Understanding the Toyota B1479 Code and no AC Condition

Learn what a Toyota B1479 code means and why your AC doesn’t work

For Toyota owners, one of the potential culprits behind an AC system failure is the B1479 trouble code. This article will delve into the meaning of the Toyota B1479 code, its causes, and the steps to diagnose and resolve the issue, ensuring your car’s AC system functions efficiently.

Late-model Toyota vehicles use a refrigerant flow sensor in addition to the normal low and high-pressure switches. The flow sensor is located in the AC compressor. The ECM uses information from the flow sensor to vary the engine idle speed to prevent stalling. If the sensor is bad, the AC amplifier won’t send the proper digital signal to the ECM, and the ECM won’t engage the AC compressor clutch. You wind up with a Toyota B1479 code and no AC condition.

The most common cause is a bad flow sensor

Start the diagnosis with the scan tool. A bad flow sensor will usually show as B1479 open or short in the AC flow sensor circuit trouble code.

Then, test the Toyota AC flow sensor

1. Check for a 5-volt reference signal on the white wire

2. Check for flow sensor voltage on the red wire.

With the AC OFF and blower switch OFF, the voltage on the red wire should be 3.8 to 4.2 volts.

With the AC ON and Blower on HIGH, the voltage on the red wire should be 0.7 to 3.8-volts.

If the voltage is less than 0.7 or higher than 4.2, the sensor is bad

If there is no signal on the red wire but you see a 5-volt reference on the white wire, the sensor is bad

Replace the sensor

To replace the AC flow sensor, you must first evacuate the system. Measure how much oil comes out of the refrigerant so you can replace it. Then, replace the sensor.

Refill the oil with the amount you removed. Then evacuate the system again, Recharge using the recommended amount.

How the AC flow sensor works

The Toyota AC flow sensor in the compressor receives a 5-volt reference voltage from the AC amplifier located to the right of the accelerator pedal. It varies the output voltage back to the AC amplifier based on refrigerant flow.

Use your scan tool to see if the ECM is receiving an AC ON request from the AC amplifier. If you don’t see that request, perform these tests.

©, 2019 Rick Muscoplat