P21242 FI7210
A00027
Atmosphere
Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust Gas
Cover
Ideal Air
−
Fuel Mixture
Output V
oltage
Richer
−
Air Fuel Ratio
−
Leaner
DI
−
40
−
DIAGNOSTICS
ENGINE
1996 LAND CRUISER (RM451U)
DTC
P0125
Insufficient Coolant Temp. for Closed Loop
Fuel Control
CIRCUIT DESCRIPTION
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three
−
way cata-
lytic converter is used, but for the 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 where by 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 ex-
haust gas in 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.
The 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 temp. of the exhaust gas is low) current flows to the heater
to heat the sensor for accurate oxygen concentration detection.
DTC No.
DTC Detecting Condition
Trouble Area
P0125
After the engine is warmed up, heated oxygen sensor (bank 1
sensor 2) output does not indicate RICH even once when
conditions (a), (b) and (c) continue for at least 1.5 min.
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40
−
100 km/h (25
−
62 mph)
(c) Closed throttle position switch: OFF
S
Open or short in heated oxygen sensor (bank 1 sensor 1)
circuit
S
Heated oxygen sensor (bank1 sensor 1)
DI5P9
−
02
Brought to you by BirfMark
Brought to you by BirfMark
Version 1.00 - 12/21/2010