Start engine and warm it up to the normal operating temperature.
Turn ignition switch OFF and wait at least 10 seconds.
Start engine and keep the engine speed between 3,500 and 4,000 RPM for 1 minute under no load.
Let engine idle for 1 minute.
Set voltmeters probes between ECM terminals 114 [HO2S1 (bank 1) signal], 115 [HO2S1 (bank 2) signal] and ground, and ECM terminals 123 [HO2S2 (bank 1) signal], 124 [HO2S2 (bank 2) signal] and ground. See Figure and Figure .
Keep engine speed at 2,000 RPM constant under no load.
Make sure that the voltage switching frequency (high & low) between ECM terminals 123 and ground, or 124 and ground is very less than that of ECM terminals 114 and ground, or 115 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 does not operate properly. Go to Diagnostic Procedure .

NOTE: If the voltage at terminal 114 or 115 does not switch periodically more than 5 times within 10 seconds at step 5, perform trouble diagnosis for "DTC P0133, P0153" first. (See DTC P0133, P0153 HO2S1 .)

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

With GST

Use the Manual With the Right Hardware

When to See a Mechanic

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