Circuit Description; Mass Air Flow Circuit Malfunction - Toyota T100 1996 Service Manual

DI−22
CIRCUIT INSPECTION
DTC P0100

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.
Thermistor
A
FI6929 FI7109
DTC No.
Open or short in mass air flow meter circuit with engine
P0100
speed 4,000 rpm or less (2 trip detection logic)
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.)
202.2 or more
1996 TOYOTA T100 (RM449U)
DIAGNOSTICS

Mass Air Flow Circuit Malfunction

B+
Power Transistor
Platinum Hot Wire
B
Output Voltage
DTC Detecting Condition
0.5
− ENGINE (3RZ−FE)
Platinum Hot Wire
S Open or short in mass air flow meter circuit
S Mass air flow meter
S ECM
S Mass air flow meter power source circuit open
S VG circuit open or short
S E3 circuit open
Thermistor
Trouble Area
Malfunction
DI0TC−03
A00043