Same thing. The dlrs are on when the key is on engine off. When the transmission is park, the dlrs are on. When the the emergency brake is on the dlrs are on. They're not supposed to be. Not a huge malfunction, I understand, but a malfunction none the less. Unless the manual is wrong and the dlrs come on when you turn the key on.

Additional info. The dlr relay is being fed power when the key is on. I took the cover off and can see the contacts moving when the ignition is on. I can push the contacts open and dlrs go off. If the relay is being commanded on, I suppose there could be a problem with the BCM.
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And looking at the description of how the control sides of the three involved relays work, I think they all run through the BCM. The green and black wire going to the DLR relay is controlled by the BCM and that wire powers on the DLR relay. The same wire powers the control side of the headlamp ground relay. I don't see how it can be powered on unless it is being commanded on by the BCM. The white wire going to the headlight power relay is controlled by the BCM. My thought at this point is either I don't understand how the circuit is supposed to work, i.e., whether the dlrs are supposed to be off when in park with the parking brake set, or the BCM is controlling the circuit to be on whenever the ignition switch is on. I don't think there's a short anywhere unless it is internal in the BCM.

 

Jacked and George, to assist in giving you guys a direction (circuit problem towards BCM or BCM itself OR towards the headlamps) you can run a quick test with the DRL Relay removed.

Basically under normal conditions the transistor in the BCM grounds the coil in DRL Relay when the conditions are met (headlamp switch in auto, ambient light sensor reading daylight, park brake released, ignition ON, trans not in park). Any of those conditions not met the transistor does not normally ground the relay coil circuit.




To check if the transistor is grounding the relay coil when it shouldn't (due to wrong/bad input or problem with BCM itself) set the truck up with park brake set and trans in park. Also, if in garage or not in bright daylight place a flashlight shining on the ambient light sensor in the passenger side speaker cover (this is important, before you move forward with the test note how your headlights react with and without the flashlight for a baseline).

1. Remove DRL sensor.

2. Connect a meter red lead to B+ (you can use the B+ post next to the UBEC)

3. Put a lead with appropriate sized wire terminal into the DRL Relay position for pin #1 in the UBEC. Be careful you don't use something bigger than the relay pin so you don't spread or damage the female terminal in the UBEC. You could also use a T-pin or similar, but don't stuff into the terminal, just touch it.




4. With key ON (may need to be running for an automatic) measuring with meter black lead, you should see no voltage or ghost voltage. This means the transistor in the BCM is not grounding the circuit. That's what you want.




5. While key is still ON (maybe running for auto...obviously you'll need helper for this step) release parking brake and move transmission out of PARK. At that point your meter should show battery voltage. This means the transistor is grounding the circuit as it should.




If during step #4 (when brake is set/trans in park) you see battery voltage, your problem is between the UBEC and the BCM/inputs/BCM itself.

At that point I would either backprobe or use a small wire piercing tool on the GRN/BLK wire at the BCM starting the test over again (leave the DRL Relay out and remember you're connecting meter to B+ and measuring at probe at BCM with negative lead). Also important, I am seeing two different connector pin positions for that wire on two diagrams, so take the necessary steps to in sure you are on the correct wire at the BCM.

If you read voltage when you shouldn't, focus on testing inputs to the BCM (different procedures than what is laid out here). If the inputs all test good, than I would suspect the BCM as the problem.

Conversely, if you read voltage at the BCM only when you should see it, then I would say you have a short to ground after the BCM to the UBEC (or in the UBEC itself).

Finally, if during the initial test you read voltage at the UBEC DRL Relay pin #1 female terminal when the conditions for normal DRL operation is met (as shown in pics), I would be confident the BCM transistor is operating correctly and grounding the DRL Relay coil only when it should. I would focus between the UBEC and the headlamps for the circuit issue.

Hope this helps give you guys a direction.

 

Then look at the parking brake warning switch or the lt blue wire to the BCM.

George

 

Thanks for the info. I'll see what I can do to perform the additional tests.

In looking at the picture if your relays, I note my 4pin relays are oriented differently. The black 5pin relays will only go in one way. Do the 4pin relays being installed in the opposite direction make a difference?

 

His DRL circuit works fine which we proved in my previous dialouge with the OP. Everything switches between DRL and regular headlight function properly. This entire thing boils down to the parking brake does not defeat the DRL function at key on with the parking brake applied. The thread is all yours.


George

 

It was the blue wire that was not connected to the parking brake switch. Thanks George. I'm glad you mentioned the wire was blue or I don't think I would have found it back there.

 

Your welcome, glad your fixed up.

Now, as to what's going on in this thread. As we have said before, there is an unwritten rule here that once someone starts diagnostics on a thread we all stand down and let the person helping the OP do their thing and stay out of it unless asked or we run out of ideas. Extra divergent instructions only serves to confuse the OP and turns the thread into a mess. This thread is a classic example. The OP had veered off course and some additional questions and experiments showed us that the entire DRL relay system and its control signals were working properly. His singular and simple issue was a wire on a brake switch. Jumping into this thread as we are getting to that point with this extensive diatribe on testing this entire relay circuit and the BCM transistor drive circuits was adding more derailed and unhelpful motion to a simple problem.

In addition I can assure you that I personally do not need a lesson on reading an electrical schematic, circuit analysis or relay function or test meter operation. I design and test semiconductor and tube amplifiers and countless other types of electronics, have been fixing vehicles for over 50 years, have an electrical engineering degree and ran a company that designed, manufactured, sold and supported circuits with over 5 million transistors on them. I can handle the low side transistor switching of a relay coil. You have energy and are willing to take the time to spit out detailed instructions with pictures and so on. Good, use all that energy to help people here but if you dont get to the thread first and are not being asked for an assist then lets respect the process and get the OP uncluttered and focused help.


George

 

Tell you what rockp2, since you have so much energy and your trying to make your mark here, I am going to stand down and not take any new threads for a while and let you have as many as you would like. A word of advice however is that it takes a lot more than some knowledge of electronics and the ability to read a schematic to get to a truck that's fixed, especially over the internet a thousand miles away one post at a time working with communication challenges, a wide variety of OP knowledge and testing capability. Confirmation bias clouds a quality diagnostic process and targeted fix as it did here. Then there is the parts cannon, ... We can always use more skilled help here so do your thing. I like your energy, lets see you fix some trucks.


George

 

Not really (with the exception of relays that are marked to have diodes in them). The relays GM used on these trucks always have pins #1 & #2 as the relay coil (control wire) pins. So if you notice on the relay, whichever way you turn the relay #1 and #2 will always end up in the control wire corners.