DTC 25
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 increase 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 time accordingly. However, if malfunction of the oxygen sensor causes output of abnormal electromotive force, the ECM is unable to perform accurate air-fuel ratio control.
DETECTING CONDITION AND TROUBLE AREA
*1: Only for California specification vehicles
*2: This indicates items for which "2 trip detection logic" is used. With this logic, when a logic malfunction is first detected, the malfunction is temporarily stored in the ECM memory. If the same case is detected again during the second drive test, this second detection causes the Malfunction Indicator Lamp to light up.
The 2 trip repeats the same mode a 2nd time. (However, the IG switch must be turned OFF between the 1st trip and 2nd trip).
In the Test Mode, the Malfunction Indicator Lamp lights up the 1st trip a malfunction is detected.
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.
Malfunction: Open or Short in (Main Heated*) Oxygen Sensor.
HINT: Before this test, check feedback voltage for oxygen sensor.
1. Remove EFI fuse (30 A) for 10 seconds or more, with ignition switched OFF. Initiate test mode (Connect terminal TE2 and E1 of data link connector 2 with ignition switched OFF).
2. Start engine and warm up.
3. Let engine idle for 3 minutes.
4. Quickly race engine to 4,000 rpm 3 times.
5. Race engine at 2,000 rpm for 90 seconds.
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.
*: Only for California specification vehicles.
Malfunction: Open or Short in Injector Circuit, Injector Leak or Blockage.
HINT: Before this test, check feedback voltage for oxygen sensor.
1. Remove EFI fuse (30 A) for 10 seconds or more, with ignition switched OFF. Initiate test mode (Connect terminal TE2 and E1 of data link connector 2 with IG switched OFF).
2. Start engine and warm up with all accessories switched OFF.
3. Let engine idle for 5 minutes. (After engine is started, do not depress accelerator pedal.)
4. If malfunction is not detected during idling, race engine without any load at approx. 2,000 rpm for 60 seconds
HINT: If a malfunction exists, the malfunction Indicator lamp will light up during the 5 minutes idling period or within 60 seconds of starting racing.
NOTICE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
DIAGNOSTIC CHART
WIRING DIAGRAM
INSPECTION PROCEDURE