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.
Main Relay Control
The MS S52 control module activates the main relay when KL 15 is switched ON. This provides operating power for the control module and in addition the following systems/circuits also receive operating power from the main relay:
- Traction control module
- Fuel pump relay
- Secondary air pump relay/air pump
- E-box cooling fan
- Auxiliary oil pump solenoids
- Purge valve
- Fuel injectors
- VANOS solenoids
- Oxygen sensor heaters
- Air mass sensors
- Idle control valve
The MS S52 maintains the ground for the main relay for a short duration after the ignition has been switched off. This allows the control module to store the adoption values and any fault codes.
Use the Manual With the Right Hardware
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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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