Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Overall Function Check
Use this procedure to check the overall function of the three way catalyst. During this check, a 1st trip DTC might not be confirmed.
WITH GST
- Start engine and warm it up to the normal operating temperature.
- Turn ignition switch OFF and wait at least 5 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 50 (Heated oxygen sensor 1 signal), 56 (Heated oxygen sensor 2 signal) and engine ground.
- Keep engine speed at 2,000 RPM constant under no load.
- Make sure that the voltage switching frequency (high & low) between ECM terminal 56 and engine ground is much less than that of ECM terminal 50 and engine 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 (manifold) does not operate properly.
Go to DIAGNOSTIC PROCEDURE .
Use the Manual With the Right Hardware
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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.