DTC 26
DTC 26 Air-Fuel Ratio Rich Malfunction
Oxygen Sensor Cut-Away:
Oxygen Sensor Output Voltage Chart:
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HO 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 ECM of the LEAN condition (small electromotive force: 0 V).
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 ECM of the RICH condition (large electromotive force: 1 V).
The ECM judges by the electromotive force from the oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection duration accordingly. However, if malfunction of the oxygen sensor causes an output of abnormal electromotive force, the ECM 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 ECM. 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.)
DETECTING CONDITION
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diagnostic trouble code detecting condition after diagnostic trouble code is recorded.
(b) To check that the malfunction is corrected when the repair is completed confirming that diagnostic trouble code is no longer detected.
Malfunction: Open or Short in Main Heated Oxygen Sensor
Detection Driving Pattern Step 1:
HINT: Before this test, check the feedback voltage for oxygen sensor.
(1) Disconnect the EFI No.1 fuse (30A) for 10 sec. or more with IG switch OFF. Initiate test mode (Connect terminal TE2 and E1 of data link connector 2 with IG switch OFF).
(2) Start engine and warm up.
(3) Idle the engine for 3 min.
(4) Race the engine quickly to 4,000 rpm 3 times using the accelerator pedal.
(5) Race the engine at 2,000 rpm for 90 sec.
HINT: If a malfunction exists, the malfunction indicator lamp will light up during step (4).
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
DIAGNOSTIC TROUBLE CODE DETECTION DRIVING PATTERN
Purpose of the driving pattern.
(a) To simulate diagnostic trouble code detecting condition after diagnostic trouble code is recorded.
(b) To check that the malfunction is corrected when the repair is completed confirming that diagnostic trouble code is no longer detected.
Detection Driving Pattern Step 2:
Malfunction: Open or Short in Injector circuit, Injector Leak or Blockage
(1) Disconnect the EFI No.1 fuse (30A) for 10 sec. or more with IG switch OFF.
Initiate test mode (Connect terminal TE2 and E1 of data link connector 2 with IG switch OFF).
(2) Start engine and warm up with all ACC switched OFF.
(3) Idle the engine for 5 min. (After the engine is started, do not depress the accelerator pedal.)
HINT: If a malfunction exists, the malfunction indicator lamp will light up during the 5 min. idling period.
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
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INSPECTION PROCEDURE