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.
The ignition switch supplies battery voltage to the ECU. A voltage protection relay prevents current surges from damaging the ECU.
The ECU unit utilizes various input signals to control fuel delivery and exhaust emissions. Input signals control output current to the differential pressure regulator, and 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.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.