DTC B1255/B1257 Test: Ambient Temperature Sensor Circuit Open Or Shorted

WARNING: This page is about a different car, the 1999 Lincoln Navigator and 1999 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

Check Ambient Temperature Sensor Resistance

Turn ignition off. Disconnect ambient temperature sensor connector, 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 retest system.

Check Ambient Temperature Sensor Output Voltage

Turn ignition to run position (engine off). Press AUTOMATIC button on EATC panel. With a voltmeter, measure voltage of ambient temperature sensor. If voltage is between 4.7 and 5.1 volts, go to step 6) . If voltage is not as specified, go to next step.

Check Light Blue/Orange Wire Circuit For Open

Turn ignition off. Disconnect EATC module connector C280. With an ohmmeter, measure resistance of Light Blue/Orange wire between EATC module connector C280 and ambient temperature sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair open in Light Blue/Orange wire and retest system.

Check Light Blue/Orange Wire For Short To Ground

Turn ignition off. Disconnect EATC module C280 connector. Measure resistance of Light Blue/Orange wire between EATC module connector and ground. If resistance is more than 10,000 ohms, replace EATC module. Retest system. If resistance is less than 10,000 ohms, repair short to ground in Light Blue/Orange wire. Retest system.

Check Pink/Black Wire Circuit For Open

Measure resistance of Pink/Black wire between EATC module connector C280 and ambient temperature sensor connector. If resistance is less than 5 ohms, replace EATC module and retest system. If resistance is more than 5 ohms, repair open in Pink/Black wire and retest system.

Check Ambient Temperature Sensor Connections

Disconnect EATC module connector C280. Inspect ambient temperature sensor connector pins, and pins of EATC connector C280 Pink/Black and Light Blue/Orange wires for damage, loose fit or improper installation. If all wiring is undamaged and properly connected, replace EATC module and retest system. If wiring shows signs of damage or incorrect connections, repair wiring as needed and retest system.