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Clayso
Clayso, Master Automobile Technician
Category: Cadillac
Satisfied Customers: 880
Experience:  ASE Master Certified Automobile Technician. 30 Years Experience.
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My brake lights won't work. All other rear lights work. I

Customer Question

My brake lights won't work. All other rear lights work. I replaced the bas relay.
JA: Have you checked the brake fluid? How's the level and when was it last changed?
Customer: The mechanic can't figure it out. He said when he make it hot to the relay, they work.
JA: What is the model/year of your Cadillac?
Customer: I'm not sue what that means.
JA: What year is your Cadillac?
Customer: 2006 cts
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I haven't tried yet, but I would like too.
JA: Anything else you think the mechanic should know?
Customer: Do you help do it yourself people?
Submitted: 1 year ago.
Category: Cadillac
Expert:  Clayso replied 1 year ago.

Hi There, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience.

If you mechanic has a scan tool that can see the ABS circuit they should be able to see the brake signal from the brake pedal position switch to the Electronic Brake Control Module (EBCM). Without a scan tool you can backprobe the EBCM connector pin C3 orange wire and with a voltmeter check for 12 volts to appear when the brake pedal is applied. Crazy as this may sound I've jumped the relay and turned the brake lights on, when the resistance in the bulbs is to great for the relay to close on its own. Basically the bulbs were defective. Sylvania bulbs will work fine, the cheap bulbs just don't operate properly. If your mechanic needs connector views and or a circuit diagrams for this system let me know. IF you have a voltmeter I can walk you through this circuit to find the problem.

I hope this information is helpful. If you have any questions let me know. You can reply back to me through this thread at any time.

Kindly rate my assistance in a positive manner so I may have credit for helping you.
Positive ratings are greatly appreciated.
Thanks.

Customer: replied 1 year ago.
Thank you.I don't have a voltmeter. My son is bringing the car to me in an hour or so though.
Expert:  Clayso replied 1 year ago.

That's cool. Let me know if the cruise control works.

Customer: replied 1 year ago.
Thanks. No, cruise control does not work.
Expert:  Clayso replied 1 year ago.

Did the cruise quit at the same time as the brake lights?

Customer: replied 1 year ago.
we believe so.
We just got the car. It was a gift to my son from his grandma. It sat in the garage for a few years
Expert:  Clayso replied 1 year ago.

I understand. A voltmeter is needed to check for power at the Electronic Brake Control Module (EBCM). The link below is a diagram of the connector and the location of the supply voltage to the BAS relay.

EBCM Connector C3 Location

Backprobe at the EBCM connector pin C3, Orange wire with a voltmeter. Check for 12 volts to appear when the brake pedal is applied. The ECBM is by the battery with steel lines connected to it. Use a small pin and slide it into the back of the connector at the orange wire in the C3 terminal. The view of the connector to the ECBM is from the module side, the orange wire will be on the harness side. There should be battery voltage when the brakes are applied.

Let me know how this works out for you.

Thanks

Customer: replied 1 year ago.
Ok, we just bought one
Expert:  Clayso replied 1 year ago.

Cool, check and see if there is power on the orange wire when the brakes are applied.

Customer: replied 1 year ago.
I'm not sure where to locate the ecbm
Expert:  Clayso replied 1 year ago.

Let's get to a connector that's easier to work with and maybe where the problem is to begin with. The links below are the location and description for connector C102

C102 Location

C102 Engine to Body Harness

Check the orange wire on both sides of the connector, there should be battery voltage when the brakes are applied. C102 should be on the passenger side between the engine and the body. If there is power on one side and not the other open the connector and make sure the contacts are clean.

Let me know how this works out.

Thanks

Expert:  Clayso replied 1 year ago.

I'm not sure of the shops ability where you had this vehicle last. I'm a member of an automotive technicians network, if you will let me know your zip code I may be able to locate a reputable shop in your area that is fully capable of diagnosing this type of problems. We can only go so far with a voltmeter until a professional level scan tool is needed. I'm sure there are Diagnostic Trouble Codes (DTC)'s stored in the Body Control Module (BCM) for the brake lights and the cruise control. Let me know your zip and I see what all I can find.

Thanks