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.
Electronic Control Unit (Ecu)
On 420 and 560 sedan models the ECU is located behind the right kick panel on the passenger side. On 560 SL models the ECU is located under the right kick panel on the passenger side.
With ignition switched on, the ECU is connected to battery voltage. To prevent voltage fluctuations when vehicle components are switched on, the ECU is provided with a voltage protection relay.
The ECU unit utilizes various input signals for control of fuel delivery and exhaust emissions. Input signals are converted into corresponding current values and are sent to the differential pressure regulator and to idle speed air valve.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.