With GST

1. Turn ignition switch OFF and wait at least 10 seconds.
2. Start engine and keep the engine speed between 3, 500 and 4, 000 RPM for at least 1 minute under no load.
3. Let engine idle for 1 minute.
4. Open engine hood.
5. Set voltmeters probes between ECM terminals 35 [HO2S1 (bank 1) signal], 16 [HO2S1 (bank 2) signal] and ground, and ECM terminals 74 [HO2S2 (bank 1) signal], 55 [HO2S2 (bank 2) signal] and ground.
   Fig 1: Checking Voltage Between ECM Terminals 35, 16 And Ground

   Courtesy of NISSAN MOTOR CO., U.S.A.
6. Keep engine speed at 2, 000 RPM constant under no load.
7. Make sure that the voltage switching frequency (high & low) between ECM terminals 74 and ground, or 55 and ground is very less than that of ECM terminals 35 and ground, or 16 and ground.

Switching frequency ratio = A/B 

A: Heated oxygen sensor 2 voltage switching frequency 

B: Heated oxygen sensor 1 voltage switching frequency 

This ratio should be less than 0.75. 

If the ratio is greater than above, it means three way catalyst 1 does not operate properly. Go to Diagnostic Procedure .

Fig 2: Checking Voltage Between ECM Terminals 55, 74 And Ground

Courtesy of NISSAN MOTOR CO., U.S.A.