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.
1988 Mercedes Benz 560SLFACTORY OEM SERVICE PROCEDURE
Code 5, Oxygen Sensor
- With engine at operating temperature and at idle, CIS-E control unit connected. Connect voltmeter negative lead socket No. 7 and positive lead to No. 8 of socket box. Voltage should fluctuate between 0.1-0.9 volts. If not, check O2 sensor wiring circuit.
- Disconnect O2 sensor signal connector and ground terminal. Connect voltmeter negative lead to socket No. 7 and O2 sensor signal connector socket. With engine at idle, voltmeter reading should be greater than 450 millivolt. If not, replace O2 sensor.
- Turn ignition "OFF". Unplug CIS-E control unit connector. Connect ohmmeter between socket No. 7 and 8 of socket box. Ohmmeter should read infinity. Connect ohmmeter to socket No. 8 and O2 wiring harness pin. Resistance should be less than one ohm. If not, check for open circuit.
Factory Service Tools
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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.