Toyota Sienna Service Manual: Mass or Volume Air Flow Circuit

DESCRIPTION

The Mass Air Flow (MAF) meter is a sensor that measures the amount of air flowing through the throttle valve. The ECM uses this information to determine the fuel injection time and to provide appropriate airfuel ratio. Inside the MAF meter, there is a heated platinum wire which is exposed to the flow of intake air.

By applying a specific electrical current to the wire, the ECM heats it to a specific temperature. The flow of incoming air cools both the wire and an internal thermistor, changing their resistance. To maintain a constant current value, the ECM varies the voltage applied to these components in the MAF meter. The voltage level is proportional to the air flow through the sensor, and the ECM uses it to calculate the intake air volume.

The circuit is constructed so that the platinum hot wire and the temperature sensor provide a bridge circuit, and the power transistor is controlled so that the potentials of A and B remain equal to maintain the predetermined temperature.

HINT:

When any of these DTCs are set, the ECM enters fail-safe mode. During fail-safe mode, the ignition timing is calculated by the ECM, according to the engine RPM and throttle valve position. Fail-safe mode continues until a pass condition is detected.

HINT:

When any of these DTCs are set, check the air-flow rate by selecting the following menu items on an intelligent tester: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / MAF.

MONITOR DESCRIPTION

If there is a defect in the MAF meter or an open or short circuit, the voltage level deviates from the normal operating range. The ECM interprets this deviation as a malfunction in the MAF meter and sets a DTC.

Example: When the sensor voltage output remains less than 0.2 V, or more than 4.9 V, for more than 3 seconds, the ECM sets a DTC.

If the malfunction is not repaired successfully, a DTC is set 3 seconds after the engine is next started.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

TYPICAL MALFUNCTION THRESHOLDS

COMPONENT OPERATING RANGE

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT:

Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air-fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

1 READ VALUE OF INTELLIGENT TESTER (MASS AIR FLOW RATE)

(a) Connect the intelligent tester to the DLC3.

(b) Start the engine.

(c) Turn the tester on.

(d) Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / MAF.

(e) Read the values displayed on the tester.

Result

*1: The value must be changed when the throttle valve is open or closed.

2 INSPECT MASS AIR FLOW METER (POWER SOURCE VOLTAGE)

(a) Disconnect the M6 Mass Air Flow (MAF) meter connector.

(b) Turn the ignition switch to the ON position.

(c) Measure the voltage according to the value(s) in the table below.

Standard voltage

(d) Reconnect the MAF meter connector.

3 INSPECT ECM (VG VOLTAGE)

(a) Start the engine.

(b) Measure the voltage between the terminals of the E9 ECM connector.

HINT:

The transmission gear selector lever should be in the P or N position and the A/C switch should be turned off.

Standard voltage

4 CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)

(a) Disconnect the M6 MAF meter connector.

(b) Disconnect the E9 ECM connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard resistance :

(d) Reconnect the MAF meter connector.

(e) Reconnect the ECM connector.

REPLACE MASS AIR FLOW METER (See page ES-504)

5 INSPECT FUSE (EFI NO. 2 FUSE)

(a) Remove the EFI No. 2 fuse from the engine room relay block.

(b) Measure the resistance according to the value(s) in the table below.

Standard resistance: Below 1 Ω

(c) Reinstall the EFI No. 2 fuse.

REPAIR OR REPLACE HARNESS OR CONNECTOR (MASS AIR FLOW METER - EFI RELAY)

6 INSPECT ECM (SENSOR GROUND)

(a) Measure the resistance according to the value(s) in the table below.

Standard resistance

7 CHECK HARNESS AND CONNECTOR (MASS AIR FLOW METER - ECM)

(a) Disconnect the M6 MAF meter connector.

(b) Disconnect the E9 ECM connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard resistance:

(d) Reconnect the MAF meter connector.

(e) Reconnect the ECM connector.

REPLACE MASS AIR FLOW METER (See page ES-504)