Part 1

ENGINE OBD II MONITORS
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 50,000 or 100,000 mile emission standards. If a system or component exceeds emission thresholds or fails to operate within a manufacturer's specifications, a DTC will be stored and the multifunction indicator lamp (MIL) will be illuminated within two driving 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 DTC is stored in the powertrain control module (PCM) keep alive memory (KAM) when a malfunction is initially detected. In most cases the MIL is illuminated after two consecutive drive cycles with the malfunction present. Once the MIL is illuminated, three 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 data 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 KAM at the point the malfunction is initially detected. Freeze frame data consists of parameters such as engine rpm and load, state of fuel control, spark, and warm-up status. Freeze frame data is stored at the time the first malfunction is detected, however, previously stored conditions will be replaced if a fuel or misfire fault is detected. This data is accessible with the WDS or equivalent tester to assist in repairing the vehicle.

OBD II inspection maintenance (IM) readiness indicators show whether all of the OBD II monitors have been completed since KAM was last cleared. Mazda also stores a P1000 DTC to indicate that some monitors have not completed. In some states, it may be necessary to perform 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.

Catalyst Efficiency Monitor - Federal Test Procedure
The federal test procedure catalyst monitor monitors the catalyst system for deterioration and illuminates the MIL when tailpipe emissions exceed the appropriate hydrocarbon (HC) emission thresholds. It is called the federal test procedure (FTP) catalyst monitor because it must complete during a standard emission test. This monitor relies on the front and rear heated oxygen sensors (HO2S) to infer catalyst efficiency based upon oxygen storage capacity. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the rear HO2S quite slow compared with the frequency of the front HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines, and the rear HO2S begins to switch more rapidly, approaching the frequency of the front sensor. In general, as catalyst efficiency decreases, the switch ratio increases from a switch rat b of 0 for a low mileage catalyst to a- switch ratio of 0.8 or 0.9 for a low-efficiency catalyst.

Many low emission California vehicles will monitor substantially less than the entire catalyst volume in order to meet the stringent catalyst monitoring malfunction thresholds. In many cases, only the front, light-off catalyst is monitored.

Front and rear HO2S switches are counted under specified closed loop fuel conditions. After the required number of front switches are obtained, a rear-to-front HO2S switch ratio is calculated. The switch ratio is compared against a threshold value. If the switch ratio is greater than the emission threshold, the catalyst has failed. Inputs from the engine coolant temperature (ECT) (warmed up engine), intake air temperature (IAT) (not at extreme ambient temperatures), mass air flow (MAF) (greater than minimum engine load), vehicle speed signal (VSS) (within vehicle speed window) and throttle position (TP) sensor (at part throttle) are required to enable the Catalyst Efficiency Monitor.

The DTCs associated with this test are DTC P0420 (Bank 1) and P0430 (Bank 2). Because an exponentially weighted moving average is used for malfunction determination, up to six driving cycles may be required to illuminate the MIL.

Comprehensive Component Monitor
The comprehensive component monitor (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 proper range of values. Where feasible, inputs are also checked for rationality, outputs are also checked for proper functionality.

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 performed 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 performed under appropriate test conditions.

Outputs such as the idle air control (IAC) solenoid 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 proper function by observing the reaction of the control system to a given change in the output command. An IAC solenoid can be functionally tested by monitoring idle rpm relative to the target idle rpm. Some tests can only be performed under appropriate test conditions; for example, 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.
- Inputs:
- Mass air flow (MAF) sensor
- Intake air temperature (IAT) sensor
- Engine coolant temperature (ECT) sensor
- Throttle position (TP) sensor
- Camshaft position (CMP) sensor
- Fuel tank pressure (FTP) sensor

- Outputs:
- Fuel pump (FP)
- Wide open throttle A/C cutout (WAC)
- Idle air control (IAC)
- Shift solenoid(s) (SS)
- Torque converter clutch (TCC) solenoid
- EVAP canister purge valve
- Canister vent (CV) solenoid

CCM is enabled after the engine starts and is running. A diagnostic trouble code (DTC) is stored in KAM and the MIL is illuminated after two driving cycles when a malfunction is detected. Manyof the CCM tests are also performed during the on demand self-test.

Evaporative Emission (EVAP) Vapor Management Flow System Monitor
The EVAP vapor management flow system monitor is designed to verify that the evaporative emission (EVAP) canister purge valve is functioning properly and to verify the flow of fuel vapor from the EVAP canister purge valve to the engine. The electrical function of the EVAP canister purge valve is initially checked before the flow test can begin. Inputs from the ECT sensor, IAT sensor, MAF sensor and VSS are used to enable the flow test.

NOTE: The EVAP vapor management flow test will not run if an EVAP canister purge valve malfunction is indicated. The DTC associated with an electrical fault of the EVAP canister purge valve is P0443 (EVAP system control valve circuit malfunction).

Before the flow test is performed, the PCM will calculate how much fuel vapor is present while purging under engine operation. If the amount of fuel vapor calculated is above a calibrated threshold, the PCM assumes that there must be fuel vapor flow to the engine and that the EVAP canister purge valve is functioning properly. If this condition exists, the idle speed portion of the EVAP vapor management flow test will be bypassed and the test will pass and complete.

If the amount of fuel vapor calculated is below a calibrated threshold, the idle speed portion of the EVAP vapor management flow test must be executed to verify that the EVAP canister purge valve is functioning properly. An assumption of the flow test is that regardless of the fuel vapor in the EVAP canister, some portion of the fuel vapor flow will be air. The flow test will calculate the increase in the idle air required by the PCM when the duty cycle on the EVAP canister purge valve is reduced from 75% to 0%.

If the calculated increase in airflow exceeds a calibrated threshold, the PCM assumes the EVAP canister purge valve is functioning properly. If the calculated increase in airflow is negligible, the EVAP canister purge valve is not functioning properly. The DTC associated with this condition is P1443 (EVAP control system purge control valve malfunction).
The MIL is activated for DTCs P0443 and P1443 after two occurrences of the same fault.

Evaporative Emission (EVAP) Running Loss System Monitor
The EVAP running loss system monitor is an on-board strategy designed to detect a leak from a hole (opening) equal to or greater than 1.016 mm (0.040 inch) in the EVAP running loss system. The proper function of the individual components of the EVAP running loss system as well as its ability to flow fuel vapor to the engine is also examined. The EVAP running loss system monitor relies on the individual components of the EVAP running loss system to apply vacuum to the fuel tank and then seal the entire EVAP running loss system from atmosphere. The fuel tank pressure is then monitored to determine the total vacuum lost (bleed-up) for a calibrated period of time. Inputs from the ECT sensor, IAT sensor, MAF sensor, VSS, FLI and FTP sensor are required to enable the EVAP running loss system monitor.

NOTE: During the EVAP running loss system monitor repair verification drive cycle, a PCM reset will bypass the minimum soak time required to complete the monitor. The EVAP running loss system monitor will not run if the key is turned off after a PCM reset. The EVAP running loss system monitor will not run if a MAF sensor failure is indicated. The EVAP running loss system monitor will not initiate until the heated oxygen sensor (HO2S) monitor has completed.

The EVAP running loss system monitor is executed by the individual components of the EVAP running loss system as follows:
1. The function of the EVAP canister purge valve is to create a vacuum on the fuel tank. A minimum duty cycle on the EVAP canister purge valve (75%) must be met before the EVAP running loss system monitor can begin.
2. The canister vent (CV) solenoid will close (100% duty cycle) with the EVAP canister purge valve at its minimum duty cycle to seal the EVAP running loss system from atmosphere and obtain a target vacuum on the fuel tank.
3. The FTP sensor will be used by the EVAP running loss system monitor to determine if the target vacuum on the fuel tank is being reached to perform the leak check. Once the target vacuum on the fuel tank is achieved, the change in fuel tank vacuum for a calibrated period of time will determine if a leak exists.
4. If the initial target vacuum cannot be reached, DTC P0455 (gross leak detected) will be set. The EVAP running loss system monitor will abort and not continue with the leak check portion of the test.
- If the initial target vacuum is exceeded, a system flow fault exists and DTC P1450 (unable to bleed-up fuel tank vacuum) is set. The EVAP running loss system monitor will abort and not continue with the leak check portion of the test.
- If the target vacuum is obtained on the fuel tank, the change in the fuel tank vacuum (bleed-up) will be calculated for a calibrated period of time. The calculated change in fuel tank vacuum will be compared to a calibrated threshold fora leak from a hole (opening) of 1.016 mm (0.040 inch) in the EVAP running loss system. If the calculated bleed-up is less than the calibrated threshold, the EVAP running loss system passes. If the calibrated bleed-up exceeds the calibrated threshold, the test will abort and rerun the test up to three times.
- If the bleed-up threshold is still being exceeded after three tests, a vapor generation check must be performed before DTC P0442 (small leak detected) will be set. This is accomplished by returning the EVAP running loss system to atmospheric pressure by closing the EVAP canister purge valve and opening the CV solenoid. Once the FTP sensor observes the fuel tank is at atmospheric pressure, the CV solenoid closes and seals the EVAP running loss system.
- The fuel tank pressure build-up for a calibrated period of time will be compared to a calibrated threshold for pressure build-up due to vapor generation.
- If the fuel tank pressure build-up exceeds the threshold, the leak test results are invalid due to vapor generation. The EVAP running loss system monitor will pass and complete.
- If the fuel tank pressure build-up does not exceed the threshold, the leak test results are valid and DTC P0442 will be set.

5. The MIL is activated for DTCs P0442, P0455 and P1450 (or P446) after two occurrences of the same fault. The MIL can also be activated for any EVAP running loss system component DTCs in the same manner. The EVAP running loss system component DTCs P0443, P0452, P0453 and P1451 are tested as part of the CCM.