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 an output signal is below 0.04V for more than predeterminate time, ECM sets P0151. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | Monitor signal voltage
| Poor connection
Short to ground in harness
HO2S(B2/S1)
ECM
|
Enable Conditions | Battery voltage = 10V
Engine running = 60 sec
Engine warm-up state
|
Threshold value | The voltage of HO2S(B2/S1) < 0.04V
|
Diagnosis Time | Continuous (more than 12.5 sec. failure for every 15 sec.test)
|
MIL On Condition | 2 Driving Cycles
|
Specification
(Reference only)Test Condition | HO2S Voltage(Sensor1) | HO2S Voltage(Sensor2) |
HO2S Signal at idle after warm-up | Signal is commonly switching from rich to lean more than 3 times in 10 sec. | Signal is commonly above 0.6V. |
HO2S signal at open circuit (Pumping current OFF) | Approx. 0.45V |
HO2S signal at open circuit (Pumping current ON) | Approx.2.2V |
Diagnostic Circuit Diagram
Signal Waveform & Data
Fig.1) Normal waveforms of front HO2S(the upper) and rear HO2S(the lower). (Waveform between HIGH signal line of HO2S and chassis ground)
Fig.2) Normal graph of front HO2S and rear HO2S at idle.
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.