Discovery II (LT) V8-4.0L (2002)
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Upstream RH bank via pin 16 of connector C0635 of the ECM.
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Downstream LH bank via pin 17 of connector C0635 of the ECM.
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Downstream RH bank via pin 14 of connector C0635 of the ECM.
The HO2S earth path for the signal is supplied by the ECM as follows:
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Upstream LH bank via pin 9 of connector C0635 of the ECM.
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Upstream RH bank via pin 10 of connector C0635 of the ECM.
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Downstream LH bank via pin 11 of connector C0635 of the ECM.
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Downstream RH bank via pin 8 of connector C0635 of the ECM.
The HO2S voltage is difficult to measure using a multimeter, the output can be monitored using TestBook. A rich mixture would read 500 to 1000
mV, a weak mixture would read 100 mV to 500 mV, the reading should switch from rich to weak. The open loop default voltage is 450 mV, this is
used by the ECM to set the air/fuel ratio until the tip of the HO2S reaches operating temperature.
The HO2S can fail the following ways or supply incorrect signal:
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Sensor open circuit.
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Short circuit to vehicle supply.
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Short circuit to vehicle earth.
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Sensor disconnected.
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Stoichiometric ratio outside the correct operating band.
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Contamination from leaded fuel.
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Air leak into the exhaust system.
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Wiring loom damage.
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Sensors fitted incorrectly or cross wired.
In the event of a HO2S signal failure any of the following symptoms may be observed:
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Default to open loop fuelling on defective bank.
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If the sensors are crossed over (LH bank to RH bank), the engine will run normally after initial start up, but performance will become
progressively worse as the sensors go towards maximum rich for one bank of cylinders and maximum lean for the other. The ECM will
eventually default into open loop fuelling.
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High CO reading.
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Excess emissions.
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Strong hydrogen sulphide (H2S) smell until the ECM defaults to open loop fuelling.
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MIL illuminated (NAS market only).
A number of diagnostic tests are performed by the ECM with regards to the HO2sensors:
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HO2 sensor and system diagnostics
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HO2 sensor heater diagnostics
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HO2 sensor switching period (ageing) diagnostics
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Rear HO2 sensor adaption diagnostic (NAS only)
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Catalyst monitoring diagnostic
Should a malfunction of the component occur the following fault codes may be evident and can be retrieved by TestBook:
