AIR CONDITIONING: DESCRIPTION AND OPERATION (page 4 of 5)

AIR CONDITIONING

DESCRIPTION AND OPERATION

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Diagnostics
The ATC ECU performs a diagnostic check each time the ignition is switched on. To avoid nuisance fault indications 
at low light levels, the sunlight sensor is omitted from the diagnostic check. If a fault is detected, the audible warning 
sounds three times and the AUTO window on the control panel display flashes for 20 seconds. The ATC ECU then 
reverts to normal control but uses a default value or strategy for the detected fault. Faults are identified by performing 
a manual diagnostic check of the system.

A manual diagnostic check includes a check of the sunlight sensor, and is initiated by pressing and holding the AUTO 
switch and the air distribution switch, then turning the ignition switch from off to on. The audible warning sounds once 
and the indications on the control panel display illuminate. FC is shown in the LH temperature window and the results 
of the check are shown as a two digit fault code in the RH temperature window. If a fault is detected, the audible 
warning sounds three times and the AUTO window on the display flashes on and off for 20 seconds. If more than one 
fault is detected, the fault codes cycle in numerical order, at 1 Hz. The audible warning sounds as each fault code is 
shown. In low light conditions, to avoid false sunlight sensor fault indications, the sunlight sensor should be illuminated 
with a strong light source.

Diagnostic fault codes and fault descriptions

Code

Component

Fault

Default value/strategy

00

-

No fault found

-

11

In-car temperature sensor

Open or short circuit

25

°

C (77

°

F)

12

Ambient temperature sensor

Open or short circuit

10

°

C (50

°

F)

Cooling fan permanently on
Display shows "- -" if external air 
temperature selected

13

Thermistor

Open or short circuit

0

°

C (32

°

F)

14

Heater coolant temperature sensor

Open or short circuit

70

°

C (158

°

F)

21

Sunlight sensor, left output

Open or short circuit

No solar heating correction

22

Sunlight sensor, right output

Open or short circuit

No solar heating correction

31

LH temperature servo motor

Open or short circuit
Motor or flap mechanism seized

Servo motor locked in position

32

RH temperature servo motor

Open or short circuit
Motor or flap mechanism seized

Servo motor locked in position

33

Distribution servo motor

Open or short circuit
Motor or flap mechanism seized

Servo motor locked in position