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.
Field Service Mode Check
This test confirms proper fuel system operation and verifies closed loop operation. Clear codes and perform this test after any repair is completed. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on FWD models does NOT hold drive wheels.
1) Start engine. With engine running, ground test terminal "B" of the ALDL. In closed loop mode, SERVICE ENGINE SOON light will flash at a rate of one flash per second.
2) In open loop, light will flash at a rate of 2.5 flashes per second. If light is off most of the time, a lean exhaust is indicated. If light is on most of the time, a rich exhaust is indicated.
NO RELATED
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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.