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.

1994 GMC Forward Control 7.4 NFACTORY OEM SERVICE PROCEDURE

Diagnostic Aids

Code 43 can be caused by a faulty knock sensor connection at ESC module or ECM. Also, check controller-to-ECM signal line for an open or short to ground.

Fig 1: Code 43 Schematic ("C" & "K" Series) Knock Sensor W/ Spark Control Module

Factory Service Tools

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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