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.
Switch For Start Control Unit (SCU), Description
The start control unit (SCU) is mounted in the dashboard next to the steering wheel. Besides the cylinder to receive the key, the start control unit (SCU) also contains an antenna cable and four switches. There is one switch for each of the three key positions (I-III) and one to indicate that the key has been inserted into the ignition.
If the keyless vehicle module (KVM) is installed, the key need not be inserted in the ignition where a starter knob is fitted instead. The starter knob must be pressed in before it can be turned from 0 to I and activate the key-in switch. The key identity is checked via the antennae in the passenger compartment that are connected to the keyless vehicle module (KVM).
The ignition's four switches:
- Key-in switch. Also called S-supply switch.
- Ignition X-supply switch.
- Ignition 15-supply switch.
- Ignition 50-supply switch.
Valid key positions
- Key out.
- Key position 0.
- Key position I.
- Key position II.
- Key position II/III. Occurs when key turned from position II to III.
- Key position III.
| Key out | Key Pos 0 | Key Pos I | Key Pos II | Key Pos II / III | Key Pos III | |
| Key in | Not activated | Activated | Activated | Activated | Activated | Activated |
| X-supply | Not activated | Not activated | Activated | Activated | Not activated | Not activated |
| 15 supply | Not activated | Not activated | Not activated | Activated | Activated | Activated |
| 50 supply | Not activated | Not activated | Not activated | Not activated | Not activated | Activated |
NO RELATED
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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.