1996 TOYOTA T100 air condition

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FI6929 FI7109A00043
B+
Power Transistor
Platinum Hot Wire
Output Voltage
A
B Thermistor
Thermistor
Platinum Hot Wire DI−22
− DIAGNOSTICSENGINE (3RZ−FE)
1996 TOYOTA T100 (RM449U)
CIRCUIT INSPECTION
DTC P0100 Mass Air Flow Circuit Malfunction
CIRCUIT DESCRIPTION
The mass air flow meter uses a platinum hot wire. The hot wire air flow meter consists of a platinum hot wire,
thermistor and a control circuit installed in a plastic housing. The hot wire air flow meter works on the principle
that the hot wire and thermistor located in the intake air bypass of the housing detect any changes in the
intake air temp.
The hot wire is maintained at the set temp. by controlling the current flow through the hot wire. This current
flow is ten measured as the output voltage of the air flow meter.
The circuit is constructed so that the platinum hot wire and thermistor provide a bridge circuit, with the power
transistor controlled so that the potential of ”A” and ”B” remains equal to maintain the set temp.
DTC No.DTC Detecting ConditionTrouble Area
P0100Open or short in mass air flow meter circuit with engine
speed 4,000 rpm or less (2 trip detection logic)Open or short in mass air flow meter circuit
Mass air flow meter
ECM
If the ECM detects DTC ”P0100” it operates the fail safe function, keeping the ignition timing and injection
volume constant and making it possible to drive the vehicle.
HINT:
After confirming DTC P0100 use the OBD II scan tool or TOYOTA hand−held tester to confirm the mass air
flow ratio from ”CURRENT DATA”.
Mass Air Flow Value (gm/sec.)Malfunction
0.5Mass air flow meter power source circuit open
VG circuit open or short
202.2 or moreE3 circuit open

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− DIAGNOSTICSENGINE (3RZ−FE)
1996 TOYOTA T100 (RM449U)
DTC P0101 Mass Air Flow Circuit Range/Performance
Problem
CIRCUIT DESCRIPTION
Refer to DTC P0100 on page DI−22.
DTC No.DTC Detecting ConditionTrouble Area
P0101
Conditions (a), (b) and (c) continue with engine speed 900
rpm or less:
(2 trip detection logic)
(a) Closed throttle position switch: ON
(b) Mass air flow meter output > 2.2 V
(c) THW  70°C (158°F)
Mass air flow meter
Conditions (a) and (b) continue with engine speed 1,850 rpm or
more:
(a) VTA  0.75 V
(b) Mass air flow meter output < 1.0 V
WIRING DIAGRAM
Refer to DTC P0110 (Intake Air Temp Circuit Malfunction) on page DI−27 for the WIRING DIAGRAM.
INSPECTION PROCEDURE
1 Are there any other codes (besides DTC P0101) being output?
YES Go to relevant DTC chart.
NO
Replace mass air flow meter.
DI0TD−02

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(fig.1)
Acceptable
Resistance kΩ
− 20 0 20 40 60 80 100
(− 4) 32 68 104 140 176 212 30
20
10
5
3
2
1
0.5
0.3
0.2
0.1
Temp.°C (F°)
− DIAGNOSTICSENGINE (3RZ−FE)
DI−27
1996 TOYOTA T100 (RM449U)
DTC P0110 Intake Air Temp. Circuit Malfunction
CIRCUIT DESCRIPTION
The intake air temp. sensor is built into the air cleaner cap and
sensors the intake air temp.
A thermistor built in the sensor changes the resistance value
according to the intake air temp. The lower the intake air temp.,
the greater the thermistor resistance value, and the higher the
intake air temp., the lower the thermistor resistance value (See
fig.1).
The intake air temp. sensor is connected to the ECM (See be-
low). The 5 V power source voltage in the ECM is applied to the
intake air temp. sensor from the terminal THA via a resistor R.
That is, the resistor R and the intake air temp. sensor are con-
nected in series. When the resistance value of the intake air
temp. sensor changes in accordance with changes in the intake
air temp., the potential at terminal THA also changes. Based on
this signal, the ECM increases the fuel injection volume to im-
prove driveability during cold engine operation.
If the ECM detects the DTC ”P0110”, it operates the fail safe
function in which the intake air temp. is assumed to be 20°C
(68°F).
DTC No.DTC Detecting ConditionTrouble Area
P0110Open or short in intake air temp. sensor circuit
Open or short in intake air temp. sensor circuit
Intake air temp. sensor
ECM
HINT:
After confirming DTC P110 use the OBD II scan tool or TOYOTA nand−held tester to confirm the intake air
temp. from ”CURRENT DATA”.
Temp. DisplayedMalfunction
− 40°C (− 40°F)Open circuit
140°C (284°F) or moreShort circuit
DI0TE−03

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Throttle Position
SensorECM
VCC
VTA
IDL
E25 V
B+
− DIAGNOSTICSENGINE (3RZ−FE)
DI−39
1996 TOYOTA T100 (RM449U)
DTC P0120 Throttle/Pedal Position Sensor/Switch ”A”
Circuit Malfunction
CIRCUIT DESCRIPTION
The throttle position sensor is mounted in the throttle body and
detects the throttle valve opening angle. When the throttle valve
is fully closed, the IDL contacts in the throttle position sensor
are on, so the voltage at terminal IDL of the ECM becomes
0 V. At this time, a voltage of approximately 0.3 − 0.8 V is applied
to terminal VTA of the ECM. When the throttle valve is opened,
the IDL contacts go off and thus the power source voltage of
approximately 12 V in the ECM is applied to terminal IDL of the
ECM. The voltage applied to terminal VTA of the ECM in-
creases in proportion to the opening angle of the throttle valve
and becomes approximately 3.2 − 4.9 V when the throttle valve
is fully opened. The ECM judges the vehicle driving conditions
from these signals input from terminals VTA and IDL, and uses
them as one of the conditions for deciding the air−fuel ratio
correction, power increase correction and fuel−cut control etc.
DTC No.DTC Detecting ConditionTrouble Area
P0120
Condition (a) or (b) continues:
(a) VTA < 0.1 V, and closed throttle position switch is OFF
(b) VTA > 4.9 VOpen or short in throttle position sensor circuit
Throttle position sensor
ECM
HINT:
If there is open circuit in IDL line, DTC P0120 does not indicate.
After confirming DTC P0120 use the OBD II scan tool or TOYOTA hand−held tester to confirm the
throttle valve opening percentage and closed throttle position switch condition.
Throttle valve opening position
expressed as percentage
Trouble Area
Throttle valve fully closedThrottle valve fully open
0 %0 %VCC line open
VTA line open or short
100 %100 %E2 line open
DI0TH−03

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A00027
Atmosphere
Flange
Platinum Electrode
Solid Electrolyte
(Zirconia Element)
Platinum Electrode
Heater
Coating (Ceramic)
Exhaust GasCoverIdeal Air−Fuel Mixture
Output Voltage
Richer − Air Fuel Ratio − Leaner DI−44
− DIAGNOSTICSENGINE (3RZ−FE)
1996 TOYOTA T100 (RM449U)
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
catalytic 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 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 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.
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 ConditionTrouble Area
P0125
After engine is warmed up, heated oxygen sensor output
does not indicate RICH even once when conditions (a), (b),
(c) and (d) 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
(d) 140 sec. or more after starting engine
Open or short in heated oxygen sensor (bank 1 sensor 1)
circuit
Heated oxygen sensor (bank 1 sensor 1)
HINT:
After confirming DTC P0125 use the OBD II scan tool or TOYOTA handheld tester to confirm voltage output
of heated oxygen sensor from "CURRENT DATA".
If voltage output of heated oxygen sensor is 0 V, heated oxygen sensor circuit may be open or short.
DI0TJ−02

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− DIAGNOSTICSENGINE (3RZ−FE)
1996 TOYOTA T100 (RM449U)
INSPECTION PROCEDURE
1 Check for open and short in harness and connector between ECM and heated
oxygen sensor (See page IN−26).
NG Repair or replace harness or connector.
OK
2 Check for heated oxygen sensor data.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand−held tester to the DLC3.
(b) Warm up the engine to normal operating temp.
CHECK:
Read heated oxygen sensor output voltage and short−term fuel trim.
HINT:
Read the values for the same bank.
RESULT:
PatternHeated oxygen sensor output voltageShort−term fuel trim
1Lean condition (Changes at 0.55 V or less)Changes at about + 20 %
2Rich condition (Changes at 0.4 V or more)Changes at about − 20 %
3Except 1 and 2
1, 2 Check fuel trim system (See page DI−55).
3

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DI−53
1996 TOYOTA T100 (RM449U)
DTC P0136 Heated Oxygen Sensor Circuit Malfunction
(Bank 1 Sensor 2)
CIRCUIT DESCRIPTION
Refer to DTC P0125 on page DI−44.
DTC No.DTC Detecting ConditionTrouble Area
P0136
Voltage output of heated oxygen sensor (bank 1 Sensor 2)
remains at 0.4 V or more or 0.5 V or less when vehicle is driv-
en at 50 km/h
(31 mph) or more after engine is warmed up
(2 trip detection logic)
Heated oxygen sensor
HINT:
Sensor 2 refers to the sensor farther away from the engine body.
WIRING DIAGRAM
Refer to DTC P0125 on page DI−44.
INSPECTION PROCEDURE
1 Are there any other codes (besides DTC P0136) being output?
YES Go to relevant DTC chart.
NO
2 Check for open and short in harness and connector between ECM and heated
oxygen sensor (See page IN−26).
NG Repair or replace harness or connector.
OK
DI0TN−02

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DI−55
1996 TOYOTA T100 (RM449U)
DTC P0171 System too Lean (Fuel Trim)
DTC P0172 System too Rich (Fuel Trim)
CIRCUIT DESCRIPTION
Fuel trim refers to the feedback compensation value compared against the basic injection time. Fuel trim
includes short−term fuel trim and long−term fuel trim.
Short−term fuel trim is the short−term fuel compensation used to maintain the air−fuel ratio at its ideal
theoretical value. The signal from the heated oxygen sensor indicates whether the air−fuel ratio is RICH or
LEAN compared to the ideal theoretical value, triggering a reduction in fuel volume if the air−fuel ratio is rich,
and an increase in fuel volume if it is lean.
Long−term fuel trim is overall fuel compensation carried out long−term to compensate for continual deviation
of the short−term fuel trim from the central value due to individual engine differences, wear over time and
changes in the usage environment.
If both the short−term fuel trim and long−term fuel trim are LEAN or RICH beyond a certain value, it is de-
tected as a malfunction and the MIL lights up.
DTC No.DTC Detecting ConditionTrouble Area
P0171
When air fuel ratio feedback is stable after engine warming
up, fuel trim is considerably in error on RICH side
(2 trip detection logic)
Air intake (hose loose)
Fuel line pressure
Injector blockage
Heated oxygen sensor (bank 1 sensor 1) malfunction
Mass air flow meter
Engine coolant temp. sensor
P0172
When air fuel ratio feedback is stable after engine warming
up, fuel trim is considerably in error on LEAN side
(2 trip detection logic)
Fuel line pressure
Injector leak, blockage
Heated oxygen sensor (bank 1 sensor 1) malfunction
Mass air flow meter
Engine coolant temp. sensor
HINT:
When the DTC P0171 is recorded, the actual air−fuel ratio is on the LEAN side. When DTC P0172 is
recorded, the actual air−fuel ratio is on the RICH side.
If the vehicle runs out of fuel, the air−fuel ratio is LEAN and DTC P0171 is recorded. The MIL then
comes on.
If the total of the short−term fuel trim value and long−term fuel trim value is within ± 25 %, the system
is functioning normally.
INSPECTION PROCEDURE
1 Check air induction system (See page MF−1).
NG Repair or replace.
OK
DI0TO−03