ENGINE MANAGEMENT SYSTEM - V8
Heated Oxygen Sensors (HO2S) (C0642)
The market requirement dictates how many HO2S are fitted to the vehicle.
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4 sensors are fitted to all NAS and EU-3 vehicles.
2 sensors fitted to all UK, European, Australia and Japanese pre EU-3 specification vehicles.
No sensors fitted to ROW vehicles.
The HO2S monitor the oxygen content of the exhaust gases. By positioning the sensors one for each bank upstream
of the catalytic converter in the exhaust pipe, the ECM can control fuelling on each bank independently of the other.
This allows greater control of the air:fuel ratio and maintains optimum catalyst efficiency. On NAS vehicles the ECM
also uses two HO2S positioned downstream of the catalytic converters in the exhaust pipe to monitor catalytic
converter efficiency. The ECM is able to achieve this by comparing the values of the upstream HO2S and the down
stream sensor for the same bank. These comparative values form part of the ECM OBD strategy.
The HO2S uses zirconium contained in a galvanic cell surrounded by a gas permeable ceramic, this produces an
output voltage proportional to the ratio difference between the oxygen in the exhaust gases and to the ambient
oxygen.
The HO2S operates at approximately 350 °C (662 °F). To achieve this temperature the HO2S incorporate a heating
element which is controlled by a PWM signal from the ECM. The elements are activated immediately after engine
starts and also under low engine load conditions when the exhaust gas temperature is insufficient to maintain the
required HO2S temperature. If the heater fails, the ECM will not allow closed loop fuelling to be implemented until the
sensor has achieved the required temperature.
This value equates to an HO2S output of 450 to 500 mV. A richer mixture can be shown as λ = 0.97, this pushes the
HO2S output voltage towards 1000 mV. A leaner mixture can be shown as λ = 1.10, this pushes the HO2S output
voltage towards 100 mV.
From cold start, the ECM runs an open loop fuelling strategy. The ECM keeps this strategy in place until the HO2S is
at a working temperature of 350 °C (662 °F). At this point the ECM starts to receive HO2S information and it can then
switch into closed loop fuelling as part of its adaptive strategy. The maximum working temperature of the tip of the
HO2S is 930 °C (1706 °F), temperatures above this will damage the sensor.
HO2S age with use, this increases their response time to switch from rich to lean and from lean to rich. This can lead
to increased exhaust emissions over a period of time. The switching time of the upstream sensors are monitored by
the ECM. If a pre-determined threshold is exceeded, a failure is detected and the MIL illuminated.
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EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Exhaust Emission Control System.
Input/Output
The upstream and downstream HO2S are colour coded to prevent incorrect fitting. The tips of the upstream sensors
are physically different to the tips of the downstream sensors.
The HO2S are colour coded as follows:
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Upstream sensors (both banks) - orange.
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Downstream sensors (both banks) - grey.
The four HO2S have a direct battery supply to the heater via fuse 2 located in the engine compartment fuse box.
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DESCRIPTION AND OPERATION
| Categories | Land Rover Defender, Land Rover Discovery II, Range Rover |
|---|---|
| Tags | Land Rover |
| Model Year | 1999 |
| Download File |
|
| Document Type | Workshop Manual |
| Language | English |
| Product Name | Discovery Series II |
| Product Brand | Land Rover |
| Document File Type | |
| Publisher | landrover.com |
| Wikipedia's Page | http://en.wikipedia.org/wiki/Land_Rover |
| Copyright | Attribution Non-commercial |
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