normal closed-loop fuel conditions, high efficiency catalysts have significant oxygen storage. This makes the switching frequency of the rear heated oxygen sensor (HO2S) very slow and reduces the amplitude, which provides for a shorter signal length. The front HO2S switches more frequently with greater amplitude, which provides for a longer signal length. As the catalyst efficiency deteriorates due to thermal and chemical deterioration, its ability to store oxygen declines. The post-catalyst or downstream HO2S signal begins to switch more rapidly with increasing amplitude and signal length, approaching the switching frequency, amplitude, and signal length of the pre-catalyst or upstream HO2S. The predominant failure mode for high mileage catalysts is chemical deterioration (phosphorus deposits on the front brick of the catalyst), not thermal deterioration.
In order to assess catalyst oxygen storage, the catalyst monitor counts the number of front HO2S switches during part-throttle, closed-loop fuel conditions after the engine is warmed-up and the inferred catalyst temperature is within limits. The number of front switches are accumulated, depending on the calibration, in up to 3 different air mass regions or cells. While catalyst monitoring entry conditions are being met, the front and rear HO2S signal lengths are continually being calculated. When the required number of front switches has accumulated in each cell, the total signal length of the rear HO2S is divided by the total signal length of the front HO2S to compute a catalyst index ratio. An index ratio near 0.0 indicates high oxygen storage capacity, hence high HC efficiency. An index ratio near 1.0 indicates low oxygen storage capacity, hence low HC efficiency. If the actual index ratio exceeds the threshold index ratio, the catalyst is considered failed.
Inputs from engine coolant temperature (ECT) or cylinder head temperature (CHT), intake air temperature (IAT), mass air flow (MAF), crankshaft position (CKP), throttle position (TP), and vehicle speed sensors are required to enable the Catalyst Efficiency Monitor.
Typical monitor entry conditions:
- Minimum 330 seconds since start-up at 21°C (70°F).
- Engine coolant temperature is between 76.6 - 110°C (170 - 230°F)
- Intake air temperature is between -7 - 82°C (20 - 180°F)
- Time since entering closed-loop is 30 seconds
- Inferred rear HO2S temperature of 482°C (900°F)
- EGR is between 1% and 12%
- Part throttle, maximum rate of change is 0.2 volts/0.050 sec
- Vehicle speed is between 8 and 112 km/h (5 and 70 mph)
- Fuel level is greater than 15%
- First Air Flow Cell
- Engine RPM 1,000 to 1,300 RPM
- Engine load 15 to 35%
- Inferred catalyst temperature 454 - 649°C (850 - 1,200°F)
- Number of front HO2S switches is 50
- Second Air Flow Cell
- Engine RPM 1,200 to 1,500 RPM
- Engine load 20 to 35%
- Inferred catalyst temperature 482 - 677°C (900 - 1,250°F)
- Number of front HO2S switches: 70
- Third Air Flow Cell
- Engine RPM 1,300 to 1,600 RPM
- Engine load 20 to 40%
- Inferred catalyst temperature 510 - 704°C (950 - 1,300°F)
- Number of front HO2S switches is 30
The DTCs associated with this test are DTC P0420 (Bank 1 or Y-pipe system) and P0430 (Bank 2). Because an exponentially weighted moving average algorithm is used to determine a malfunction, up to 6 driving cycles may be required to illuminate the MIL during normal customer driving. If the KAM is reset or the battery is disconnected, a malfunction illuminates the MIL in 2 drive cycles.
General Catalyst Monitor Operation
Monitor execution is once per drive cycle. The typical monitor duration is 700 seconds. In order for the catalyst monitor to run, the HO2S monitor must be complete and the secondary AIR and EVAP system functional with no stored DTCs. If the catalyst monitor does not complete during a particular driving cycle, the already accumulated switch/signal data is retained in the KAM and is used during the next driving cycle to allow the catalyst monitor a better opportunity to complete.
Rear HO2S can be located in various configurations to monitor different kinds of exhaust systems. In-line engines and many V-engines are monitored by their individual bank. A rear HO2S is used along with the front, fuel control HO2S for each bank. Two sensors are used on an in-line engine and 4 sensors are used on a V-engine. Some V-engines have exhaust banks that combine into a single underbody catalyst. These systems are referred to as Y-pipe systems. They use only 1 rear HO2S along with the 2 front, fuel-control HO2S. The Y-pipe system uses 3 sensors in all. For Y-piped systems, the 2 front HO2S signals are combined by the PCM software to infer what the HO2S signal would have been in front of the monitored catalyst. The inferred front HO2S signal and the actual single, rear HO2S signal is then used to calculate the index ratio.
Exhaust systems that use an underbody catalyst without a downstream/rear HO2S are not monitored by the catalyst efficiency monitor.
Most vehicles that are part of the low emission vehicle (LEV) catalyst monitor phase-in, monitor less than 100% of the catalyst volume. Often this is the first catalyst brick of the catalyst system. Partial volume monitoring is done on LEV and ultra low emission vehicle (ULEV) vehicles in order to meet the 1.75 emission standard. The rationale for this strategy is that the catalyst nearest the engine deteriorate first, allowing the catalyst monitor to be more sensitive and illuminate the MIL correctly at lower emission standards.
Many applications that use partial-volume monitoring place the rear HO2S after the first light-off catalyst can or after the second catalyst can in a 3-can per bank system. (A few applications placed the HO2S in the middle of the catalyst can, between the first and second bricks).
Some partial zero emission vehicles (PZEV) use 3 sets of HO2S per engine bank. The front sensors or stream 1 (HO2S11/HO2S21) are the primary fuel control sensors. The next sensors downstream or stream 2 in the exhaust are used to monitor the light-off catalyst (HO2S12/HO2S22). The last sensors downstream or stream 3 in the exhaust (HO2S13/HO2S23) are used for very long term fuel trim in order to optimize catalyst efficiency (fore aft oxygen sensor control).
For additional heated oxygen sensor information, see HEATED OXYGEN SENSOR (HO2S) MONITOR.
Catalyst Efficiency Monitor
Cold Start Emission Reduction Monitor
Overview
The cold start emission reduction monitor is an on-board strategy designed for vehicles that meet the low emissions vehicle-II (LEV-II) emissions standards. The monitor works by validating the operation of the components of the system required to achieve the cold start emission reduction strategy. There are 2 types of monitors:
- cold start emission reduction component monitor
- cold start emission reduction system monitor
Cold Start Emission Reduction Component Monitor
Two different tests are carried out during the cold start emission reduction component monitor. The low idle airflow test which checks the performance of the idle air control strategy and the spark timing monitor test which checks the spark timing strategy.
Low Idle Air Flow Test
When the cold start emission reduction monitor is enabled, the PCM commands the idle air control system to increase the RPM, which elevates engine air flow. While this cold start emission reduction elevated air flow is requested, the low idle air flow test compares the measured idle air flow from the mass air flow (MAF) sensor to the commanded idle air control strategy. For the purpose of detecting low air flow malfunctions, the low air flow test uses the measured air flow and the commanded air flow to create a low air flow index.
Low Idle Air Flow Test Operation
- DTC: P050A cold start idle air control system performance
- Monitor execution: Once per driving cycle, from start up with the cold start emissions reduction active
- Monitor sequence: none
- Monitoring duration: 7 seconds
Low Idle Air Flow Test Entry Conditions
- Engine coolant temperature is between 4.4°C (40°F) and 82.2°C (180°F)
- Barometric pressure is between 76.2 kPa (22.5 in-Hg) and 105 kPa (31 in-Hg)
- Engine off soak time is at least 50 minutes
- Throttle is at closed position
Spark Timing Monitor Test
The PCM is equipped with a spark conduction capture circuit which measures the timing and duration of the spark delivered by processing the fly back voltage signal from the primary side of the ignition coil. When the cold start emission reduction monitor is enabled, the spark control strategy in the PCM commands the spark timing strategy to retard the spark timing. While retarded spark timing is requested, the spark timing monitor compares the measured spark timing from the spark conduction capture circuit to the commanded spark timing from the spark control strategy. For the purpose of detecting spark timing failures, the spark timing monitor increments a fault filter if the measured spark timing is advanced by more than 5 degrees from the commanded spark timing. A failure is indicated if the fault filter exceeds a value of 200, equivalent to a failure duration of approximately 4 seconds.
Spark Timing Monitor Test Operation
- DTC: P050B cold start ignition timing performance
- Monitor execution: once per driving cycle, from start up with the cold start emission reduction monitor active
- Monitor sequence: none
- Monitoring duration: 7 seconds
Spark Timing Monitor Test Entry Conditions
- Engine speed is between 400 RPM and 2,000 RPM
- Engine position and cylinder identification are synchronized
- There are no malfunctions with the ignition coils primary circuits
Cold Start Emission Reduction System Monitor
The PCM uses the cold start emission reduction system monitor to calculate the actual catalyst warm up temperature during a cold start. The actual catalyst warm up temperature calculation uses measured engine speed, measured air mass and commanded spark timing inputs to the PCM. The PCM then compares the actual temperature to the expected catalyst temperature model. The expected catalyst temperature model calculation uses desired engine speed, desired air mass and desired spark timing inputs to the PCM. The difference between the actual and expected temperatures is reflected in a ratio. This ratio is a measure of how much loss of catalyst heating occurred over the period of time and when compared with a calibrated threshold it helps the PCM to determine if the cold start emission reduction system is working correctly. This ratio correlates to tailpipe emissions, and a malfunction indicator lamp (MIL) illuminates when the calibrated threshold is exceeded. The monitor is disabled if a malfunction is present in any of the sensors or systems used for expected catalyst temperature model calculation.
Cold Start Emission Reduction System Monitor Test Operation
- DTC: P050E cold start engine exhaust temperature out of range
- Monitor execution: once per driving cycle, from start up with the cold start emission reduction monitor active
- Monitor sequence: the monitor collects data during first 15 seconds of the cold start
- Monitoring duration: the monitor completes 300 seconds after initial engine start
Cold Start Emission Reduction System Monitor Entry Conditions
- Engine coolant temperature at the start of the monitor is between 1.67°C (35°F) and 37.78°C (100°F)
- Barometric pressure is above 74.5 kPa (22 in-Hg) - Catalyst temperature at the start of the monitor is between 1.67°C (35°F) and 51.67°C (125°F)
- Fuel level is above 15%
- Power take-off operation is disabled
Comprehensive Component Monitor (CCM)
The CCM monitors for malfunctions in any powertrain electronic component or circuit that provides input or output signals to the PCM that can affect emissions and is not monitored by another OBD II monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or correct range of values. Where feasible, inputs are also checked for rationality, outputs are also checked for correct functionality.
The CCM covers many components and circuits and tests them in various ways depending on the hardware, function, and type of signal. For example, analog inputs such as throttle position or engine coolant temperature are typically checked for opens, shorts and out-of-range values. This type of monitoring is carried out continuously. Some digital inputs like vehicle speed or crankshaft position rely on rationality checks - checking to see if the input value makes sense at the current engine operating conditions. These types of tests may require monitoring several components and can only be carried out under appropriate test conditions.
Outputs such as coil drivers are checked for opens and shorts by monitoring a feedback circuit or smart driver associated with the output. Other outputs, such as relays, require additional feedback circuits to monitor the secondary side of the relay. Some outputs are also monitored for correct function by observing the reaction of the control system to a given change in the output command. An idle air control solenoid can be functionally tested by monitoring the idle RPM relative to the target idle RPM. Some tests can only be carried out under the appropriate test conditions. For example, the transmission shift solenoids can only be tested when the PCM commands a shift.
The following is an example of some of the input and output components monitored by the CCM. The components monitor may belong to the engine, ignition, transmissions, air conditioning, or any other PCM supported subsystem.
1. Inputs:
1. Air conditioning (ACP) pressure sensor
2. Camshaft position (CMP) sensor
3. Crankshaft position (CKP) sensor
4. Engine coolant temperature (ECT) sensor or cylinder head temperature (CHT) sensor
5. Engine oil temperature (EOT) sensor
6. Fuel rail pressure (FRP) sensor
7. Fuel rail temperature (FRPT) sensor
8. Fuel tank pressure (FTP) sensor
9. Intake air temperature (IAT) sensor
10. Mass air flow (MAF) sensor
11. Throttle position (TP) sensor
2. Outputs:
1. EVAP canister purge valve
2. EVAP canister vent (CV) solenoid
3. Fuel injector
4. Fuel pump (FP)
5. Idle air control (IAC)
6. Intake manifold runner control (IMRC)
7. Shift solenoid
8. Torque converter clutch (TCC) solenoid
9. Wide open throttle A/C cutout (WAC)
Comprehensive Component Monitor (CCM)
3. CCM is enabled after the engine starts and is running. A DTC is stored in KAM and the MIL is illuminated after 2 driving cycles when a malfunction is detected. Many of the CCM tests are also carried out during an on-demand self-test.