Temperature warning for over-heated catalytic converter
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Temperature warning for over-heated catalytic converter
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For certain markets the cars are equipped with a system which gives warning of catalytic converter overheating. This is to comply with laws concerning grass fires and the like.
The system consists of a temperature sensor which is located by the catalytic converter, a relay located in
relay position F
(LHD) or
C
(RHD) in the distribution centre in the dashboard and a warning lamp in the main instrument unit. When the catalytic converter's temperature reaches 825 ± 25C (1517 ± 45F), the warning lamp comes on. It does not go out until the temperature has fallen by about 10C (18F).
There is a fire shield fitted under the catalytic converter as a direct protection against ignition of ground vegetation.
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Description of the functioning
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When current (+15 circuit) is applied to relay pin 4 (i.e. the ignition is switched on), the relay grounds the warning lamp for about 3 seconds. Normally, the warning lamp then goes out and does not come on again until the catalytic converter's temperature exceeds the specified level. If the lamp stays on, there is a short in the temperature sensor circuit. If the current, which is constantly applied across temperature sensor relay pins 1 and 3, reaches a specific value due to changes in the sensor's resistance as the temperature rises, the relay is activated and the lamp comes on. Correspondingly, the lamp goes out when the temperature drops or if the current (+15 circuit) is interrupted (i.e. when the ignitions is switched off).
