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How to Check Air Conditioning Diagnostic Codes
1990-1994 Lexus LS400

By LexLS.com

Before doing anything read my disclaimer & safety info.



This will show you how to check A/C codes to see if there are any problems in your A/C system. Hopefully your system is normal, but if you're having problems with your A/C system these codes may help you pinpoint what's wrong. Please note that this will NOT tell you the status of the refrigerant.


1) First perform an indicator check to see if all the lights are working properly. Press and hold the AUTO & REC buttons and then start the car. Release the buttons after the car has started. All the lights should light up and go off 4 times in a row at one second intervals. You should also hear a beep as the indicators light up. After the indicators blink 4 times you're in A/C diagnostic mode.

2) Read the code displayed on the LCD. Here you see a code 21; this can happen if you're not in light because it refers to the solar sensor.

3) Here's what normal will look like, code 00. When the codes are displayed they blink and beep. Here are all the codes that can be displayed.........

Code - Meaning

00 - Normal

11 - Open or short in room temperature sensor circuit.

12 - Open or short in ambient temperature sensor circuit.

13 - Open or short in evaporator temperature sensor circuit.

14 - Open or short in water temperature sensor circuit.

21* - Open or short in solar sensor circuit.

22* - Compressor motor locked. And/or, open or short in compressor lock sensor circuit.

31 - Open or short in air mix damper position sensor circuit.

32 - Open or short in air inlet damper position sensor circuit.

33 - Open in air mix damper position sensor circuit. Or, open or short in air mix servomotor circuit. Or, air mix servomotor locked.

34 - Open in air inlet damper position sensor circuit. Or, open or short in air inlet sensor servomotor circuit. Or, air inlet servomotor locked.

* - These are detected only when they are the current troubles. Other codes detect both current trouble (beep) and past trouble (no beep).

A/C indicator light blinks - This means your A/C compressor is locked. It's happened to me before and I needed a new (rebuilt) compressor installed.


4) Once you've read any codes you can proceed to performing an actuator check by pressing the REC button. This will start a check of different combinations for the system starting with code 20 and moving up to 29. To cancel this or the previous diagnostic mode simply press the OFF button.



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Last revised: Sunday, 29-Oct-2023 15:46:14 EDT