By Richard Hawkins, MACS Contributor

If you work on Toyota, Lexus and Scion A/C systems, chances are that you have encountered a B1479 diagnostic trouble code on a system that will not operate.

If you have not encountered one yet, chances are that you will. This is a code that pertains to issues with the A/C flow sensor circuit, which was used on various

Toyota-built vehicles from 2010 to 2018.

The A/C flow sensor is installed in a cavity on top of the compressor and is used to detect the amount of refrigerant flow. (Please see picture #1.)

The A/C flow sensor converts the amount of refrigerant flow that is detected to a voltage value to send it to the air conditioning amplifier assembly.

The voltage value sent from the A/C flow sensor changes depending on the amount of refrigerant flow. As the amount of refrigerant flow becomes larger, the voltage becomes lower. As the amount of refrigerant flow becomes smaller, the voltage becomes higher.

The air conditioning amplifier assembly supplies 5 V to the A/C flow sensor, and monitors changes in the voltage value sent from the A/C flow sensor. The air conditioning amplifier assembly then sends a signal to the ECM via CAN communication to allow the ECM to control the engine speed while the air conditioning is on.

When this DTC is encountered, diagnostic information indicates that the condition is an open or short in the A/C flow sensor circuit. The trouble areas are as follows:

• The flow sensor.
• Wiring harness or connector between the flow sensor and the A/C amplifier assembly.
• A/C amplifier assembly.

Most information systems provide some detailed diagnostic information. Based on experience with tech calls over the years, the flow sensor ends up being the problem a very high percentage of the time. In the past, if that was the case, it was necessary to install a new compressor because the flow sensor was not available separately.

Fortunately, MACS members Dorman and Omega/Santech both have these units available now: Dorman’s part number is 926-818 and the Omega/Santech part number is MT13001.

If you happen to be replacing one of these compressors for an issue other than the flow sensor, it would be a good idea to remove the flow sensor before the compressor is put in the core or scrap pile.

Set it aside, as it can be used in the future for testing purposes.

I’m not an advocate of replacing parts instead of doing diagnostics; however in this case, because of the high probability of a flow sensor being bad and the ease with which one can be installed, having a known good test flow sensor handy to install can save some time in determining if there is indeed a flow sensor problem. Please see picture #2.

If installing the known good test flow sensor corrects the B1479 issue, then one of the Dorman or Omega/Santech units can be sourced to fix the problem. If the problem still exists after installing the known good test flow sensor, then it will be necessary to utilize the diagnostic procedure provided in your information system to dig further into the issue.

This article appears courtesy of the Mobile Air Climate Systems Association (MACS) www.macsmobileairclimate.org

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