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.
Federal 2WD Models
Secondary (fresh) air drawn from the air cleaner is supplied to the exhaust ports of both cylinder heads. Also, a constant supply of secondary air is supplied to the exhaust port near the upstream portion of oxidation catalyst by ASV (rear). The ASV (rear) is mounted on the exhaust pipe and uses no cut-off valve. See Fig 1 .
The ASV's (Front) are equipped with cut-off valves which are controlled by the thermosensor, which senses coolant temperature, and time controlled by the ECM.
When coolant temperature is below 95°F (35°C), the ECM gives a command to open intake manifold vacuum passage of solenoid valve for a period of 123 seconds. The cut-off valve vacuum diaphragm is opened and ASV operation begins.
Under certain driving conditions, such as wide open throttle acceleration, check valve is closed which confines vacuum and opens the cut-off valve for air injection operation. This operation is provided for the control of exhaust emissions.
After coolant temperature is above 95°F (35°C) and/or 123 seconds have passed, the ECM gives a command to close the vacuum passage of the solenoid valve. Vacuum is then bled off to atmosphere and the cut-off valve is closed, deactivating ASV system.
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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.
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