Exhaust System Temperature Indicator: Description and Operation

A warning lamp for catalytic converter overheating is fitted on cars for certain markets.

A voltage is applied to the EXH relay which operates when the temperature of the catalytic converter reaches 825 ± 25°C, causing the warning lamp to be grounded via pin 12 (12p-2) of the main instrument display panel connector.

The lamp will then remain alight until the temperature drops by about 10°C.

When the ignition is switched on, the lamp is tested for about 3 seconds. If the temperature is within normal limits the lamp will go out.