Component Location
General Description
The HO2S is used to supply the ECM with information regarding the composition of the air/fuel mixture. The HO2S is positioned in the exhaust pipe ahead of the TWC. To measure the oxygen content, the HO2S requires a supply of ambient air as a reference. Since this is supplied through the wiring, the lead must not be clamped or damaged in any other way. The HO2S produces a voltage that varies between 0.1V and 0.9V under normal operating conditions. The Engine Control Module (ECM) monitors this voltage and determines if the exhaust gas is lean or rich. If the voltage input at the ECM is under approx. 0.45V the exhaust is lean, and if the voltage input is over approx. 0.45V the exhaust is rich. The ECM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary.
DTC Description
Due to possible oxygen sensor defects or faults in the injection system (e.g. leaking fuel injector), the front or rear oxygen sensor may not provide the expected lean or rich signal level during fuel cut-off or full load condition. Hence, the oxygen sensor.If ECM detects no signal changes in Heated Oxygen Sensor DTC P0134 or P0140 sets
DTC Detecting Condition
Item | Detecting Condition | Possible cause |
Monitoring Strategy | ? Signal check, wiring interruption | ? Open in signal and ground circuit ? Short to battery in control circuit ? Faulty HO2S ? Faulty ECM ? Poor connections between HO2S and ECM ? Misplaced,bent,loose or corroded terminals. |
Case1 | Threshold value | ? Sensor voltage : > 0.2V |
Enable Conditions | ? During fuel cut-off ? Downstream O2 sensor voltage > 0.2V |
Diagnostic Time | ? 3 sec |
Case2 | Threshold value | ? Sensor voltage : > 0.2V |
Enable Conditions | |
Diagnostic Time | ? 5 sec |
Case3 | Threshold value | ? Internal resistance > 20k? |
Enable Conditions | ? Exhaust gas temperature > 600?(1112?) |
Diagnostic Time | |
Fail Safe | ? None |
Specification
HO2S | Normal Parameter(at 1300 rpm after warming up) |
Rich | Lean |
Signal Voltage | 0.6 ~ 1.0 V | 0 ~ 0.4 V |
Hi-scan Data display | Engine condition |
When deceleration suddenly from 4000rpm | 200 mV or lower |
When engine is suddenly raced | 600 ~ 1000 mV |
Schematic Diagram
Signal Waveform
This figures show the wave form measured at terminal 2 of HO2S at idle RPM.
The average voltage of HO2S should be 0.5 V.
When sudden decceleration,the voltage at point ? should be below 0.2V.
The switching time marked ? from lean to rich should be within 200ms,if longer than 200ms HO2S may be not good.
The switching time marked ? from rich to lean should be within 300ms,if longer than 300ms HO2S may be not good.
In case the average voltage of HO2S is over 0.6V.
Possible cause:Injector leakage,faulty Pressure regurator Faulty MAPS,ECTS. |
The rear oxygen sensor output is usually not changeable like front oxygen sensor,however,if it moves like front oxygen sensor,the catalytic converter is broken.