How To Test a Scion xB IAC Valve

How To Test a Scion xB IAC Valve


The xB IAC valve is also called your idle air control valve. It’s primary purpose is to maintain the idle in your 1NZ-FE engine. When your Scion engine is idling, this valve uses an electronic bypass to allow more or less air into the intake manifold. This device maintains the proper idle, and it’s cooled by two engine coolant ports.

When your xB IAC valve starts to fail on you, Scion idle problems will soon follow. These common Scion xB problems can range from poor performance, inconsistent idle to loud buzzing under your hood. Today I’ll be showing you how to test the xB IAC valve in a 2006 Scion.

Testing a Scion xB IAC Valve 12Of course one of the most obvious symptoms of a failed xB IAC valve is your Scion check engine light.

When you see your xB check engine light on, you’ll need a OBDII scan tool to check the stored DTC code.

In order to test the xB IAC valve, you will need a digital multimeter. This DIY testing tutorial will walk you through the testing of your idle air control valve in your 1NZ-FE engine.

Some of the most common Scion issues with your xB IAC valve involve a poor engine idle, or your engine not staying on. This unit is connected to two coolant lines and a three pin weatherproof connector. We’ll be using our digital multimeter to test the operation of your xB IAC valve.

Testing your xB IAC Valve for Power

To begin our guide you’ll need to open your hood and locate your xB IAC valve. This unit is mounted to the back of your intake manifold. Insert your Scion xB ignition key and turn the ignition switch to the “ON” position.

Testing a Scion xB IAC Valve 1

The first part of our xB IAC valve testing guide involves testing the power and ground circuits. Once you’ve got the idle air control valve unplugged, look at the front of the unplugged harness. Check the xB IAC valve wiring guide below to check the wires that you will be checking for power and ground.

Place the black lead of your multimeter to the negative terminal on your Scion battery. Now you’ll be using the positive lead or the red lead of the multimeter and gently probing the front of PIN B or the middle wire.

Test a Scion XB IAC valveThis wire should be sending your xB IAC valve a switched power signal. If you have power here or between 9 and 14 volts, check the pin labeled GND in our wiring diagram.

You can do this by switching the leads on the multimeter.

Put the positive lead on the positive terminal of your battery and probe the wire from the ENGINE harness with the black lead. You should have 12 volts here in this test.

If you have both power and ground, your xB IAC valve is receiving what it needs to operate. The next part of our testing guide will be covering the xB IAC itself. Inspect your intake pipe and check for any leaks or cracks in the intake tract.

When you hear buzzing under your hood or when your xB IAC valve is operating, this may be an early sign of failure. You should also check the coolant lines that run to the idle air control valve to make sure they are not leaking.

The next part of this guide is to check for an open condition to your xB ECU. This engine control unit is mounted behind your glovebox and may require you to remove the glovebox cover in order to access the ECU.

Test a Scion XB IAC valve 6The wires you are looking for are labeled in E01 and RSD in the E5 position of your Scion ECU.

Disconnect the idle air control valve and then disconnect the left most ECU plug. Now you need to check for standard resistance between the DUTY wire on the idle air control valve harness and the RSD wire of your Scion ECU. The next combination of wires to check for an open condition is the GND wire of the idle air control valve harness and your E01 ECU wire.

If everything in our testing guide checks out, but your idle air control valve is still not working correctly. You need to remove the bad unit and install a new IAC for your Scion. Have any questions about this DIY article? Leave us a comment below and let us know!