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Pinpoint Test E: DTC B1255 Or B1257

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
  1. E1 CHECK THE AMBIENT TEMPERATURE SENSOR RESISTANCE 
    • Key in OFF position.
    • Disconnect: Ambient Temperature Sensor C132
      • Fig 1: Measuring Resistance
      GF0007897Courtesy of FORD MOTOR CO.
    • Measure the resistance between the ambient temperature sensor terminals.
    • Is the resistance within the specified values for these temperature ranges: 10-20°C (50-68°F), 37,000-58,000 ohms; 20-30°C (68-86°F), 24,000-37,000 ohms; 30-40°C (86-104°F), 16,000-24,000 ohms? 
    1. YES  : Go to  E2.
    2. NO  : INSTALL a new ambient air temperature sensor and bracket. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  2. E2 CHECK THE HVAC MODULE OUTPUT VOLTAGE 
    • Key in ON position.
    • Press the AUTOMATIC button.
      • Fig 2: Checking EATC Module Output Voltage
      GF0014307Courtesy of FORD MOTOR CO.
    • Measure the voltage between ambient temperature sensor C132-1, circuit 3061 (LB/OG), harness side and C132-2, circuit 3059 (YE/LG), harness side.
    • Is the voltage between 4.7 and 5.1 volts? 
    1. YES  : INSTALL a new ambient air temperature sensor. TEST the system for normal operation. If the code returns, go to  E7.
    2. NO  : If diagnosing DTC B1255  , go to  E3.

      If diagnosing DTC B1257  , go to  E5.

  3. E3 CHECK CIRCUIT 3061 (LB/OG) FOR AN OPEN 
    • Key in OFF position.
    • Disconnect: HVAC Module C228a
      • Fig 3: Measuring Resistance
      GF0047628Courtesy of FORD MOTOR CO.
    • Measure the resistance between HVAC module C228b-17, circuit 3061 (LB/OG), harness side and ambient temperature sensor C132-1, circuit 3061 (LB/OG), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  E4.
    2. NO  : REPAIR circuit 3061 (LB/OG) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  4. E4 CHECK CIRCUIT 3059 (YE/LG) FOR AN OPEN 
      Fig 4: Measuring Resistance
      GF0047629Courtesy of FORD MOTOR CO.
    • Measure the resistance between HVAC module C228b-16, circuit 3059 (YE/LG), harness side and ambient temperature sensor C132-2, circuit 3059 (YE/LG), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  E7.
    2. NO  : REPAIR circuit 3059 (YE/LG) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  5. E5 CHECK CIRCUIT 3061 (LB/OG) FOR A SHORT TO CIRCUIT 3059 (YE/LG) 
    • Key in OFF position.
    • Disconnect: HVAC Module C228a
    • Disconnect: HVAC Module C228b
    • Measure the resistance between ambient temperature sensor C132-1, circuit 3061 (LB/OG), harness side and C132-2, circuit 3059 (YE/LG), harness side.
    • Is the resistance greater than 10,000 ohms? 
    1. YES  : Go to  E6.
    2. NO  : REPAIR circuit 3061 (LB/OG) for a short to circuit 3059 (YE/LG). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  6. E6 CHECK CIRCUIT 3061 (LB/OG) FOR A SHORT TO GROUND 
      Fig 5: Measuring Resistance
      GF0047630Courtesy of FORD MOTOR CO.
    • Measure the resistance between HVAC module C228-17, circuit 3061 (LB/OG), harness side and ground.
    • Is the resistance greater than 10,000 ohms? 
    1. YES  : Go to  E7.
    2. NO  : REPAIR circuit 3061 (LB/OG) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  7. E7 CHECK HVAC MODULE CONNECTION 
    1. YES  : INSTALL a new HVAC module. REFER to CLIMATE CONTROL article. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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