Mazda CX-9 2007 Service Highlights page 29

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.
ON-BOARD DIAGNOSTIC [MZI-3.5]
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