Toyota Supra Air Con Diagnostics

How to diagnose air-con not working on a Toyota Supra. Faulty air con? Get the diagnostic codes out of your Supra using the following method.

This applies to Toyota's Mk4 Supra

With the ignition switched off, hold down the two larger heater control buttons shown below, then switch the ignition on. (Recirc and Auto buttons). Any fault codes stored in the system will then flash the LEDs. See below for diagnostic codes.

Toyota Supra heater control panel

Toyota Supra Air Con Fault Codes

LED NumberButtonFault
3 Auto Normal
6 Face Open or short in room temperature sensor circuit
7 Foot/Face Open or short in ambient temperature sensor circuit
8 Foot Open or short in evaporator temperature sensor circuit
9 Foot/Demist Open or short in engine coolant temperature sensor circuit
10 Front Demist Fault in solar sensor circuit. (Might be normal if in dim light conditions. Try again while in bright sunlight, or shine a torch into the solar sensor at the base of the windscreen.)
5 A/C Engine speed 450 rpm or more / Ratio between engine and compressor rpm deviates 20% or more in comparison to normal operation
2b Freshair Abnormal refrigerant pressure
2a Recirculate Short to ground or power source circuit in air mix damper position sensor circuit
L-LO? Short to ground or power source circuit in air outlet damper position sensor circuit
L-M2? Air mix damper position sensor value does not change even if A/C amplifier signals the air mix damper control servo motor to operate
L-HI? Air outlet damper position sensor value does not change even if A/C amplifier signals the air outlet damper control servo motor to operate
Page Updated 08/05/10