The ECM uses the information from the downstream HO2S to enhance the signals from the upstream HO2S.
The downstream HO2S are similar in their construction to the upstream HO2S with the exception of the output signal to
the ECM. The output signal is a binary signal where the amplitude of the signal curve changes considerably when the
oxygen content in the exhaust gasses changes. The oxygen content of the exhaust gasses leaving the catalytic converter
are measured by comparing it with ambient air drawn into the HO2S.
Stop Lamp Switch
The stop lamp switch is attached to the brake pedal bracket, adjacent to the speed control inhibit switch. W hen the brake
pedal is pressed, a plate on the pedal moves away from the switch plunger allowing the plunger to extend and complete
the switch contacts.
The switch receives a permanent, fused battery voltage via the BJB and the CJB. The switch is connected to the ECM which
provides the ground path. The ground (battery voltage signal) is used by the ECM as a switch operation signal. The ground
from the switch is routed via the CJB to the ECM which allows the CJB to also determine the switch operation.
The CJB uses the completed ground when the switch is operated to activate the stop lamps.
The ECM can diagnose the operation of the stop lamp switch and the status of the switch can be read using a Land Rover
approved diagnostic system.
Ambient Air Temperature (AAT) Sensor
The AAT sensor is located in the underside of the Left Hand (LH) exterior door mirror. The sensor is a Negative
Temperature Co-efficient (NTC) thermistor element. The element resistance decreases as the sensor temperature
increases which produces a low signal voltage. The ECM supplies the sensor with a 5V reference voltage and a ground and
measures the returned signal voltage as an outside temperature.
The AAT signal is used by the ECM for a number of functions including engine cooling fan control and A/C compressor
displacement control. The ECM also transmits a message on the high speed CAN bus relating to the current outside
temperature for use by other control modules.
The ECM can diagnose the operation of the AAT sensor and the sensor output values can be read using a Land Rover
approved diagnostic system.
Fuel Pump Driver Module (FPDM)