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
Coolant Temperature Sensor
- Disconnect plug from coolant temperature sensor. Using ohmmeter, check resistance between sensor terminal and ground. Measure resistance at 2 different temperatures. If readings are not correct, replace coolant temperature sensor. If coolant temperature sensor is good, go to next step.
- Connect meter adapter cable between differential pressure regulator and multimeter. Set meter to mA scale. Disconnect wire to O2 sensor. Turn ignition on and check current reading. At operating temperature, reading should be 7-9 mA.
- At coolant temperature of 60°F (20°C), reading should be 9-14 mA. If wiring to temperature sensor is disconnected, reading should be 114-132 mA. If readings are correct, unit is okay and test is completed. If readings are not correct, go to next step.
- Disconnect plug to differential pressure regulator. Resistance reading of regulator should be 18-21 ohms. If reading is not in range, replace differential pressure regulator. If reading is good, go to next step.
- Check voltage at plug connector for coolant temperature sensor. Voltage should be 5 volts. If there is no voltage, repair wiring. If voltage is correct, go to next step.
- Check wiring between ECU and differential pressure regulator for continuity. If continuity tests good, replace ECU. If no continuity, repair short in wiring.
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.