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.
"Scan" Diagnostic Circuit Check
The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an assembly line communication link (ALCL). This communication link can provide diagnostic information for display on any "SCAN" device or tool designed for this purpose.
- If the "SCAN" tool is not operating, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. If the "SCAN" tool reads "no data" or "no ALCL", with the ignition "ON", check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line should have a varying 2-5 volts and the diagnostic line about 5 volts.
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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.