General Description
In order to provide the best possible combination of drivability, fuel economy and emission control, the ECM uses a closed loop air/fuel metering system. The ECM monitors the HO2S signal voltage and adjusts fuel delivery based it in closed loop fuel control. Changes in fuel delivery will be indicated by the long-term and the short-term fuel trim values. The ideal fuel trim value is around 0%. The ECM will add fuel when the HO2S signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0%. The ECM will reduce fuel when 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 amount reaches excessive levels because of a lean or rich condition.
DTC Description
Breaking the lambda adaptation and lambda controller limits for a long time, which may have been caused by failures in the fuel or intake system will involve emission rise and therefore shall be diagnosed by fuel system monitoring. The lambda controller deviation including adaptive terms are used for fuel system monitoring. The time counter is increased if lambda controller exceeds the threshold and the ECM sets DTC P0171 or P0172 respectively depending on direction of lambda controller deviation. P0171 is set with positive deviation and P0172 is set with negative deviation. If same error code is set in the next driving cycle, the ECM illuminates the MIL.
DTC Detecting Condition
Item | Detecting Condition | Possible cause |
Monitoring Strategy | ? Mixture adaptation value check low | ? Faulty ignition system. ? EVAP PCSV malfunction. ? Faulty fuel injectors. ? Leak in exhaust system. ? Faulty MAP,TPS,ECTS. ? Faulty front HO2S. |
Case1 | Threshold value | ? Additive long term value : < -10% |
Enable Conditions | ? Engine speed = 920rpm ? Air mass = 24kg/h |
Diagnostic Time | ? 30 sec |
Case2 | Threshold value | ? Multiplicative long term value of the higher load < 0.77 |
Enable Conditions | ? Engine load = 70% ? Air mass = 100kg/h |
Diagnostic Time | ? 25 sec |
Case3 | Threshold value | ? Multiplicative long term value of the lower load > 0.77 |
Enable Conditions | ? Engine load 30 ~ 55% ? Air mass 40 ~ 80kg/h |
Diagnostic Time | ? 25 sec |
Fail Safe | ? None |
Specification
Fuel Trim | Normal Parameter |
2500 rpm | When engine is suddenly raced |
Control | Closed loop | Open loop |
Signal Waveform
This figures show the waveform measured at terminal 2 of HO2S at idle.
The average voltage of HO2S should be 0.5 V.
The HO2S voltage at point ? is lean air/fuel duration and its usual voltage is below 0.2V.
The HO2S voltage at point ? is rich air/fuel duration and its usual voltage is over 0.7V.
In case the duration ? is longer than the duration ?
Possible cause : Clloged injector,low fuel pressure faulty MAPS, air leakage in intake system. |
In case the duration ? is longer than the duration ?
Possible cause : Injector leakage,high fuel pressure,faulty MAP sensor faulty ECTS. |