GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 Eldorado 🢒 Body and Accessories 🢒 Lighting Systems 🢒 Headlamp Low or High Beams Always On

Step

Action

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics

1

Did you perform the Lighting System Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

Operate both the low and high beam headlamps.

Do the low and high beam headlamps operate properly?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Place the gear selector in the PARK position.
  3. Place the headlamp switch in the OFF position.

Do the low beam headlamps remain illuminated?

Go to Step 5

Go to Step 4

4
  1. Place the headlamp switch in the HEAD position.
  2. Place the headlamp dimmer switch in the LOW BEAM position.

Do the high beam headlamps remain on at a reduced intensity?

Go to Daytime Running Lamps (DRL) Always On

Go to Step 7

5
  1. Install a scan tool.
  2. With a scan tool, observe the Head Lamp Switch parameter in the Instrument Cluster (IPC) Inputs data list.

Does the scan tool indicate that the Head Lamp Switch parameter is OFF?

Go to Step 9

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Disconnect the headlamp switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Head Lamp Switch parameter in the Instrument Cluster (IPC) Inputs data list.

Does the scan tool indicate that the Head Lamp Switch parameter is OFF?

Go to Step 21

Go to Step 18

7

With a scan tool, observe the High Beam Switch parameter.

Does the scan tool indicate that the High Beam Switch parameter is OFF?

Go to Step 12

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the headlamp dimmer switch.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the High Beam Switch parameter.

Does the scan tool indicate that the High Beam Switch parameter is OFF?

Go to Step 26

Go to Step 17

9
  1. Turn OFF the ignition.
  2. Disconnect the HEADLAMP relay.
  3. Turn ON the ignition, with the engine OFF.

Did the low beam headlamps turn OFF?

Go to Step 11

Go to Step 10

10
  1. Turn OFF the ignition.
  2. Disconnect the HIGH/LOW BEAM HEADLAMP relay.
  3. Turn ON the ignition, with the engine OFF.

Did the low beam headlamps turn OFF?

Go to Step 14

Go to Step 19

11
  1. Turn OFF the ignition.
  2. Connect a test lamp between the supply voltage circuit of the HEADLAMP relay coil and the control circuit of the HEADLAMP relay.
  3. Turn ON the ignition, with the engine OFF.

Did the test lamp illuminate?

Go to Step 15

Go to Step 22

12
  1. Turn OFF the ignition.
  2. Disconnect the HIGH/LOW BEAM HEADLAMP relay.
  3. Turn ON the ignition, with the engine OFF.

Did the high beam headlamps turn OFF?

Go to Step 13

Go to Step 20

13
  1. Turn OFF the ignition.
  2. Connect a test lamp between the battery positive voltage circuit of the HIGH/LOW BEAM HEADLAMP relay coil and the control circuit of the HIGH/LOW BEAM HEADLAMP relay.
  3. Turn ON the ignition, with the engine OFF.

Did the test lamp illuminate?

Go to Step 16

Go to Step 23

14

Test for a short to voltage in the supply voltage circuit of the HIGH/LOW BEAM HEADLAMP relay switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 19

15

Test for a short to ground in the headlamp low beam relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 25

16

Test for a short to ground in the HIGH/LOW BEAM HEADLAMP relay control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 25

17

Test for a short to voltage in the headlamp dimmer switch high beam signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 24

18

Test for a short to ground in the headlamps on signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 27

Go to Step 24

19

Repair the short to voltage in the headlamp low beam supply voltage circuit of the underhood fuse block. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

20

Repair the short to voltage in the headlamp high beam supply voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 27

--

21

Replace the headlamp switch. Refer to Headlamp Switch Replacement .

Did you complete the replacement?

Go to Step 27

--

22

Replace the HEADLAMP relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 27

--

23

Replace the HIGH/LOW BEAM HEADLAMP relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 27

--

24

Replace the Instrument Cluster (IPC). Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.

Did you complete the replacement?

Go to Step 27

--

25

Replace the Body Control Module (BCM). Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 27

--

26

Replace the Headlamp Dimmer Switch. Refer to Headlamp Dimmer Switch Replacement - On Vehicle in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 27

--

27

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2