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 416
^ Warning lamp 47L

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 pin 4 of the relay, the warning lamp is connected to ground and lights up for about 3 seconds. The lamp will not light up again unless the catalytic converter temperature exceeds the preset limit.

As the temperature rises, the current between pins 3 and 1 of the temperature sensor changes. When the change in the resistance of the sensor is sufficiently great, 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.

A heat shield designed to prevent ground vegetation from catching fire is mounted under the three-way catalytic converter and intermediate pipe.