TEST 1: Making Sure The MAF Sensor Is Getting Power

Making Sure The MAF Sensor Is Getting Power. How To Test The 1990, 1991, 1992, 1993, and 1994 Lexus LS400 MAF Sensor

The very first thing that we'll do is check that the MAF sensor is receiving 5 Volts.

The light blue with red stripe (LT BLU/RED) wire, of the MAF sensor connector, is the one that provides these 5 Volts.

The LT BLU/RED wire is labeled with the #4 arrow in the photo above.

These are the test steps:

  1. 1

    Put the multimeter in VOLTS DC mode and disconnect the MAF sensor from its electrical connector.

  2. 2

    Probe the LT BLU/RED wire of the MAF sensor connector using an appropriate tool.

    The LT BLU/RED wire is labeled with the #4 arrow in the photo above.

  3. 3

    Connect the black multimeter probe to the battery negative (-) post.

  4. 4

    Turn the key ON but don't crank or start the engine.

  5. 5

    The multimeter should read 5 Volts DC if power is available.

Let's interpret your test result:

CASE 1: Your multimeter registered 5 Volts DC. This is the correct and expected test result.

Your next step is to go to: TEST 2: Making Sure The MAF Sensor Is Getting Ground

CASE 2: Your multimeter DID NOT register 5 Volts DC. This test result tells you that the MAF sensor is not getting power. Without power, it will not function.

Your next step is to find out why these 5 Volts are missing and restore them.

TEST 2: Making Sure The MAF Sensor Is Getting Ground

Making Sure The MAF Sensor Is Getting Ground. How To Test The 1990, 1991, 1992, 1993, and 1994 Lexus LS400 MAF Sensor

Now that you have confirmed that your Lexus LS400's MAF sensor is getting power, the next step is to make sure it's getting Ground.

The brown (BRN) wire, of the MAF sensor connector, is the one that provides chassis Ground.

The BRN wire is labeled with the #5 arrow in the photo above.

We'll do a simple multimeter voltage test to confirm the presence of Ground.

These are the test steps:

  1. 1

    Place your multimeter in Volts DC mode and turn the key to its OFF position.

  2. 2

    Probe the BRN wire of the MAF sensor with the black multimeter test lead using an appropriate tool.

    The BRN wire is labeled with the #5 arrow in the photo above.

  3. 3

    Connect the red multimeter probe to the battery positive (+) post.

  4. 4

    The multimeter should read 10 to 12 Volts DC if Ground is available.

Let's interpret your test result:

CASE 1: Your multimeter registered 10 to 12 Volts DC. This is the correct and expected test result.

Your next step is to go to: TEST 3: Testing The MAF Signal With A Multimeter

CASE 2: Your multimeter DID NOT register 10 to 12 Volts DC. This test result tells you that the MAF sensor is not getting Ground. Without Ground, it will not function.

Your next step is to find out why Ground is missing and restore it.