Exhaust System Temperature Indicator: Description and Operation

Cars for certain markets are equipped with a monitoring system for catalytic converter overheating. The system consists of:
^ Temperature sensor 417
^ Electronic relay 415
^ Warning lamp 471

When catalytic converter temperature reaches 825 +/- 25°C, the warning lamp lights up and remains on until the temperature drops by about 10°C.

When current (+15 circuit) is applied to relay pin 1, the warning lamp is grounded and lights up for about 3 seconds. It does not come on again unless the temperature of the three-way catalytic converter exceeds the set limit.

As the temperature rises, the current flowing between pins 3 and 4 of the temperature sensor changes. When the resistance of the sensor changes by a sufficient amount, the relay function is activated and the warning lamp lights up.

Similarly, the warning lamp goes out when the temperature drops or when current (+15 circuit) is no longer applied to the relay, i.e. when the ignition is switched off.