740 L4-2320cc 2.3L DOHC B234F (Can) (1992)
Throttle position (TP) switch
Sends signals to the MFI and DI system control modules that the throttle is closed or wide open.
In the B204FT/GT the TP switch also contains a potentiometer which sends the TC control system information about the throttle position.
TC models do not use the full load switch.
Heated oxygen sensor (HO2S)
Normally 14.7 kg air to 1 kg fuel is given as the ideal mixture for complete combustion. This mixture is called lambda = 1. The mixture can be
gauged by measuring the oxygen content of the exhaust gases after combustion by using an HO2S.
The HO2S produces a voltage signal proportional to the oxygen content in the exhaust gases. This signal alternates from high to low at the ideal
mixture of 14.7 kg air/1 kg fuel. A rich mixture produces a high voltage while a weak mixture produces a low voltage. This voltage varies between
0.1-0.9 volt. The control module bases the quantity of fuel injected on this signal so as to achieve the ideal mixture, lambda = 1.
The HO2S will only operate above a certain temperature, approx. 285°C (545°F). It is electrically heated so that it reaches operating temperature
quickly. When the ignition is switched on a current is applied to a PTC resistor, the resistance of which increases with temperature. This provides a
short warm up time and keeps the sensor at the correct operating temperature when the exhaust gas temperature is low.
In engines without a TWC (B 230 GT, B 204 GT), i.e engines for markets where unleaded gasoline is not fully available, an HO2S which can
withstand leaded fuel must be used. However, this HO2S has a limited lifespan and must be replaced regularly.