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
ECM set P2272 code if output signal is too low at DOWN O2 sensor when AIR-FUEL ratio is under thick condition.
DTC Detecting Condition
Item | Detecting Condition | Possible cause |
DTC Strategy | No signal activity
| Poor connection Open or Short to ground in harness HO2S(B2/S2) ECM |
Enable Conditions | Battery voltage > 10.7V
Lambda = 0.9 for 9 sec
|
Threshold value | Downstream O2S voltage < 0.65V
|
Diagnosis Time | 9 sec
|
MIL On Condition | 2 Driving Cycles
|
Diagnostic Circuit Diagram
Signal Waveform & Data
Fig. 1) Normal waveforms of front HO2S(the upper) and rear HO2S(the lower)
After warming-up, if accelerator pedal is released suddenly around 4000rpm, the HO2S signal reading will be lower than 200mV resulting from Fuel cut-off for the moment. Conversely, if suddenly accelerator pedal is depressed, HO2S signal reading will be around 0.6V ~1.0V. At idle, Normally HO2S signal will switch from lean to rich with 3 Hz. And as racing, Its frequency rises.