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.
Code P0320, Ignition Control Error - "S" & "T" Series 4.3L (VIN Z): Notes
When system is running on ignition control module, when no voltage is on by-pass line, IC module grounds ignition control signal. Control module expects to sense no voltage on IC line during this condition. If it senses voltage, it sets a code and will not go into IC mode.
When RPM for IC is reached and bypass voltage is applied, IC will no longer be grounded in ignition module, so IC voltage will vary. Control module will disable IC mode if short test fails or default to by-pass mode if long test fails.
- Checks to see if code is an intermittent.
- Checks for a normal IC ground path through module. If IC by-pass wire is shorted to ground, it will also read less than 500 ohms. This will be checked later.
- As test light voltage touches by-pass wire circuit, module should switch, causing ohmmeter to over-range if meter is in 100-200 range. With meter in 10-20,000 range, position will be above 5000 ohms. The important thing is that module switched.
- If module did not switch, this step checks for IC circuit shorted to ground, by-pass circuit open or faulty ignition module or connection.
- This step confirms code is set because of a faulty control module and not an intermittent in circuitry.
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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.