Select Monitor Adapter
Subaru Diagnostic Ports
How to build a PC adapter

Engine Control Unit (ECU)
Reading Error Codes
Reverse Engineering
ROM images

Transmission Control Unit (TCU)
Reading Error Codes
Reverse Engineering
Power Mode
ROM images

Other Control Units
Air Conditioning Unit
4WS Control Unit
Cruise Control Unit

OBD2 Information
Select Monitor Cartridge

Links to other sites

Custom TCU Development

Zexel Air Conditioning Control Unit

We haven't investigated the diagnostic features of the Air Conditioning Control Unit in much detail. The data returned by querying it suggests that it is a much simpler device than the ECU and TCU. There appear to be only 32 addressable locations.

Here are the values returned by querying each address.

00000000   00 9D 8F 98 00 00 40 AF B5 70 6B 0E 6E 00 00 00
00000010   00 59 00 02 00 81 00 00 00 00 00 00 00 00 00 00

Location 02 seems to hold the outside temperature. The formula appears to be (x-102)/3 in degrees Celsius. In the example, the value 8F represents 20.5 degrees

Location 09 and 0A seem to be related to the position of the mode doors.

Location 0B seems to hold the temperature set on the panel. The formula is 18+(x*0.5) degrees Celsius. In the example, the value 0E represents 25 degrees.

Location 0D seems to be related to the fan speed.

Location 0E seems to indicate the intake position. 00=Recirc, 02=Outside.

Location 0F seems to indicate which button is being pressed on the control panel. See picture at top of page. 01=Recirc, 02=Demist, 03=Fan, 06=A/C, 07=Temp+, 08=Temp-, 09=Auto, 0A=Off, 0B=Out_Temp, 0C=Mode.

The control panel is slightly different on a USDM SVX. See picture below. The buttons are as follows: 01=Recirc, 02=Demist, 03=High, 04=Med, 05=Lo, 06=Econ, 09=Auto, 0A=Off, 0B=Out_Temp, 0C=Vent

Further investigation is required to discover the meaning of the other memory locations. We have not tried writing data to the unit to see whether it can be controlled via the select monitor interface.

The locations in the table below were extracted from the Select Monitor Cartridge.
000B" Tset (F01) "
000C" To (F02) "
0001" Troom (F03) "
0002" Tamb (F04) "
0003" Tevp (F05) "
0004" Qsun (F06) "
0004" Tsun (F07) "
0005" Tref (F08) "
0006" Tw (F09) "
0007" AMRset (F10) "
0008" AMRpot (F11) "
0009" MODEset (F12) "
000A" MODEpot (F13) "
000D" BLW (F14) "
000E" Intak (F15) "
0010" Isol (F16) "
0011" EGItoA/C(F17) "
000F" Sw (FA0) "
0012" DIAG.COD(FB0) "