Component Location
General Description
The rear heated oxygen sensor is mounted on the rear side of the Catalytic Converter (warm-up catalytic converter) or in the rear exhaust pipe, which is able to detect catalyst efficiency. The rear heated oxygen sensor (HO2S) produces a voltage between 0V and 1V. This rear heated oxygen sensor is used to estimate the oxygen storage capability. If a catalyst has good conversion properties, the oxygen fluctuations are smoothed by the oxygen storage capacity of the catalyst. If the conversion provided by the catalyst is low due to aging, poisoning or misfiring, then the oxygen fluctuations are similar to signals from the front oxygen sensor.
DTC Description
Checking output signals from HO2S during deceleration fuel cut-off, if the HO2S's response time is too long, ECM sets P2A01. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycles.
DTC Detecting Condition
Item | Detecting Condition | Possible cause |
DTC Strategy | Monitor HO2S's response
| Poor connection Faulty HO2S Faulty ECM |
Enable Conditions | After engine warming-up
Deceleration fuel cut-off state
No other disabling faults
|
Threshold value | The average time for voltage drop > approx. 0.3 seconds
|
Diagnosis Time | During deceleration fuel cut-off
|
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.