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.
Chart A-1, No Mil (Service Engine Soon Light) 4L80-E W/ TCM: Notes
MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The TCM turns light on by providing a ground path through the MIL (SERVICE ENGINE SOON) control circuit.
- If ECM-BAT fuse is blown, see WIRING DIAGRAMS at the end of this article for complete circuit.
- Using a test light connected to 12 volts, probe each of the system ground circuits to ensure a good ground is present. See PIN VOLTAGE CHARTS - 6.5L DIESEL article.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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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