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.
Test Description
The number below refer to the step number on the diagnostic procedure.
- 2
O2S contamination is indicated if multiple response, switching, or time ratio O2S DTCs are set. - 4
The use of leaded fuel may be indicated by evidence of the removal or tampering of the fuel filter restrictor.An O2S contaminated by silicone will have a White, powdery deposit on the portion of the O2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of an unapproved silicone RTV engine gasket material, or the use of silicone-based sprays or fluids within the engine.
If the cause of this contamination is not corrected, the replacement O2S will also become contaminated.
- 7
Even small exhaust leaks can cause slow response from the O2S. - 12
An O2S contaminated by silicone will have a White, powdery deposit on the portion of the O2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of an unapproved silicone RTV engine gasket material or the use of the use of silicone-based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement O2S will also become contaminated. - 13
If the voltage observed in step 8 is less than the range specified, a short between the HIGH and LOW signal circuits or a short between the HIGH signal circuit and ground is indicated. With the O2S, AF ECM and the PCM disconnected the resistance between the HIGH and LOW signal circuits and the resistance between the HIGH signal circuit and ground should measure infinite.If the voltage observed in step 8 is more than the range specified, a short between the HIGH signal circuit and an ignition voltage source is indicated.
- 14
If the voltage observed in step 9 is not less than the voltage specified, a high resistance or open, HIGH or LOW circuit is indicated.Good circuit continuity measures less than 5 ohms with AF ECM, PCM and sensor disconnected. Measure between the PCM connector and O2S connector. Ensure PCM terminal contact is good.
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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.