
DI-22
DIAGNOSTICS - ENGINE
DI21S-03
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,
temperature sensor and a control circuit installed in a plastic housing. The hot wire air flow meter works on
the principle that the hot wire and temperature sensor 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 mass air flow meter.
The circuit is constructed so that the platinum hot wire and temperature sensor provide a bridge circuit, with
the power transistor controlled so that the potential of A and B remains equal to maintain the set temperature.
B+
Temperature Sensor
Power Transister
Platinum Hot wire
A B
Output
Voltage
FI6929
S05741 A06106
DTC No. DTC Detecting Condition Trouble Area
S Open or short in mass air flow meter circuit
Open or short in mass air flow meter circuit with more than 3
P0100 S Mass air flow meter
sec. engine speed 4,000 rpm or less
S ECM
If the ECM detects DTC P0100 it operates the fail-safe function, keeping the ignition timing and injection
volume constantly 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 the CURRENT DATA.
Mass Air Flow Value (gm/sec.) Malfunction
S Mass air flow meter power source circuit open
0.0
S VG circuit open or short
271.0 or more S E2G circuit open
2001 SIENNA (RM787U)
Author : Date : 176
DI-23
DIAGNOSTICS - ENGINE
WIRING DIAGRAM
Engine Room J/B J/B No. 3 ECM
1 EFI 2 11 9
W 5 3 B-R
2I 2J 3B 3A
2 1
2F 2B
B-Y
4 EFI Relay 5
12
B-Y
IH1
1
10
P VG
B-L E11
3
19
W-B
R-B E2G
E11
2
Mass Air E2
FL
MAIN Flow Meter
B+
Battery
8
EA B-W MREL
E8
A14828
INSPECTION PROCEDURE
HINT:
Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool. Because freeze frame records
the engine conditions when the malfunction is detected. When troubleshooting, it is useful for determining
whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean
or rich, etc. at the time of the malfunction.
1 Connect OBD II scan tool or TOYOTA hand-held tester, and read value of mass
air flow rate.
PREPARATION:
(a) Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.
(b) Turn the ignition switch ON and push the OBD II scan tool or TOYOTA hand-held tester main switch
ON.
(c) Start the engine.
CHECK:
Read the mass air flow rate on the OBD II scan tool or TOYOTA hand-held tester.
RESULT:
Type I Type II
Mass Air Flow Rate (gm/sec.) 0.0 271.0 or more
Type I Go to step 2.
2001 SIENNA (RM787U)
Author : Date : 177
DI-24
DIAGNOSTICS - ENGINE
Type II Go to step 5.
2 Check voltage of mass air flow meter power source.
PREPARATION:
ON
(a) Disconnect the mass air flow meter connector.
(b) Turn the ignition switch ON.
CHECK:
1
Measure the voltage between terminal 1 of the mass air flow
(+) meter connector and body ground.
OK:
(-)
Voltage: 9 - 14 V
BE6653
P24310 A00099
NG Check for open in harness and connector be-
tween EFI main relay (Marking: EFI) and mass
air flow meter (See page IN-31 ).
OK
3 Check voltage between terminal VG of ECM connector and body ground.
PREPARATION:
VG (a) Remove the glove compartment (See page SF-83 ).
(b) Start the engine.
CHECK:
Measure the voltage between terminal VG of the ECM connec-
tor and body ground while the engine is idling.
(+) (-)
OK:
Voltage:
A02017 1.1 - 1.5 V (P or N position and A/C switch OFF)
OK Check and replace ECM (See page IN-31 ).
NG
4 Check for open and short in harness and connector between mass air flow meter
and ECM (See page IN-31 ).
NG Repair or replace harness or connector.
OK
2001 SIENNA (RM787U)
Author : Date : 178
DI-25
DIAGNOSTICS - ENGINE
Replace mass air flow meter.
5 Check continuity between terminal E2G of ECM connector and body ground.
PREPARATION:
E2G Remove the glove compartment (See page SF-83 ).
CHECK:
Check the continuity between terminal E2G of the ECM con-
nector and body ground.
OK:
Continuity (1 or less)
A02018 NG Check and replace ECM (See page IN-31 ).
OK
6 Check for open in harness and connector between mass air flow meter and ECM
(See page IN-31 ).
NG Repair or replace harness or connector.
OK
Replace mass air flow meter.
2001 SIENNA (RM787U)
Author : Date : 179