ON-BOARD DIAGNOSTIC SYSTEM MALFUNCTION DETECTION FUNCTION [MZI-3.7]

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Features

• If any malfunction develops in the engine control system, the PCM stores that malfunction as a DTC. Stored DTCs can be read-out using the Mazda Modular Diagnostic System (M-MDS).
• The malfunction detection function includes malfunction diagnosis and self-test functions.

Malfunction Diagnosis Function

• This function detects malfunctions that develop in the engine control system.
• When the malfunction conditions are consistent with the malfunction determination conditions preset in the PCM, the PCM determines that an engine control system malfunction has occurred and stores the corresponding DTC (s).

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 effect emissions and is not monitored by another system monitor. Inputs and outputs are, at a minimum, monitored for circuit continuity or specified range of values. Where feasible, inputs are also inspected for rationality, and outputs are inspected 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 inspected continuously for opens, shorts, and unspecified values. Some digital inputs such as brake switch on rationality inspection; inspecting if the input value makes sense at the current engine operating conditions. These types of tests require monitoring several components and can only be performed under appropriate test conditions.
  • Outputs such as coil drivers are checked for open and short circuits by monitoring a feedback circuit or “dedicated IC chip” 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. Some tests can only be carried out under appropriate test conditions.
  • The following is an example of some of the input and output components monitored by the CCM for OBD. The monitored components belong to a PCM supported subsystem.
  Inputs
    ― Includes: CHT sensor, IAT sensor, MAF sensor, TP sensor, CKP sensor, CMP sensor, Fuel tank pressure sensor, refrigerant pressure switch (medium pressure)
  Outputs
    ― Includes: Fuel pump, A/C relay, purge solenoid valve, CV solenoid valve, OCV
  • The CCM is activated after the engine is started and is operating. A DTC is stored in the PCM memory and the MIL is illuminated if a malfunction is detected for two consecutive drive cycles. Many of the CCM monitor items are also performed during self-test.

Fuel System Monitor

  • The fuel system monitor is an on-board function designed to monitor correction values for fuel injection control. The fuel control system uses fuel injection learning correction values stored in the PCM to compensate for deviations in fuel system components due to normal wear and aging. During fuel system feedback control, fuel injection control learns the corrections required to correct a “biased” rich or lean fuel system. These corrections are stored as fuel feedback correction coefficients. Fuel injection control has two correction methods: Long term and short term fuel corrections. Long term fuel correction uses the learning correction coefficient and short term fuel correction uses the fuel feedback correction coefficient. Inputs from the CHT, IAT, and MAF sensors are required to activate fuel injection control and perform fuel system monitor. Once activated, the fuel system monitor inspects if the fuel feedback and fuel learning correction coefficients exceed a specified limit. When a malfunction is detected as described below, the fuel system monitor stores a corresponding DTC.
    ― The HO2S detects the presence of oxygen in the exhaust gas and provides the PCM with feedback indicating the air/fuel ratio.
    ― A correction factor is added to the fuel injector pulse width calculation according to the long and short term fuel corrections as needed to compensate for deviations in the fuel system.
    ― As the deviation from the stoichiometric air/fuel ratio becomes larger, air/fuel ratio control suffers and uncombusted gas in the exhaust increase. If the stoichiometric air/fuel ratio exceeds the specified limit and the fuel correction coefficient approaches the specified limit, the fuel system monitor stores DTCs as follows:
      • DTCs P0171 and P0174: Detection of a lean shift in fuel system operation
      • DTCs P0172 and P0175: Detection of a rich shift in fuel system operation
  • The MIL is illuminated if a malfunction is detected during two consecutive drive cycles.

HO2S Monitor

  • The HO2S monitor is an on-board diagnostic function designed to monitor the HO2S for malfunctions or deterioration that can affect emissions. The HO2S used for fuel injector control is monitored for proper output voltage. Inputs from the CHT, IAT, MAF and CKP sensors are required for HO2S monitor operation. The fuel system and misfire detection monitors must also have been performed successfully before the HO2S monitor is activated.
    ― The HO2S detects the oxygen content in the exhaust gas and outputs voltage between 0—1.0 V. If the air fuel ratio is leaner than the stoichiometric air/fuel ratio (14.7: 1), the HO2S generates 0—0.45 V. If the air fuel ratio is richer than the stoichiometric air/fuel ratio (14.7: 1), the HO2S generates 0.45—1.0 V. The HO2S monitor evaluates the HO2S for proper operation.
    ― The time between HO2S switches is monitored after the engine is started and during fuel system feedback conditions. Excessive time between switches or no switches since engine startup indicates a concern. Since a lack of switching can be caused by HO2S concerns or by shifts in the fuel system, DTCs are stored that provide additional information for this concern. Different DTCs indicate whether the sensor always indicates lean/disconnected (P2195 or P2197), or always indicates rich (P2196 or P2198). The HO2S signal is also monitored for high voltage, in excess of 1.1 V and stores a unique DTC (P0132 or P0152). An excess voltage condition is caused by a HO2S heater or battery power short to the HO2S signal line.
    ― A functional test of the rear HO2S is done during normal vehicle operation. The peak rich and lean voltages are continuously monitored. Voltages that exceed the calibrated rich and lean thresholds indicate a functional sensor. If the voltages have not exceeded the thresholds after a long period of vehicle operation, the air/fuel ratio may be forced rich or lean in an attempt to get the rear sensor to switch. If the sensor does not exceed the rich and lean peak thresholds, a concern is indicated. The HO2S signal is also monitored for high voltage, in excess of 1.1 V and stores a unique DTC (P0138 or P0158). An excess voltage condition is caused by a HO2S heater or battery power short to the HO2S signal line.
    ― The HO2S monitor DTCs can be categorized as follows:
      • P0040, P0041: Property failure
      • P0133, P0139, P0153, P0159: Slow response rate
      • P0053, P0054, P059, P0060: Heater circuit malfunction
      • P1127: Rear HO2S not running in on-demand self-test
      • P2195, P2196, P2197, P2198: HO2S lack of switching
      • P2270, P2272: HO2S lack of switching (sensor indicates lean)
      • P2271, P2273: HO2S lack of switching (sensor indicates rich)
  • The MIL is illuminated if a malfunction is detected during two consecutive drive cycles.

Misfire Detection Monitor

  • The misfire detection monitor is an on-board diagnostic function designed to detect engine misfire and identify in which cylinder the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The misfire detection monitor will only be enable when certain base engine conditions are first satisfied. Inputs from the CHT, IAT, MAF and CKP sensors are required for the monitor to be performed. The misfire detection monitor is also activated during the self-test.
    ― The PCM synchronizes the ignition timing with crankshaft rotation signal from the CKP sensor. The crankshaft rotation signal is also the main signal used for determining which cylinder misfires.
    ― The crankshaft rotation signal generated by the CKP sensor is derived from by sensing the passage of teeth on the crankshaft position wheel mounted on the end of the crankshaft.
    ― This signal is input to the PCM and then used to calculate the time between crankshaft rotation signals, and also crankshaft rotation speed and acceleration. The power loss of each cylinder is determined by comparing the accelerations of each cylinder. When the power loss of a particular cylinder exceeds a specified value and other conditions are met, then that cylinder is determined to have misfired.
    Misfire type A
      • Upon detection of a serious misfire that could cause catalyst damage, the MIL flashes once per second during the misfire and a DTC is stored.
    Misfire type B
      • Upon detection of a misfire that could exceed the emission limits or cause the vehicle to fail an inspection and maintenance tailpipe emissions test, the MIL illuminates and a DTC is stored. DTC P0300 is stored in the case of a multiple cylinder misfire.
    ― DTCs P0301, P0302, P0303, P0304, P0305, and P0306 are stored in case of an individual type A or type B single cylinder misfire.
    ― DTC P0316 is stored if a type B threshold is exceeded during the first 1,000 revolutions after engine startup. This DTC is stored in addition to the normal P03xx DTC that indicates the misfiring cylinder.

Catalyst Efficiency Monitor

  • The catalyst efficiency monitor uses an oxygen sensor before and after the catalyst to infer the 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 fuel system feed back control conditions, high efficiency catalysts have significant oxygen storage. This makes the switching frequency of the rear 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 rear HO2S signal begins to switch more rapidly with increasing amplitude and signal length, approaching the switching frequency, amplitude, and signal length of the front HO2S. The predominant failure mode for high-mileage catalysts is chemical deterioration (phosphorus deposits on the front brick of the catalyst), not thermal deterioration.
  • Inputs from CHT, IAT, MAF, TP, CKP and vehicle speed sensors are required to enable the catalyst efficiency monitor.
  • The DTCs associated with this test are DTC P0420 and P0430.
  Because an exponentially weighted moving average algorithm is used to determine a concern, up to 6 driving cycles may be required to illuminate the MIL during normal customer driving. If the PCM memory is reset or the battery is disconnected, a concern illuminates the MIL in 2 drive cycles.

Thermostat Monitor

  • The thermostat monitor is designed to verify correct thermostat operation. This monitor is executed once per drive cycle and has a monitor run duration of 300—800 s. If a concern is present, P0128 is set and the MIL is illuminated.
  • The monitor inspections the CHT sensor to warm up in a predictable manner when the engine is generating sufficient heat. A timer is initialized while the engine is at moderate load and the vehicle speed is above a calibrated limit. The target timer value is based on ambient air temperature at engine start-up. If the timer exceeds the target time and CHT has not warmed up to the target temperature, a concern is indicated.
  • The test runs if the start-up intake air temperature is at, or below the target temperature.
  Inputs
    ― Includes: CHT, IAT, engine LOAD (from MAF sensor), vehicle speed input

On-board Diagnostic System (OBD) Readiness Test

  • Allows verification of whether or not the OBD items (monitor items) set in the PCM have been successfully completed.
  • Fuel injection control, and CCM and non-CCM components, are constantly monitored since their status is constantly diagnosed.
  • The status of intermittently monitored diagnostic items can be initiated by activating the initialization function for diagnostic data.

Self-test Function

• The self-test function consists of the KOEO (Key On, Engine Off) self-test, performed when the ignition switch is turned to the ON position and the engine is stopped, and the KOER (Key On, Engine Running) self-test, performed when idling.
• When the self-test is activated, the PCM performs engine control system diagnosis. If any malfunction is detected as a result of the diagnosis, the applicable DTC is stored. Stored DTCs can be read-out using the Mazda Modular Diagnostic System (M-MDS).
• Using the self-test function, the present malfunction or a successful repair is readily confirmed. Refer to the self-test table for the corresponding DTCs.

KOEO (Key ON, Engine Off) Self-test

  • The KOEO self-test, performed when the ignition switch is turned to the ON position and the engine is stopped, is designed to diagnose malfunctions related to DTCs applicable to this self-test function. A KOEO self-test begins when the connected the Mazda Modular Diagnostic System (M-MDS) sends an execute command to the PCM.

KOER (Key ON, Engine Running) Self-test

  • The KOER, self-test performed when the ignition switch is turned to the ON position, the vehicle is stopped and the engine is idling, is designed to diagnose malfunctions related to DTCs applicable to this self-test function. A KOER self-test begins when the connected the Mazda Modular Diagnostic System (M-MDS) an execute command to the PCM.