Ford Fiesta Quiz
Lighting

Fog 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
~12min read

DTC Chart: BCM

DTC Chart


Trouble Code Description Action
B1046:23 Front Fog Lamp Control Switch: Signal Low GO to Pinpoint Test C
B1A78:12 Front Fog Lamp: Short to Battery GO to Pinpoint Test A
B1A78:14 Front Fog Lamp: Short to Ground or Open Circuit
  • If the fog lamps do not operate, GO to diagnostic test A.
  • If the fog lamps are always on, GO to symptom test C.
U3000:49 Control Module: Internal Electronic Failure The module has permanently disabled the output due to excessive current draw (for example, a short to ground) exceeding the limits the BCM can withstand. The cause of the excessive current draw MUST be corrected before installing a new BCM. First REFER to all other diagnostic trouble codes (DTCs). After correcting the cause of the concern, INSTALL a new BCM.
REFER to: Body Control Module (BCM) (419-10 Multifunction Electronic Modules, Removal and Installation).
For more information on BCM field effect transistor (FET) protection, see
REFER to: Module-Controlled Functions - System Operation and Component Description (419-10 Multifunction Electronic Modules, Description and Operation).

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: Fog Lamps

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).
Both Front Fog Lamps Inoperative Refer to Pinpoint Test GO to Pinpoint Test A
Individual Front Fog Lamp Inoperative Refer to Pinpoint Test GO to Pinpoint Test B
Front Fog Lamps Always On Refer to Pinpoint Test GO to Pinpoint Test C

Pinpoint Tests

Both Front Fog Lamps Inoperative


For circuit and connector information, refer to Cell 86 in 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
B1A78:12 Front Fog Lamp: Short to Battery Continuous DTC that is set on demand when the BCM detects a short to voltage in the front fog lamp relay control circuit.
B1A78:14 Front Fog Lamp: Short to Ground or Open Circuit Continuous DTC that is set on demand when the BCM detects an open circuit or a short to ground in the front fog lamp relay control circuit.
U3000:49 Control Module: Internal Electronic Failure This DTC is set when the BCM has permanently disabled the output driver. The module has permanently disabled the output due to excessive current draw (for example, a short to ground) exceeding the limits the BCM can withstand. CORRECT the cause of the excessive current draw before installing a new BCM. For more information on BCM field effect transistor (FET) protection,
REFER to: Module-Controlled Functions - System Operation and Component Description (419-10 Multifunction Electronic Modules, Description and Operation).

Possible Sources

  • Fuse(s)
  • Wiring, Terminals or Connectors
  • Headlight Switch
  • Fog Lamp Relay
  • BCM

Visual Inspection and Preliminary Diagnosis

  • Inspect the fog lamp bulbs and make sure they are in good condition.
  • Inspect BJB fuses 19 (20A) and 21 (7.5A).
  • Inspect the headlamp switch for damage.

DIAGNOSTIC TEST A: BOTH FRONT FOG LAMPS INOPERATIVE
A1 CHECK THE BCM (BODY CONTROL MODULE) FOG LAMP SWITCH INPUT
  • The ignition is on.
  • Turn the headlamp switch to the off position.
  • Using the diagnostic scan tool, view the BCM parameter identification (PID) data.
  • Monitor the BCM FOG_F_SW PID.
  • Turn the headlamp switch to the parking lamps position and turn on the fog lamp switch.

Does the BCM FOG_F_SW PID change from Off to On?
Yes GO to A4
No GO to A2
A2 CHECK THE FOG LAMP SWITCH CIRCUIT FOR A SHORT TO VOLTAGE
  • Ignition OFF.
  • Disconnect: Headlamp Switch C205.
  • Disconnect: BCM C2280F.
  • The ignition is on.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    C2280F-14 Ground

Is there voltage present?
Yes REPAIR the circuit.
No GO to A3
A3 CHECK THE FOG LAMP SWITCH CIRCUIT FOR AN OPEN
  • Ignition OFF.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    C2280F-14 C205-5

Is the resistance less than 3 ohms?
Yes PERFORM the headlamp switch component test.
See Wiring Diagrams, Cell 149, for circuit and connector information. If the headlamp switch fails the test, INSTALL a new headlamp switch.
REFER to: Headlamp Switch (417-01 Exterior Lighting, Removal and Installation). If the headlamp switch test passes, GO to A10.
No REPAIR the circuit.
A4 CHECK THE BCM (BODY CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)
  • Using a scan tool, perform the BCM self-test.

Is DTC B1A78:12 or B1A78:14 present?
Yes For DTC B1A78:12, GO to A5.
For DTC B1A78:14, GO to A6.
No GO to A9
A5 CHECK THE FOG LAMP RELAY CONTROL CIRCUIT FOR A SHORT TO VOLTAGE
  • Ignition OFF.
  • Disconnect: Fog Lamp Relay.
  • Disconnect: BCM C2280D.
  • The ignition is on.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    C2280D-14 Ground

Is there voltage present?
Yes REPAIR the circuit. CLEAR the diagnostic trouble codes (DTCs) and REPEAT the self-test (required to enable the lamp output driver).
No GO to A7
A6 CHECK THE FOG LAMP RELAY ENABLE CIRCUIT FOR AN OPEN
  • Ignition OFF.
  • Disconnect: Fog Lamp Relay.
  • Disconnect: BCM C2280D.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    C2280D-14 Fog lamp relay pin 2

Is the resistance less than 3 ohms?
Yes GO to A7
No REPAIR the circuit.
A7 CHECK THE FOG LAMP RELAY
  • Ignition OFF.
  • Connect: BCM C2280D.
  • Install a known good fog lamp relay.
  • The ignition is on.
  • Turn the headlamp switch to the parking lamps position and turn on the fog lamp switch.

Do the fog lamps illuminate?
Yes INSTALL a new fog lamp relay.
No For DTC B1A78:12 GO to A10.
For DTC B1A78:14 GO to A8
A8 CHECK THE VOLTAGE AT THE FOG LAMP RELAY COIL
  • Ignition OFF.
  • Disconnect: Fog Lamp Relay.
  • The ignition is on.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    Fog lamp relay pin 1 Ground

Is the voltage greater than 11 volts?
Yes GO to A10
No CHECK BJB fuse 21 (7.5A) is OK. If OK, REPAIR the circuit. If not OK, REFER to the Wiring Diagrams Manual to determine the possible causes of the short circuit.
A9 CHECK THE VOLTAGE AT THE FOG LAMP RELAY SWITCH
  • Ignition OFF.
  • Disconnect: Fog Lamp Relay.
  • The ignition is on.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    Fog lamp relay pin 5 Ground

Is the voltage greater than 11 volts?
Yes REPAIR the fog lamp relay output circuit for an open.
No CHECK BJB fuse 19 (20A) is OK. If OK, REPAIR the circuit. If not OK, REFER to the Wiring Diagrams Manual to determine the possible causes of the short circuit.
A10 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.

Individual front fog lamp does not work


For circuit and connector information, refer to Cell 86 in 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

  • Lamp
  • Wiring, Terminals or Connectors

Visual Inspection and Preliminary Diagnosis

  • Inspect the fog lamp bulb and make sure it is in good condition.
  • Inspect BJB fuses 35 (10A) and 36 (10A).

DIAGNOSTIC TEST B: INDIVIDUAL FRONT FOG LAMP INOPERATIVE
B1 CHECK THE VOLTAGE AT THE INOPERATIVE FOG LAMP
  • Ignition OFF.
  • Disconnect: Left fog lamp C152 or right fog lamp C162.
  • The ignition is on.
  • Turn the headlamp switch to the parking lamps position and turn on the fog lamp switch.
  • Action:
    Click to display the connectors

    Left fog lamp


    Positive lead Measurement/Action Negative lead
    C152-1 Ground

    Click to display the connectors

    Right fog lamp


    Positive lead Measurement/Action Negative lead
    C162-1 Ground

Is the voltage greater than 11 volts?
Yes GO to B3
No CHECK that BJB fuse 35 (10A) or 36 (10A) is OK. If OK, GO to B2. If not OK, REFER to the Wiring Diagrams Manual to determine the possible causes of the short circuit.
GO to B2
B2 CHECK THE FOG LAMP FUSE VOLTAGE CIRCUIT FOR AN OPEN
  • Action:
    Click to display the connectors

    Left fog lamp


    Positive lead Measurement/Action Negative lead
    BJB fuse 35 (10A) Ground

    Click to display the connectors

    Right fog lamp


    Positive lead Measurement/Action Negative lead
    BJB fuse 36 (10A) Ground

Is the voltage greater than 11 volts?
Yes REPAIR the circuit between the fog lamp fuse and the fog lamp.
No REPAIR the circuit.
B3 CHECK THE FOG LAMP GROUND CIRCUIT FOR AN OPEN
  • Action:
    Click to display the connectors

    Left fog lamp


    Positive lead Measurement/Action Negative lead
    C152-1 C152-2

    Click to display the connectors

    Right fog lamp


    Positive lead Measurement/Action Negative lead
    C162-1 C162-2

Is the voltage greater than 11 volts?
Yes INSTALL a new fog lamp bulb.
REFER to: Front Fog Lamp (417-01 Exterior Lighting, Removal and Installation).
No REPAIR the circuit.

Front Fog Lamps Always On


For circuit and connector information, refer to Cell 86 in 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
B1046:23 Front Fog Lamp Control Switch: Signal Low Continuous on-demand DTC that is set when the BCM detects a fog lamp switch circuit short to ground during BCM self-test.
B1A78:14 Front Fog Lamp: Short to Ground or Open Circuit Continuous DTC that is set on demand when the BCM detects an open circuit or a short to ground in the front fog lamp relay control circuit.
U3000:49 Control Module: Internal Electronic Failure This DTC is set when the BCM has permanently disabled the output driver. The module has permanently disabled the output due to excessive current draw (for example, a short to ground) exceeding the limits the BCM can withstand. CORRECT the cause of the excessive current draw before installing a new BCM. For more information on BCM field effect transistor (FET) protection,
REFER to: Module-Controlled Functions - System Operation and Component Description (419-10 Multifunction Electronic Modules, Description and Operation).

Possible Sources

  • Wiring, Terminals or Connectors
  • Headlight Switch
  • Fog Lamp Relay
  • BCM

Visual Inspection and Preliminary Diagnosis

  • Inspect the headlamp switch for damage.

DIAGNOSTIC TEST C: FRONT FOG LAMPS ALWAYS ON
C1 CHECK THE BCM (BODY CONTROL MODULE) DIAGNOSTIC TROUBLE CODES (DTCS)
  • The ignition is on.
  • Turn the headlamp switch to the off position.
  • Using a scan tool, perform the BCM self-test.

Is DTC B1046:23 or B1A78:14 present?
Yes For DTC B1046:23 GO to C2
For DTC B1A78:14 GO to C3
No GO to C5
C2 CHECK THE FOG LAMP SWITCH CIRCUIT FOR A SHORT TO GROUND
  • Ignition OFF.
  • Disconnect: Headlamp Switch C205.
  • Disconnect: BCM C2280F.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    C2280F-14 Ground

Is the resistance greater than 10000 Ohms?
Yes PERFORM the light switch component test.
Refer to Wiring Diagrams Cell 149 for schematic and connector information.
If the light switch component test fails, INSTALL a new light switch.
REFER to: Headlamp Switch (417-01 Exterior Lighting, Removal and Installation).
If the light switch component test passes, GO to C6.
No REPAIR the circuit.
C3 CHECK THE FOG LAMP RELAY ENABLE CIRCUIT FOR A SHORT TO GROUND
  • Ignition OFF.
  • Disconnect: Fog Lamp Relay.
  • The ignition is on.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    Fog lamp relay pin 1 Fog lamp relay pin 2

Is there voltage present?
Yes GO TO C4
No GO to C6
C4 CHECK THE FOG LAMP RELAY ENABLE CIRCUIT FOR A SHORT TO GROUND
  • Ignition OFF.
  • Disconnect: BCM C2280D.
  • Action:
    Click to display the connectors
    Positive lead Measurement/Action Negative lead
    Fog lamp relay pin 2 Ground

Is the resistance greater than 10000 Ohms?
Yes REPAIR the circuit.
No GO to C6
C5 CHECK THE FOG LAMP VOLTAGE SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE
  • Ignition OFF.
  • Disconnect: Fog Lamp Relay.
  • The ignition is on.

Do the fog lamps remain illuminated?
Yes REPAIR the circuit.
No INSTALL a new fog lamp relay.
C6 CHECK THE BCM (BODY CONTROL MODULE) FOR PROPER 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

A quick Ford Fiesta quiz: every answer comes with an explanation and a link to the manual page.