Description

DTC 26 Air-Fuel Ratio Rich Malfunction

CIRCUIT DESCRIPTION
The main[1] oxygen sensor is located in the exhaust manifold. It indirectly determines whether the fuel mixture is rich or lean by detecting the concentration of oxygen present in the exhaust gas.

WIRING DIAGRAM




DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
DTC 25 - Type (1)
- (Main*1) oxygen sensor voltage is 0.45 volt or less (lean) for 90 sec. under conditions (a) and (b).
(2 trip detection logic)[2]
a. Engine coolant temperature : 60°C (140°F) or more.
b. Engine speed: 1,500 rpm or more.

TROUBLE AREA
- Open or short in (main*1) oxygen sensor circuit.
- Main[1] oxygen sensor
- Ignition system
- Engine control module

DTC 25 - Type (2)
- Engine speed varies by more than a predetermined rpm over the preceding crank angle period during a period of 20 sec. or more under conditions (a) and (b).
(2 trip detection logic)[2]
a. Engine speed: Idling
b. Engine coolant temperature : 60°C (140°F) or more.
TROUBLE AREA
- Open or short in injector circuit
- Fuel line pressure (injector leak, blockage)
- Mechanical system malfunction (skipping teeth of timing belt)
- Ignition system
- Compression pressure (foreign object caught in valve)
- Air leakage
- Engine control module

DTC 26
- Engine speed varies by more than a predetermined rpm over the preceding crank angle period during a period of 20 sec. or more under conditions (a) and (b).
(2 trip detection logic)[2]
a. Engine speed: Idling
b. Engine coolant temperature : 60°C (140°F) or more.

TROUBLE AREA
- Open or short in injector circuit
- Fuel line pressure (injector leak, blockage)
- Mechanical system malfunction (skipping teeth of timing belt)
- Ignition system
- Compression pressure (foreign object caught in valve)
- Air leakage
- Engine control module

[1] "Main" is for Ca. specification vehicles only. All others have only 1 oxygen sensor.
[2] Refer to Description of 2 Trip Detection Logic under Trouble Code Descriptions

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 oxygen sensor
Open or short in injector circuit, injector leak or blockage.
HINT: Before this test, check the feedback voltage for oxygen sensor.

Driving Detection Pattern For DTC 25 / 26:

(1) Disconnect the EFI fuse (15 A) for 10 sec. or more, with IG switch OFF. Initiate test mode (Connect terminal TE2 and E1 of data link connector 1 with IG switch OFF).
(2) Start engine and warm up.
(3) After the engine is warmed up, let it race at 2,500 rpm for 3 min.
(4) After performing the racing in (3), perform idling for 1 min.

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.