Toyota 2.4L/22RE Air Flow Meter (AFM)

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Contents:

• Introduction
• AFM Testing
• Troubleshooting
• More Information

Introduction

The Toyota 22R-E engine is electronically fuel injected. As such they lack a mechanical carburetor and instead split the function of the carburetor into three parts, namely the Air Flow Meter in the air cleaner box, the throttle body and the fuel injector. The air flow meter uses a flapper vane and temperature sensor to detect the amount and temperature of the incoming air flow. The throttle body controls the air flow into the engine and the fuel injectors supply the proper amount of fuel to each piston depending upon operating conditions.

While this information is based upon the AFM system in the 22R-E engine, most of it applies to other Toyota EFI engines. For specific information, be sure to consult the service manual for your model engine. On the 22RE engine, the AFM is located atop the air filter box. In a stock engine compartment, this is in the driver's side front corner. In the image below, the AFM is dead center in the image:

Air Flow Meter location

Throttle Position Sensor:

AFM Testing:

The AFM is not designed to be adjusted, so it either works or doesn't work.

• To conduct the statis tests (with the engine off)
  • Unplug the connector at the AFM
    • Use a small screwdriver to gently pry the wire clipthat wraps around the connector out to each side to free the connector.
    • Once removed, you can push the wire clip back into place.
  • Using an ohm meter, measure the resistance between terminals as specified below:

    AFM Connector Pinouts

    FC

    E1

    E2

    VB

    VC

    VS

    THA

    Here are the static tests:

    Table 1: 22RE (2.4L-4 cyl) - AFM Static Testing

    Test	Between Terminals	Resistance / (ohms)	Temperature
    1.	E2 - VS	20 - 400	n/a
    2.	E2 - VC	100 - 300	n/a
    3.	E2 - VB	200 - 400	n/a
    4.	E2 - THA	10K - 20K 4K - 7K 2K - 3K 900-1300 400 - 700	-20°C (-4°F) +0°C (32°F) +20°C (68°F) +40°C (104°F) +60°C (140°F)
    5.	E1 - FC	Infinite/open	n/a

    Then if the above tests are OK, then you can test the actual operation of the air flow sensing portion of the AFM:

    • While measuring the resistances specified below, move the measuring plate inside the AFM
      • You'll need to remove the air tube from the AFM to access the measuring plate

    Table 2: 22RE (2.4L-4 cyl) - AFM Dynamic Testing

    Test	Between Terminals	Resistance / (ohms)	Measuring Plate Opening
    1.	E1- FC	Infinite/Open Zero/Short	Fully Closed Any opening
    2.	E2 - VS	20 - 400 20 -1000	Fully Closed Fully Closed to Fully Open

    Notes:

    1. The E1-FC connection is what triggers the fuel pump to operate via the Circuit Opening Relay
    2. On test #2, you should see the resistance generally increase as the AFM plate is moved from closed to open, but it may not be in a smooth linear fashion. The resistor track in the AFM is laser trimmed for calibration at the factory and you may see sections where the resistance first increases, the drops down a little before increasing some more. What you want to watch for are places where the resistance drops below 20 or above 1000 ohms (for example if it goes to infinite/open circuit) as that would indicate a problem.
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    Troubleshooting:

    Since the AFM has two basic functions, that of measuring air flow as well as turning on the fuel pump, problems can arise in these two areas. Without the fuel pump running, the engine will cut out and die from lack of fuel. If this happens, check the E1-Fc connection. If the engine runs overly rich or lean, especially at full throttle, the AFM could be the cause, if its telling the ECU that extra air is present (that isn't), the ECU (running on open loop mode at full throttle) would increase the fuel injected into the cylinder, causing the rich condition. Likewise, a too-low air flow reading my result in lean operation. For testing both the above conditions, an in-cab fuel pressure and Air/Fuel gauge is indispensible.

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    Other TPS/EFI related information:

    • My TPS Adjustment Writeup
    • A writeup on TPS operation is available on the ORC Toyota Tech section
    • Some tips on AirFlowMeter and TPS tweaks on the Celicas.org web page
    • An extensive collection of technical articles is available at AutoShop101.com
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    [Initial creation: 24.Jan.2000]

    [Last updated: Friday, 22-May-2009 07:54:30 PDT]