(a) Connect an intelligent tester to the DLC3.

(b) Start the engine and warm it up with all the accessories switched OFF, until the engine coolant temperature stabilizes.

(c) Run the engine at an engine speed of between 2,500 rpm and 3,000 rpm for at least 3 minutes.

(d) While running the engine at 3,000 rpm for 2 seconds and 2,000 rpm for 2 seconds, check the waveforms of the A/F and HO2 sensors using the tester (refer to Conditioning for Sensor Testing).


• If either of the voltage outputs of the Air-Fuel Ratio (A/F) or Heated Oxygen (HO2) sensor does not fluctuate, or either of the sensors makes a noise, the sensor may be malfunctioning.

• If the voltage outputs of both the sensors remain lean or rich, the air-fuel ratio may be extremely lean or rich. In such cases, perform the following A/F CONTROL using an intelligent tester.

• If the Three-Way Catalytic Converter (TWC) has deteriorated, the HO2 sensor (located behind the TWC) voltage output fluctuates up and down frequently, even under normal driving conditions (active air-fuel ratio control is not performed).

Voltage output when active air-fuel ratio control not performed

Normal Catalyst

Waveform of A/F Sensor in 35 V front of TWC

Deteriorated Catalyst

Waveform of HO2 Sensor behind TWC

10 seconds

10 seconds


Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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