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.
1991 Mercedes Benz 560SECFACTORY OEM SERVICE PROCEDURE
On-Board Diagnostics Using Mas Unit Memory
- When engine is running and a fault occurs, any fault codes or malfunctions are also stored in MAS unit memory as well as CIS-E control unit memory.
- On 190E Series and 300 Series except 300SE and 300SEL, MAS unit codes can be read using impulse counter connected directly to diagnostic connector pin sockets No. 1 and No. 14.
- On 300SE and 300SEL, MAS unit codes can ONLY be read using socket box tester connected between MAS unit and MAS unit connector socket. Connect Black impulse counter lead to diagnostic connector pin socket No. 4. Connect Yellow lead to socket box tester pin socket No. 14.
Factory Service Tools
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.