GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 CTS 🢒 Body Systems 🢒 Lighting 🢒 Stop Lamps Inoperative

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Listen for an audible click when the relay operates.

    2.

  2. This step tests for voltage at the coil side of the relay.

    3.

  3. This step verifies that the control module is providing ground to the relay.

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics

Connector End View Reference: Master Electrical Component List

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Observe the stop lamps.
  2. Press and release the brake pedal.

Do the stop lamps operate properly?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

Press and release the brake pedal.

Does the bass relay turn ON and OFF?

Go to Step 6

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the bass relay. Refer to Relay Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil side supply voltage circuit of the bass relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 14

5

  1. Turn OFF the ignition.
  2. Connect a test lamp between the coil side supply voltage circuit of the bass relay and the control circuit of the bass relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Press and release the brake pedal.

Does the test lamp turn ON and OFF?

Go to Step 12

Go to Step 9

6

Probe the switch side supply voltage circuit of the bass relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 7

Go to Step 15

7

Connect a 10-amp fused jumper between the switch side supply voltage circuit of the bass relay and the stop lamp switch signal circuit of the bass relay.

Do the stop lamps illuminate?

Go to Step 12

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the inoperable stop lamp bulb.
  3. Connect a test lamp between the stop lamp switch signal circuit of the inoperable stop lamp bulb and the ground circuit of the inoperable stop lamp bulb.
  4. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

Go to Step 11

Go to Step 10

9

Test the control circuit of the bass relay for an open or a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 20

Go to Step 13

10

Test the stop lamp switch signal circuit for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 20

Go to Step 16

11

Inspect for poor connections at the inoperable stop lamp bulb. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 20

Go to Step 18

12

Inspect for poor connections at the bass relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 20

Go to Step 17

13

Inspect for poor connections at the harness connector of the electronic brake control module (EBCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 20

Go to Step 19

14

Repair the open circuit in the coil side supply voltage circuit of the bass relay. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

Go to Step 20

--

15

Repair the open circuit in the switch side supply voltage circuit of the bass relay. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

Go to Step 20

--

16

Repair the open circuit in the ground circuit of the inoperable stop lamp. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

Go to Step 20

--

17

Replace the bass relay. Refer to Relay Replacement .

Did you complete the replacement?

Go to Step 20

--

18

Replace the inoperable stop lamp bulb. Refer to Tail Lamp Replacement and High Mount Stop Lamp Replacement .

Did you complete the replacement?

Go to Step 20

--

19
  1. Replace the EBCM. Refer to Control Module References for replacement, setup, and programming.
  2. Perform the brake pedal position sensor recalibration procedure. Refer to Brake Pedal Position Sensor Calibration .

Did you complete the replacement?

Go to Step 20

--

20

Operate the system in order to verify the repair.

Did you correct the condition?

System OK

Go to Step 2