25 Air–Fuel Ratio Lean Malfunction
26 Air–Fuel Ratio Rich Malfunction
CIRCUIT DESCRIPTION
The main oxygen sensor is located in the exhaust manifold.
It indirectly determines whether the fuel mixture is rich or lean by detecting the concentrate of oxygen present
in the exhaust gas.
Code No. Diagnostic Trouble Code Detecting Condition Trouble Area
Main oxygen sensor voltage is 0.45 V or less (lean)
for 90 sec. under conditions (a) and (b). (2 trip
detection logic)*
2
(a) Engine coolant temp.: 50C (122F) or more.
(b) Engine speed: 1,500 rpm or more
Open or short in main oxygen sensor circuit
Main oxygen sensor
Ignition system
ECM
25
*
1
Difference of air–fuel ratio feedback compensa-
tion value between right and left banks is more than
15 percent for 20 sec. or more under conditions (a)
and (b). (2 trip detection logic)*
2
(a) Engine coolant temp.: Between 70C (158F)
and 95C (203F)
(b) Engine speed: Idling
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction
(skipping teeth of timing belt)
Ignition system
Compression pressure
Volume air flow meter
ECM
26
Difference of air–fuel ratio feedback compensation
value between right and left banks is more than 15
percent for 20 sec. or more under conditions (a) and
(b). (2 trip detection logic)*
2
(a) Engine coolant temp.: Between 70C (158F)
and 95C (203F)
(b) Engine speed: Idling
Fuel line pressure (injector leak, blockage)
Mechanical system malfunction
(skipping teeth of timing belt)
Ignition system
Compression pressure
Volume air flow meter
ECM
*1: Only for California specification vehicles
*2: See page EG–331.
EG–376
–ENGINE TROUBLESHOOTING CIRCUIT INSPECTION
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