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.
Control Units
The Ignition Control Unit (ICU) collects signals from the altitude sensor, ignition distributor, knock sensor, temperature sensor, throttle valve switches and the fuel injection control unit. Using the collected data, it continuously updates the required degree of ignition advance/retard.
There are 2 separate ignition timing maps programmed into the ICU. One is programmed for regular fuel. The other is programmed for premium fuel.
When the coolant temperature reaches 149°F (65°C), the ICU automatically switches to the premium fuel map. The premium fuel map is programmed to have timing with a slightly advanced curve in some of the lower RPM ranges.
If ignition knock occurs repeatedly, the ICU will automatically switch to the regular fuel map. The ICU will switch back to the premium fuel map after a fixed amount of time or whenever the engine is restarted.
The Fuel Injection Control Unit (FICU) receives signals from the air sensor potentiometer, altitude sensor, oxygen sensor, temperature sensor, throttle valve switches and the ignition control unit. Using this data, it varies the air fuel mixture as necessary.
Both control units constantly interface with each other. Each control unit contains it's own fault memory. During self-diagnosis the ignition control unit will always display it's fault codes first. The fuel injection control unit will then display it's fault codes.
The FICU is in a slide-in bracket located behind the right kick panel. See Figure . The ICU is bolted to a bracket located behind the left kick panel. See Figure .
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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.