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 16 - OPTI-Spark Ignition System - Low Resolution Pulse: Notes
Ignition system supplies 2 timing inputs to ECM, a high resolution signal (360 pulses per camshaft revolution) and a low resolution signal (8 pulses per camshaft revolution). ECM can determine if either timing input is not being received by comparing inputs. If ECM detects high resolution pulse without detecting low pulse, Code 16 will set. Reference signal on resolution line toggles between zero and 5 volts as camshaft turns.
- Code 16 will set if 720 high resolution timing pulses occur before any low resolution pulses are detected.
- This step determines if ECM is sending out a signal to distributor for processing. If this signal is not available or is shorted to ground or voltage, distributor cannot ground it to produce reference pulses.
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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.