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Home >> BMW >> 1990 >> 735i >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Trouble Code Diagnosis >> Trouble Code 45 (Fault Code 3) >> Coolant Temperature Sensor
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Coolant Temperature Sensor

  1. Disconnect coolant temperature sensor. Turn ignition switch to RUN position. Check for 5 volts between Brown/Red wire of harness side connector and ground. If no voltage is present, check continuity of wiring to MCU (in control box at right shock tower).
  2. Check for 5 volts between Brown/Red and Brown/Orange wires of harness side connector. If no voltage is present, check for open or short in Brown/Orange wire to ground.
  3. If voltage was okay, reconnect coolant temperature sensor and erase trouble code from MCU memory. Test drive vehicle and recheck for trouble code. If no code present, problem may be intermittent. See INTERMITTENTS in TESTS W/O CODES article.
  4. If code is still present, replace coolant temperature sensor. Ensure resistance of coolant temperature sensor is 2300-2700 ohms at 72°F (20°C) and 300-360 ohms at 186°F (80°C). Erase trouble code from MCU memory. Test drive vehicle and recheck for trouble code. If code still present, replace MCU with a known good unit.
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