Description
DATA TROUBLE CODE: 21SYSTEM: Main Heated Oxygen Sensor Circuit
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
- Open or short in heater circuit of main heated oxygen sensor for 0.5 seconds or more.
OR
- Main heated oxygen sensor signal voltage is reduced to between 0.35 volts and 0.70 volts for 60 seconds under the followinhg conditions:
- Engine coolant temperature Between 70°C and 95°C (203°F)
- Engine speed 1,500 rpm or more.
- Load driving (EX. A/T in 4th speed, A/C ON, Flat road, 80km/h (50 mph)).
- Main heated oxygen sensor signal voltage alternating above and below 0.45 volts.
TROUBLE AREA
- Open or short in heater circuit of main heated oxygen sensor.
- Main heated oxygen sensor heater.
- engine control module
OR
- Main heated oxygen sensor circuit.
- Main heated oxygen sensor
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.
Driving Pattern
It is vital that this test routine is adhered to detect the malfunction:
1. Disconnect the EFI fuse (30 A) 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 the engine and warm up with all ACC switch OFF.
3. After the engine is warmed up, let it idle for 3 minutes.
4. After performing the idling in 3, perform gradual acceleration within the range 1,300 to 1,700 rpm (centered around 1,500 rpm) with the A/C switch ON and D position for A/T (5th for M/T).
HINT: Ensure engine rpm does NOT fall below 1200 rpm. Gradually depress the accelerator pedal at a suitable rate to comply with the test requirements on the above graph. Never allow engine rpm to drop at any time during the test.
5. Maintain the vehicle speed at 40 - 50 mph.
6. Keep the vehicle running for 1 - 2 minutes after starting acceleration.
NOTE: If a malfunction exists, the Malfunction Indicator Lamp will light up after approximately 60 seconds from the start of acceleration. If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
HINT: Diagnostic trouble code 21 is for the left bank main heated oxygen sensor circuit. Diagnostic trouble code 28 is for the right bank main heated oxygen sensor circuit.
Malfunction Indicator Lamp
Normal Mode On
Test Mode On