OPERATION
The engine control relay connector terminal supplies power to the heater power terminal on the oxygen sensor (rear) connector.
The power transistor in the engine-ECU connection terminal OHRL controls the heater of the oxygen sensor (rear) connector terminal.
Capability
The engine-power ECU’s transistor’s ON/OFF switch controls the power supply to the oxygen sensor (rear) heater.
By heating the oxygen sensor (rear) heater, it is possible for the oxygen sensor (rear) to respond accurately even when the temperature of the exhaust emission is low.
Inconvenience Judgment
Check Conditions: The electric motor switch’s power supply mode has been ON for more than 2 seconds.
When the rear heater for the oxygen sensor is on, the accessory battery’s positive voltage must be greater than 11 V but not greater than 16.5 V.
Criterion: For two seconds, the oxygen sensor’s (rear) heater current is less than 0.17 A.
Check Conditions: The electric motor switch’s power supply mode has been ON for more than 2 seconds.
The positive voltage of the auxiliary battery must be greater than 11 V and less than 16.5 V while the oxygen sensor heater (rear) is off.
Criterion: For two seconds, the oxygen sensor (rear) heater voltage is less than 2.0 V.
Possible Fault
Faulty oxygen sensor (rear) heater
Open/short circuit or harness damage in oxygen sensor (rear) heater circuit or loose connector contact
Faulty engine-ECU
Checking Procedure
Resistance measurement at the oxygen sensor (rear) connector:
Oxygen sensor (rear) connector check.
Unplug the connector, and measure at the sensor side.
The resistance between the terminal power supply line and engine-ECU OHRL line.
4.5 – 8.0 Ω at 20°C is ok
If not Repair or replace the connector, or replace the oxygen sensor (rear).
Voltage measurement at oxygen sensor (rear) connector:
Unplug connector, and measure at the harness side
Power supply mode of electric motor switch: ON
The voltage between the terminal power supply line and the body earth.
If not right: Between the oxygen sensor (rear) connector terminal and the engine control relay connector terminal, repair or replace the connector, or inspect and repair the harness.
Check for open or short circuits in the power supply line.Voltage measurement at engine-ECU connector:
Unplug connector, and measure at harness side.
Power supply mode of electric motor switch: ON
Voltage between terminal OHRL and body earth.
If not right:
The connector, or the harness connecting the oxygen sensor (rear) connector terminal and the engine-ECU connector terminal, should be repaired or replaced.
Examine the earthing line for any shorts or opens.Check harness between oxygen sensor (rear) connector terminal and engine-ECU connector terminal OHRL.
Check earthing line for damage.
If not: Repair or replace the connector, or repair the damaged harness wire.
Check harness between oxygen sensor (rear) connector terminal and engine control relay connector terminal.
Check power supply line for damage.
Intermittent malfunctions:
Cautiously shake or move the connector up, down and to the left and right.
Cautiously shake or move the wiring harness up, down and to the left and right.
Cautiously rock each sensor and relay, etc. by hand.
Cautiously shake or move the wiring harness at suspensions and other moving parts.
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