Ford Mustang (1999-2004) Service Manual: Daytime Running Lamps (DRL) (Diagnosis and Testing)

Refer to Wiring Diagrams Cell 97 , Daytime Running Lamps for schematic and connector information.

Special Tool(s)

73III Automotive Meter or equivalent 105-R0057

Principles of Operation

Daytime Running Lamps (DRL)

The daytime running lamps (DRL) system operates the low beam headlamps at a reduced intensity.

The DRL module (15A270) supplies pulse width modulated (PWM) voltage, approximately 75%-92% of battery voltage, to the low beam headlamps when the following conditions are met:

The parking brake control is released.
The high beam headlamps are disabled.
The ignition switch (11572) is in the RUN position.

The DRL module remains enabled when the low beam headlamps are turned on.

Inspection and Verification

1. Verify the customer concern by operating the system.

2. Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart

Mechanical	Electrical
Damaged DRL module Damaged parking brake signal switch and bracket (15A851)	Blown battery junction box (BJB) Maxi- Fuse FOG+DRL (20A) Damaged wiring harness Loose or corroded connection Damaged DRL module Damaged parking brake signal switch and bracket

3. Verify the headlamps are operating correctly. Correct any concerns before proceeding to the next step. For additional information, refer to Section.

4. Verify the parking brake control is fully released.

5. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.

6. If the concern is not visually evident, verify the symptom and refer to the Symptom Chart.

Symptom Chart

Condition	Possible Sources	Action
The daytime running lamps are inoperative	BJB Maxi-Fuse FOG+DRL (20A). Circuitry. Parking brake signal switch and bracket. DRL module.	GO to Pinpoint Test A .
The daytime running lamps are on with the parking brake set	Circuitry. Parking brake signal switch and bracket. DRL module	GO to Pinpoint Test B .
The daytime running lamps are on with the ignition switch off	Circuitry. Ignition switch. DRL module.	GO to Pinpoint Test C .
The low beam headlamps are on at full intensity in DRL mode	Circuitry. Headlamp switch. DRL module.	GO to Pinpoint Test D .
The low beam headlamps are on at reduced intensity with the headlamp switch on	Circuitry. Headlamp switch.	REFER to Section

Pinpoint Tests

PINPOINT TEST A: THE DAYTIME RUNNING LAMPS ARE INOPERATIVE

Test Step

Result / Action to Take

A1 CHECK THE PARKING BRAKE SWITCH SIGNAL CIRCUIT TO THE DRL MODULE FOR SHORT TO GROUND

Yes

GO to A3 .

GO to A2 .

NOTE: Verify the parking brake control is fully released for this step.

Key in OFF position.
Disconnect: DRL Module C1030.
Measure the resistance between DRL module C1030 Pin 6, Circuit 22 (LB/BK), harness side and ground.

Is the resistance greater than 10,000 ohms?

A2 CHECK THE PARKING BRAKE SWITCH

Yes

INSTALL a new parking brake signal switch and bracket.

TEST the system for normal operation.

REPAIR the circuit. TEST the system for normal operation

Disconnect: Parking Brake Switch C306.
Measure the resistance between DRL module C1030 Pin 6, Circuit 22 (LB/BK), harness side and ground

Is the resistance greater than 10,000 ohms?

A3 CHECK VOLTAGE TO THE DRL MODULE

Yes

GO to A4 .

REPAIR the circuit. TEST the system for normal operation.

Measure the voltage between DRL module C1030 Pin 2, Circuit 477 (LB/BK), harness side and ground.

Is the voltage greater than 10 volts?

A4 CHECK IGNITION SENSE INPUT

Yes

GO to A5 .

REPAIR the circuit. TEST the system for normal operation.

Key in ON position.
Measure the voltage between DRL module C1030 Pin 3, Circuit 298 (VT/OG), harness side and ground.

Is the voltage greater than 10 volts?

A5 CHECK THE DRL MODULE GROUND - CIRCUIT 1205 (BK)

Yes

GO to A6 .

REPAIR the circuit. TEST the system for normal operation

Measure the resistance between DRL module C1030 Pin 4, Circuit 1205 (BK), harness side and ground.

Is the resistance less than 5 ohms?

A6 CHECK THE HIGH BEAM DISABLE INPUT CIRCUIT FOR SHORT TO BATTERY - CIRCUIT 12 (LG/BK)

Yes

REPAIR the circuit. TEST the system for normal operation.

INSTALL a new DRL module.

REFER to Module-Daytime Running Lamps (DRL) . TEST the system for normal operation.

Measure the voltage between DRL module C1030 Pin 5, Circuit 12 (LG/BK), harness side and ground.

Is voltage indicated?

PINPOINT TEST B: THE DAYTIME RUNNING LAMPS ARE ON WITH THE PARKING BRAKE SET

Test Step	Result / Action to Take
B1 CHECK THE PARKING BRAKE SWITCH	Yes INSTALL a new parking brake signal switch and bracket. TEST the system for normal operation. No GO to B2 .
Key in OFF position. Disconnect: Parking Brake Switch C306. Connect a 10A fused jumper wire between parking brake switch C306, Circuit 22 (LB/BK), harness side and ground. Key in ON position Do the DRL turn off?
B2 CHECK THE PARKING BRAKE SWITCH SIGNAL CIRCUIT	Yes INSTALL a new DRL module. REFER to Module-Daytime Running Lamps (DRL) . TEST the system for normal operation. No REPAIR the circuit. TEST the system for normal operation.
Key in OFF position. Disconnect: DRL Module C1030. Measure the resistance between parking brake switch C306, Circuit 22 (LB/BK), harness side and DRL module C1030 Pin 6, Circuit 22 (LB/BK), harness side Is the resistance less than 5 ohms?

PINPOINT TEST C: THE DAYTIME RUNNING LAMPS ARE ON WITH THE IGNITION SWITCH OFF

Test Step	Result / Action to Take
C1 CHECK THE IGNITION SWITCH INPUT TO THE DRL MODULE FOR VOLTAGE	Yes GO to C2 . No INSTALL a new DRL module. REFER to Module-Daytime Running Lamps (DRL) . TEST the system for normal operation.
Key in OFF position. Disconnect: DRL Module C1030. Measure the voltage between DRL module C1030 Pin 3, Circuit 298 (VT/OG), harness side and ground Is voltage indicated?
C2 CHECK THE IGNITION SWITCH	Yes REPAIR Circuit 298 (VT/OG) for short to battery. TEST the system for normal operation. No INSTALL a new ignition switch. REFER to Section. TEST the system for normal operation.
Check the ignition switch; refer to the Wiring Diagrams Cell 149. Is the ignition switch OK?

PINPOINT TEST D: THE LOW BEAM HEADLAMPS ARE ON AT FULL INTENSITY IN DRL MODE

Test Step

Result / Action to Take

D1 CHECK THE LOW BEAM HEADLAMPS INPUT

Yes

REFER to Section.

INSTALL a new DRL module. REFER to Module- Daytime Running Lamps (DRL) . TEST the system for normal operation.

Disconnect: DRL Module C1030.
Are the low beam headlamps still on at full intensity?

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