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Home >> Ford >> 2002 >> Crown Victoria Base, 4.6 9 >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> HVAC System - Automatic >> Self-Diagnostics >> DTC B1255/B1257 Test: Ambient Temperature Sensor Circuit Inoperative

DTC B1255/B1257 Test: Ambient Temperature Sensor Circuit Inoperative

  1. Turn ignition off. Disconnect ambient temperature sensor 2-pin harness connector C160, located below upper radiator support. Measure resistance between in-car temperature sensor terminals. See TEMPERATURE SENSOR RESISTANCE TEST  table. If resistance is within specifications, go to next step. If resistance is not within specifications, replace ambient temperature sensor and bracket. Recheck system operation.
  2. Turn ignition on. Press AUTO button on EATC panel. Measure voltage between ambient temperature sensor harness connector Light Blue/Orange wire and Pink/Black wire terminals. If 4.7-5.1 volts exists, go to step  6. If voltage is not as specified, go to next step.
  3. Turn ignition off. Disconnect EATC module 13-pin harness connector C227. Disconnect ambient air temperature sensor 2-pin harness connector C160. Measure resistance of Light Blue/Orange wire between EATC module harness connector C227 terminal No. 7 and ambient temperature sensor harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open or high resistance in Light Blue/Orange wire. See WIRING DIAGRAMS . Recheck system operation.
  4. Turn ignition off. Measure resistance between ground and EATC module harness connector C227 terminal No. 7 (Light Blue/Orange wire). If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in Light Blue/Orange wire between ambient air temperature sensor and EATC module. See WIRING DIAGRAMS . Recheck system operation.
  5. Measure resistance of Pink/Black wire between EATC module harness connector C227 terminal No. 4 and ambient temperature sensor harness connector. If resistance is less than 5 ohms, replace EATC module. Recheck system operation. If resistance is 5 ohms or more, repair open or high resistance in Pink/Black wire. See WIRING DIAGRAMS . Recheck system operation.
  6. Disconnect EATC module harness connector C227. Inspect ambient temperature sensor and EATC connector terminals for damage, loose fit or improper installation. If all wiring and connector terminals are undamaged and properly connected, replace EATC module. Recheck system operation. If wiring shows signs of damage or improper connections, repair appropriate wiring as needed. See WIRING DIAGRAMS . Recheck system operation.
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