On-Board Diagnostic System Malfunction Detection Function[Mzi-3.5]; Features; Malfunction Diagnosis Function - Mazda CX-9 2007 Service Highlights

ON-BOARD DIAGNOSTIC SYSTEM MALFUNCTION DETECTION FUNCTION[MZI-3.5]

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.
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ON-BOARD DIAGNOSTIC [MZI-3.5]
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