Description
DATA TROUBLE CODE: 25SYSTEM: Air-Fuel Ratio Lean Malfunction
CIRCUIT DESCRIPTION
To obtain a high purification rate for the Co, HC and NOx components of the exhaust gas, a three-way catalytic converter is used, but for most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio.
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust gas and provide feedback to the computer for control of the air-fuel ratio.
When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sensor informs the engine control module of the LEAN condition (small electromotive force: 0 Volt).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio the oxygen concentration in the exhaust gas is reduced and the oxygen sensor informs the engine control module of the RICH condition (large electromotive force: 1 Volt).
The engine control module judges by the electromotive force from the oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes output of abnormal electromotive force, the engine control module is unable to perform accurate air-fuel ratio control.
The main heated oxygen sensors include a heater which heats the Zirconia element. The heater is controlled by the engine control module. When the intake air volume is low (the temperature of the exhaust gas is low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.
DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
- Main heated oxygen sensor voltage is 0.45 volts or less (lean) for 90 seconds under the following conditions: (2 trip detection logic)
- Engine coolant temperature 60°C (140°F) or more.
- Engine speed 1,500 rpm or more.
OR
- Main heated oxygen sensor voltage is alternating above and below 0.45 volts at 5 times per second or more under the following conditions: (2 trip detection logic)
- Engine speed Idling.
- Engine coolant temperature between 60°C (140°F) and 95°C (203°F).
OR
- Difference of air-fuel ratio feedback compensation value between right and left banks is more than 10 percentage for 30 seconds or more under the following conditions: (2 trip detection logic)
- Engine speed 2,000 rpm or more.
- Engine coolant temperature between 60°C (140°F) and 95°C (203°F).
TROUBLE AREA
- Open or short in main heated oxygen sensor circuit.
- Main heated oxygen sensor.
- Ignition system.
- Engine coolant temperature sensor.
OR
- Open or short in injector circuit.
- Fuel line pressure (injector blockage).
- Volume air flow meter (Air intake).
- Engine ground bolt loose.
- Foreign object caught in valve.
OR
- Fuel line pressure (injector leak, blockage).
- Mechanical system malfunction (skipping teeth of timing belt).
- Ignition system.
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern
To simulate Diagnostic Trouble Code detecting condition after Diagnostic Trouble Code is recorded. To check that the malfunction is corrected when the repair is completed confirming that Diagnostic Trouble Code is no longer detected.
Detection Driving Pattern - Open or Short in Main Oxygen Sensor
NOTE: Before this test, check the feedback voltage for Oxygen Sensor.
1. Disconnect the EFI fuse (30A) for 10 seconds or more with Ignition switch OFF.
Initiate test mode (Connect terminal TE2 and E1 of Data Link Connector 1 or 2 with Ignition switch OFF).
2. Start engine and warm up.
3. After engine is warmed up, let it idle for 3 minures.
4. Perform quick racing to 4,000 rpm 3 times by accelerator pedal.
5. After performing the racing in 4, perform racing at 2,000 rpm for 90 seconds. If a malfunction exists, the Malfunction Indicator Lamp will light up during step 4.
NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible. If a malfunction exists, the Malfunction Indicator Lamp will light up during step 4.
Detection Driving Pattern - Open or Short in Injector Circuit, Injector Leak or Blockage
1. Disconnect the EFI fuse (30 A) for 10 seconds or more with Igintion switch OFF. Initiate test mode (Connect terminal TE2 and E1 of Data Link Connector 1 or 2 with Ignition switch OFF).
2. Start engine and warm up with all ACC switch OFF.
3. After engine is warmed up, let it idle for 5 minutes. After the engine is started, do not depress the accelerator pedal.
4. If the malfunction is not detected during idling, perform racing without any load at approximately 2,000 rpm for 60 seconds.
NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible. If a malfunction exists, the malfunction indicator lamp will light up during the 5 min. idling period or within 60 seconds of starting racing.
Malfunction Indicator Lamp
Normal Mode On
Test Mode On