Component Location
General Description
In order to control emissions of the CO, HC and NOx components of the exhaust gas, heated oxygen sensor (HO2S), mounted on the front side and rear side of catalytic converter, detects the oxygen content in the exhaust gas. The front HO2S signal is used to control air/fuel ratio (closed loop fuel control) and the rear HO2S signal is used to monitor front HO2S and catalyst for proper operation. The HO2S requires a minimum temperature to operate properly and provide a closed loop fuel control system. The HO2S contains the heater element to reduce its warming-up time and ensure its performance during all driving conditions. The oxygen sensor generates a voltage that indicates the difference between the oxygen content of the exhaust stream and the oxygen content of ambient air. When the exhaust stream is “rich,” there is more oxygen in the ambient air than in the exhaust stream, so the voltage will be higher.
DTC Description
Checking output signals from HO2S under detecting condition, if HO2S is not ready, ECM sets P2A03.
DTC Detecting Condition
Item | Detecting Condition | Possible cause |
DTC Strategy | Monitor HO2S status
| Poor connection Faulty HO2S Faulty ECM |
Enable Conditions | Engine Running at idle > 20 sec.
|
Threshold value | HO2S is not ready
|
Diagnosis Time | Continuous (More than 10 second failure for every 12 second test .)
|
MIL On Condition | 2 Drive Cycle
|
Specification
A/F Ratio (?) | Output Voltage (V) |
RICH | Min. 0.8 |
LEAN | Max. 0.1 |
Diagnostic Circuit Diagram
Signal Waveform & Data
Fig 1) Normal waveforms of upstream HO2S(the upper) and downstream HO2S(the lower) (chassis ground used)
Fig 2) Normal waveforms of upstream HO2S(the upper) and downstream HO2S(the lower) (sensor ground used)
Fig 3) Normal graph of upstream HO2S and downstream HO2S at idle.
When at operating temperature, if accelerator pedal is released suddenly, around 4000 rpm, the HO2S signal reading will be lower than 200 mV, resulting from Fuel cut-off for the moment. Conversely, with sudden accelerator pedal depress, HO2S signal reading will be around 0.6V ~1.0V. At idle, HO2S signal will switch from lean to rich at 3 Hz, on acceleration, its frequency increases.