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Code 3, Coolant Temperature Sensor
- Turn ignition to "OFF" position. Unplug CIS-E control unit connector. Check resistance between sockets No. 7 and No. 21. Resistance reading should be as indicated in table. See Fig 1
. If not okay, check wiring.
- Unplug coolant temperature sensor connector. Measure resistance between any 2 of the diagonally opposed terminals and compare resistance values from each internal sensor. Resistance reading should be as indicated in table. See Fig 1
. If not okay, replace sensor.
- Check wiring harness continuity to CIS-E control unit. Resistance should be less than one ohm. If not okay, check for open circuit.
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.