Ford Fiesta Quiz
Lighting

Exterior Lamps. Diagnosis and Testing

In this manual: Lighting
Service Information — 27Suspension — 48Transmission — 9Brake System — 52Steering — 21Engine — 140Manual Transmission, Clutch, Transfer Case and Power Transfer Unit — 48Exhaust System — 6Fuel System — 21Climate Control System — 58Instrumentation and Warning Systems — 26Battery and Charging System — 20Infotainment Systems — 41Lighting — 29Power Distribution — 11Electronic Function Group — 30Body and Paint — 275Frame and Mounting — 3
~7min read

The diagnosis in this manual assumes a certain level of skill and knowledge of Ford-approved diagnostic procedures.
REFER TO: Diagnostic Methods (100-00 General Information, Description and Operation).

DTC Chart: BCM

DTC Chart


Trouble Code Description Action
B1A85:21 Ambient Light Sensor: Signal Amplitude < Minimum GO to Pinpoint Test B
B1A85:22 Ambient Light Sensor: Signal Amplitude > Maximum GO to Pinpoint Test B

Symptom Chart

The diagnosis in this manual assumes a certain level of skill and knowledge of Ford-approved diagnostic procedures.
REFER TO: Diagnostic Methods (100-00 General Information, Description and Operation).

Symptom Chart: Headlamps

Symptom Chart


Condition Possible Sources Action
Module Does Not Respond to Diagnostic Scan Tool
  • Fuse
  • Wiring, Terminals or Connectors
  • Module
REFER TO: Communication Network (418-00 Communication Network, Diagnosis and Testing).
Exterior lamps inoperative Refer to Pinpoint Test GO to Pinpoint Test A
Exterior lamps always on Refer to Pinpoint Test GO to Pinpoint Test B

Pinpoint Tests

Exterior lamps inoperative


For wiring diagrams and connector information, refer to Section 71 of the Wiring Diagrams.

Normal Operation and Fault Symptoms


REFER to: Exterior Lighting - System Operation and Component Description (417-01 Exterior Lighting, Description and Operation).

Possible Sources

  • Light Sensor
  • Headlight Switch
  • BCM

SPECIFIC TEST A: EXTERIOR LAMPS INOPERATIVE
A1 CHECK THE VOLTAGE AT THE LIGHT SENSOR
  • Ignition OFF.
  • Disconnect: Light Sensor C2360 (EATC).
  • Disconnect: Light Sensor C287 (EMTC).
  • The ignition is on.
  • Turn the headlamp switch to the AUTO LAMPS position.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 Ground

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 Ground

Is the voltage approximately 5 volts?
Yes INSTALL a new light sensor.
No GO to A2
A2 CHECK THE BCM (BODY CONTROL MODULE) OPERATION
  • Disconnect and inspect all BCM connectors.
  • Repair:
    • corrosion (install new connector or terminals - clean module pins)
    • damaged or bent pins - install new terminals/pins
    • backed-out pins - install new pins as necessary
  • Reconnect the BCM connectors. Make sure they are fully seated and locked.
  • Operate the system and determine if the concern is still present.

Is the concern still present?
Yes CHECK OASIS for any applicable technical service bulletins (TSBs). If a TSB exists for this concern, STOP this test and FOLLOW the TSB instructions. If no TSBs apply to this concern, INSTALL a new BCM.
REFER TO: Body Control Module (BCM) (419-10 Multifunction Electronic Modules, Removal and Installation).
No The system is currently operating correctly. The concern may have been caused by module connections. ADDRESS the root cause of any connector or terminal issues.

Exterior lamps always on


For wiring diagrams and connector information, refer to Section 71 of the Wiring Diagrams.

Normal Operation and Fault Symptoms


REFER to: Exterior Lighting - System Operation and Component Description (417-01 Exterior Lighting, Description and Operation).


DTC Fault Trigger Conditions


Trouble Code Description Fault Trigger Conditions
B1A85:21 Ambient Light Sensor: Signal Amplitude < Minimum Continuous DTC that sets when the BCM detects a short to ground in the light sensor input circuit.
B1A85:22 Ambient Light Sensor: Signal Amplitude > Maximum Continuous DTC that sets when the BCM detects an open or a short to voltage in the light sensor input circuit.

Possible Sources

  • Wiring, Terminals or Connectors
  • Light Sensor
  • Headlight Switch
  • BCM

Visual Inspection and Preliminary Diagnosis

  • Inspect the headlamp switch for damage.
  • Inspect the light sensor for damage.

SPECIFIC TEST B: EXTERIOR LAMPS ALWAYS ON
B1 CHECK THE BODY CONTROL MODULE (BCM) DIAGNOSTIC TROUBLE CODES (DTCS)
  • The ignition is on.
  • Using a scan tool, perform the BCM self-test.

Is DTC B1A85:21 or B1A85:22 present?
Yes For DTC B1A85:21 GO to B3
For DTC B1A85:22 GO to B5
No GO to B2
B2 CHECK THE VOLTAGE AT THE LIGHT SENSOR (NO DTCS PRESENT)
  • Ignition OFF.
  • Disconnect: Light Sensor C2360 (EATC).
  • Disconnect: Light Sensor C287 (EMTC).
  • The ignition is on.
  • Turn the headlamp switch to the AUTO LAMPS position.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 Ground

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 Ground

Is the voltage approximately 5 volts?
Yes INSTALL a new light sensor.
No GO to B10
B3 CHECK THE VOLTAGE AT THE LIGHT SENSOR (DTC B1A85:21)
  • Ignition OFF.
  • Disconnect: Light Sensor C2360 (EATC).
  • Disconnect: Light Sensor C287 (EMTC).
  • The ignition is on.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 Ground

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 Ground

Is the voltage approximately 5 volts?
Yes INSTALL a new light sensor.
No GO to B4
B4 CHECK THE LIGHT SENSOR INPUT CIRCUIT FOR A SHORT TO GROUND
  • Ignition OFF.
  • Disconnect: BCM C2280E.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 Ground

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 Ground

Is the resistance greater than 10000 Ohms?
Yes GO to B10
No REPAIR the circuit.
B5 CHECK THE VOLTAGE AT THE LIGHT SENSOR (DTC B1A85:22)
  • Ignition OFF.
  • Disconnect: Light Sensor C2360 (EATC).
  • Disconnect: Light Sensor C287 (EMTC).
  • The ignition is on.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 Ground

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 Ground

Is the voltage approximately 5 volts?
Yes GO to B6
No GO to B8
B6 CHECK THE LIGHT SENSOR
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 C2360-5

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 C287-5

Is the voltage approximately 5 volts?
Yes INSTALL a new light sensor.
No GO to B7
B7 CHECK THE LIGHT SENSOR GROUND CIRCUIT FOR AN OPEN
  • Ignition OFF.
  • Disconnect: BCM C2280E.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-5 C2280E-22

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-5 C2280E-22

Is the resistance less than 3 ohms?
Yes GO to B10
No REPAIR the circuit.
B8 CHECK THE LIGHT SENSOR INPUT CIRCUIT FOR A SHORT TO VOLTAGE
  • Ignition OFF.
  • Disconnect: BCM C2280E.
  • The ignition is on.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 Ground

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 Ground

Is there voltage present?
Yes REPAIR the circuit.
No GO to B9
B9 CHECK THE LIGHT SENSOR INPUT CIRCUIT FOR AN OPEN
  • Ignition OFF.
  • Action:
    Click to display the connectors

    For vehicles with EATC


    Positive lead Measurement/Action Negative lead
    C2360-4 C2280E-10

    Click to display the connectors

    For vehicles equipped with EMTC


    Positive lead Measurement/Action Negative lead
    C287-4 C2280E-10

Is the resistance less than 3 ohms?
Yes GO to B10
No REPAIR the circuit.
B10 CHECK THE BCM (BODY CONTROL MODULE) OPERATION
  • Disconnect and inspect all BCM connectors.
  • Repair:
    • corrosion (install new connector or terminals - clean module pins)
    • damaged or bent pins - install new terminals/pins
    • backed-out pins - install new pins as necessary
  • Reconnect the BCM connectors. Make sure they are fully seated and locked.
  • Operate the system and determine if the concern is still present.

Is the concern still present?
Yes CHECK OASIS for any applicable technical service bulletins (TSBs). If a TSB exists for this concern, STOP this test and FOLLOW the TSB instructions. If no TSBs apply to this concern, INSTALL a new BCM.
REFER TO: Body Control Module (BCM) (419-10 Multifunction Electronic Modules, Removal and Installation).
No The system is currently operating correctly. The concern may have been caused by module connections. ADDRESS the root cause of any connector or terminal issues.

Test yourself

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