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
Lambda Control (Federal)
- Connect On-Off Ratio Tester (KDJE-P 600) to diagnostic socket located on left fenderwell. Run engine until operating temperature is reached. If any malfunction codes are present, they must be repaired first before testing Lambda control. Unplug oxygen sensor connector located under carpet in front of passenger seat. Read and record voltage on tester with engine idling. Reconnect O[I2] sensor connector. Push 12-volt button on tester.
- Set engine speed to 2000 RPM. If engine is at operating temperature, voltage reading should not vary from previously recorded voltage by more than 0.8 volt. If reading is correct, lambda control is working and test is complete. If reading is incorrect, see Test Step No. 14 for 6-cylinder engines and see Test Steps No. 3 and 9 for V8 engines under TESTS W/CODES article in this section.
Factory Service Tools
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.