Toyota 1 MZ–FE Manual page 444

EG2–444
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 temperature.
The hot wire is maintained at the set temperature by
controlling the current flow through the hot wire.
This current flow is then 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 tem–
perature.
DTC No. Diagnostic Trouble Code Detecting Condition
Open or short in mass air flow meter circuit with
P0l00
engine speed 4,000 rpm or less.
If the ECM detects diagnostic trouble code "P01 00" it operates the fail safe function, keeping the ignition
timing and injection volume constant and making it possible to drive the vehicle.
1MZ–FE ENGINE – CIRCUIT INSPECTION
Open or short in mass air flow meter circuit
Mass air flow meter
ECM
Trouble Area