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Pinpoint Test L: In-Vehicle Temperature And Humidity Sensor Not Operating Properly - Flash Code 4020, 4021

  1. Refer to Automatic Climate Control System for schematic and connector information.

    Normal Operation and Fault Conditions 

    Refer to the In-Vehicle Temperature and Humidity Sensor. REFER to: Climate Control System - System Operation and Component Description  .

    HVAC Flash Codes 

    • FLASH CODE 4020: CABIN AIR TEMPERATURE SENSOR OUT OF RANGE.
    • FLASH CODE 4021: CABIN AIR TEMPERATURE SENSOR DISCONNECTED.

    Possible Sources 

    • Wiring, terminals or connectors
    • In-vehicle temperature and humidity sensor
    • HVAC control module

    Visual Inspection and Pre-checks 

    • Verify BCM fuse 21 (5A) is ok.

  2. NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may cause damage to the connector.

  3. L1 CHECK THE HVAC (HEATING, VENTILATION AND AIR CONDITIONING) CONTROL MODULE FOR FLASH CODES

    NOTE: Diagnostic flash codes are 4 digit codes communicated via a blinking LED located near the connectors on the HVAC control module.

    • Ignition OFF. Wait 10 seconds.

    • Ignition ON.

    • Check the HVAC control module LED for Flash codes.

    Is Flash Code 4020 or 4021 present? 

    Yes  For flash code 4020, GO to  L2 For flash code 4021, GO to  L6
    No  The concern may have been caused high network traffic or an intermittent fault condition. DIAGNOSE any other Flash Codes or Symptoms. REFER to HVAC Control Module Diagnostic Flash Codes  or Symptom Charts .

  4. L2 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR RESISTANCE - FLASH CODE 4020

    • Ignition OFF.

    • Disconnect HVAC control module C228A.

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C228A-20
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 C228A-21

    Is the resistance between 3000 ohms and 270, 000 ohms? 

    Yes  GO to  L3
    No  GO to  L4

  5. L3 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR FOR A SHORT TO GROUND - FLASH CODE 4020

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C228A-20
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is the resistance greater than 10, 000 ohms? 

    Yes  GO to  L10
    No  GO to  L4

  6. L4 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR CIRCUITS FOR A SHORT TOGETHER - FLASH CODE 4020

    • Ignition OFF.

    • Disconnect In-vehicle temperature and humidity sensor C233.

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C228A-20
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 C228A-21

    Is the resistance greater than 10, 000 ohms? 

    Yes  GO to  L5
    No  REPAIR the circuits.

  7. L5 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR CIRCUITS FOR A SHORT TO GROUND - FLASH CODE 4020

    • Ignition OFF.

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C228A-20
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 Ground
      C228A-21
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 Ground

    Are the resistances greater than 10, 000 ohms? 

    Yes  INSTALL a new in-vehicle temperature and humidity sensor. REFER to: In-Vehicle Temperature and Humidity Sensor  . TEST the system for normal operation. If the concern is still present, GO to  L10
    No  REPAIR the affected circuit.

  8. L6 CHECK THE HVAC (HEATING, VENTILATION AND AIR CONDITIONING) CONTROL MODULE CONNECTOR PINS - FLASH CODE 4021

    • Ignition OFF.

    • Disconnect HVAC control module C228A.

    • Inspect and repair pins 20 and 21:

      • corrosion (install new connector or terminal - clean module pins)
      • damaged or bent pins - install new terminals or pins
      • pushed-out pins - install new pins as necessary

    • Connect HVAC control module C228A. Make sure it seats and latches correctly.

    • Operate the system and determine if the concern is still present.

    Is the concern still present? 

    Yes  GO to  L7
    No  The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues.

  9. L7 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR RESISTANCE - FLASH CODE 4021

    NOTE: Ignore if Cabin Temperature is less than -10°C (14°F).

    • Ignition OFF.

    • Disconnect HVAC control module C228A.

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C228A-20
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 C228A-21

    Is the resistance between 3000 ohms and 270, 000 ohms? 

    Yes  GO to  L10
    No  GO to  L8

  10. L8 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR CONNECTOR PINS - FLASH CODE 4021

    NOTE: Check Connector, C233, for disconnect or damage.

    • Disconnect In-vehicle temperature and humidity sensor C233.

    • Inspect and repair pins 2 and 5:

      • corrosion (install new connector or terminal - clean module pins)
      • damaged or bent pins - install new terminals or pins
      • pushed-out pins - install new pins as necessary

    • Connect In-vehicle temperature and humidity sensor C233. Make sure it seats and latches correctly.

    • Operate the system and determine if the concern is still present.

    Is the concern still present? 

    Yes  GO to  L9
    No  The system is operating correctly at this time. The concern may have been caused by sensor connections. ADDRESS the root cause of any connector or pin issues.

  11. L9 CHECK THE IN-VEHICLE TEMPERATURE AND HUMIDITY SENSOR CIRCUITS FOR AN OPEN - FLASH CODE 4021

    • Ignition OFF.

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C228A-20
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 C233-2
      C228A-21
      GFD345528Courtesy of FORD MOTOR COMPANY
      		 C233-5

    Are the resistances less than 3 ohms? 

    Yes  INSTALL a new in-vehicle temperature and humidity sensor. REFER to: In-Vehicle Temperature and Humidity Sensor  . TEST the system for normal operation. If the concern is still present, GO to  L10
    No  REPAIR the affected circuit.

  12. L10 CHECK FOR CORRECT HVAC (HEATING, VENTILATION AND AIR CONDITIONING) CONTROL MODULE OPERATION

    • Ignition OFF.

    • Disconnect and inspect all HVAC control module electrical connectors (if not previously disconnected).

    • Repair:

      • corrosion (install new connector or terminal - clean module pins)
      • damaged or bent pins - install new terminals or pins
      • pushed-out pins - install new pins as necessary

    • Connect all HVAC control module electrical connectors. Make sure they seat and latch correctly.

    • Operate the system and determine if the concern is still present.

    Is the concern still present? 

    Yes  CHECK OASIS for any applicable service articles: TSB, GSB, SSM or FSA. If a service article exists for this concern, DISCONTINUE this test and FOLLOW the service article instructions. If no service articles address this concern, INSTALL a new HVAC control module. Refer to Heating, Ventilation and Air Conditioning (HVAC) Control Module .
    No  The system is operating correctly at this time. The concern may have been caused by module connections. ADDRESS the root cause of any connector or pin issues.
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