In order to provide the best possible combination of drivability, fuel economy, and emission control, the ECM uses aclosed loop air/fuel metering system. The ECM monitiors the HO2S signal voltage and adjusts the fuel delivery basedon the HO2S signal voltage in closed loop fuel control. Changes in fuel delivery will be indicated by the short-term andthe long-term fuel trim values. The ideal fuel trimvalue is around 0%. The ECMwill add fuel when the HO2S signal isindicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0%. The ECM will reduce fuelwhen the HO2S signal is indicating a rich condition. Reduction in fuel is indicated by fuel trim values that are below 0%.The DTC relevant to fuel trim will be set when the value reaches excessive levels because of a lean or rich condition.
The ECM monitors the trim of lambda control by the rear HO2S signal in addition to the HO2S monitoring. The trim value calculation is based on the difference of rear HO2S signal from desired value. The ECM sets DTC P2096 if either trim value or the difference of rear HO2S from desired value is reached to the maximum threshold.If the same error code is set in the next driving cycle, the ECM illuminates the MIL.
Item
Detecting Condition
Possible Cause
DTC Strategy
Signal check,High
Contact resistance in connections.
Exhaust System
Faulty Catalytic converter
Faulty HO2S(UP)
Enable Conditions
Dew point end detected
Target lambda = 1
Battery voltage > 10.7V
Exhaust gas temperature (model) : 600? ~ 800?
No upstream O2 sensor error or downstream O2 sensor ready
1800 rpm < Engine speed < 3400 rpm
Engine load : 22.5~65.3%
Threshold Value
Second lambda controller from downstream lambda control > 1.2 s
Diagnostic Time
20 sec
MIL ON Condition
3 driving cycle
Temperature
Frone HO2S Heater Resistance
20 ?
9.0 ?
The amplitude of the signal output of the rear HO2S is small compared to the front HO2S because the rear HO2S detects emission gas purified by the catalytic converter. This is the normal signal waveform of the rear HO2S at idle.