On fuel injected models, "SERVICE ENGINE SOON" light will indicate operational mode of engine if ALDL is grounded while engine is running. In closed loop mode, "SERVICE ENGINE SOON" light will flash at a rate of one flash per second. In open loop, light will flash at a rate of 2.5 flashes per second. If light is off all or most of the time, a lean exhaust is indicated. If light is on all or most of the time, a rich exhaust is indicated.

This test confirms proper operation of fuel system 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 front wheel drive models does NOT hold drive wheels.

NOTE: On some engines, oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into open loop. To restore closed loop mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

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

Field Service Mode Check (Fuel Injected Models)

Use the Manual With the Right Hardware

When to See a Mechanic

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