Mazda CX-9 Grand Touring 2009 Manual page 853

Engine speed (PID: RPM)
Rear HO2S voltage (PID: O2S12, O2S22)
3. Drive the vehicle and decelerate the engine speed by releasing the accelerator pedal fully when the engine
speed is 3,000 rpm or more.
4. Verify that the rear HO2S outputs a voltage of 0.6 V or more , one time or more, then verify that the rear
HO2S voltage (PID: O2S12, O2S22) is 0.3 V is or less while decelerating as shown in the figure.
Fig. 32: Output Voltage Graph
Courtesy of MAZDA MOTORS CORP.
If not within the specification, inspect the rear HO2S for an open or short circuit. Then if there is no
malfunction in the wiring harness, replace the rear HO2S. (See REAR HEATED OXYGEN
SENSOR (HO2S) REMOVAL/INSTALLATION [MZI-3.7].)
HO2S HEATER RESISTANCE INSPECTION
1. Disconnect the HO2S connector.
2. Measure the resistance between HO2S terminals C and A.
If it is not within the specification, replace the HO2S. (See REAR HEATED OXYGEN SENSOR
(HO2S) REMOVAL/INSTALLATION [MZI-3.7].)
If the monitor item status/specification (reference) is not within the specification, even though the
resistance is within the specification, perform the "Circuit Open/Short Inspection".
HO2S heater resistance
2008 Mazda CX-9 Grand Touring
2008 ENGINE Control System (MZI-3.7) - Mazda CX-9