DTC B1251/B1253 Test: In-Car 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.

Inspect Connectors

Turn ignition off. Disconnect both EATC module connectors. Disconnect in-car temperature sensor connector, located under top center of instrument panel. Inspect all connector pins for damage, loose fit or incorrect installation. If all connectors are okay, go to next step. If any connector is faulty, repair problem connector. Retest system.

Check In-Car Temperature Sensor Resistance

Turn ignition off. Reconnect both EATC module connectors. With an ohmmeter, measure resistance between terminals of in-car temperature sensor. See TEMPERATURE SENSOR RESISTANCE TEST table. If resistance is within specifications, go to next step. If resistance is not within specifications, replace in-car temperature sensor. Retest system.

TEMPERATURE SENSOR RESISTANCE TEST

Temperature °F (°C)	Ohms
50-68 (10-20)	37,000-58,000
68-86 (20-30)	24,000-37,000
86-104 (30-40)	16,000-24,000

Check EATC Sensor Output Voltage

Turn ignition to run position (engine off). Press AUTOMATIC button on EATC panel. With a voltmeter, measure voltage between in-car temperature sensor connector White/Orange wire and Pink/Black wire. If voltage is between 4.7 and 5.1 volts, go to step 5) . If voltage is not as specified, go to next step.

Check White/Orange Wire Circuit For Open

Turn ignition off. Disconnect EATC module connector (C281). With an ohmmeter, measure resistance of White/Orange wire between EATC module connector and in-car temperature sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair open in White/Orange wire and retest system.

Check White/Orange Wire For Short To Ground

Turn ignition off. Disconnect EATC module connector (C281). Measure resistance of White/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 White/Orange wire. Retest system.

Check Pink/Black Wire Circuit For Open

Disconnect EATC module connector C280. With an ohmmeter, measure resistance of Pink/Black wire between connector C280 and in-car 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.