Disable/Enable DRL

FlyingLow said:

Hey, did you ever get this fixed? I think I'm having the same issue. My DRL is not working and this happened after replacing my front signal and the HID to LED. Let me know if you were able to fix it. I unplugged the headlight wiring harness a couple of times and still nothing.

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Firstly, I need you to answer a few questions.

• Can you confirm that your DRLs were working fine before the light bulb replacement, or if they work fine when the changes are reverted?
• Is your car US spec or Canadian spec?
• If US spec, does the DRL setting in your gauge cluster screen settings menu change anything? If so, what and how does it change?
• Turn your lighting switch to the second position from the left, do your DRLs light up?
• Park in front of a mirror or window so you can watch the DRLs, with the light switch in the off position, start the car, what's the behaviour of the DRLs, do they light up at any point?
• With your headlight main beams on, are your DRLs on?

I don't have a "fix" yet per se; I didn't like the idea of a non user switchable light so I didn't try to fix it. Currently my DRLs are in a stable condition, albeit probably not in line with normal manufacturer specifications.

To elaborate, I did not probe into the electronics due to the lack of necessary knowledge and laziness, however I've come to a tentative conclusion, which is just a fancy way of saying speculation. I believe the DRLs are controlled by chipsets onboard the headlight assemblies, not anything from the car like BCM. BCM only instructs the headlights to do certain things, but whether or not to execute those tasks or what failure mode to go into, is completely up to the onboard controllers within the headlight assemblies. A reason for this speculation is that the fact the duty cycle, aka brightness, of the DRL is directly controlled within the headlight assembly. The BCM only tells the headlight to turn on DRL high, low, or off. The brightness is set by following a likely factory calibrated preset duty cycle. Some background info: LED brightness is not adjusted continuously like filament lights, but through rapidly turning on and off to give off the perceived brightness to the human eye. This is why they appear to flicker under certain digital camera settings. With the right equipment, you can measure the duty cycle, or pulses of the LED, i.e. how long it's on and how long it's off. Without getting into too much detail about LED manufacturing and how phosphorus works and all that, due to inconsistencies in the manufacturing of LEDs, they're always made to certain tolerances, meaning one batch of LED could have a different brightness than another batch when fully on. To match the brightness of multiple batches, one way to do that without implementing unfeasible tolerances, is through PWM, pulse width modulation, or "rapidly turning on and off" in layman's terms. The brighter one will be set with a lower duty cycle than a brighter one, so that both appear to have the same brightness.

I've probed my DRLs and found their duty cycles, and the two are very different. Makes sense considering mine were replaced at different times and the two were manufactured months apart. The car has no way of knowing how bright the DRLs actually appear, so the brightness must be preset and controlled by the headlight itself. You might be thinking, if something goes wrong, and the DRLs turn off, it could be the result of a decision by the onboard controller or an instruction from the BCM. Through observation of mine, I'm more leaning toward the former, and here's why.

My DRLs displayed erratic behaviour ever since I replaced all turn signal bulbs with LED ones that claim to have built-in resistors. My guess is that the resistance is just barely enough to pass the malfunction check, so the car doesn't report a faulty turn signal and hyper flash, but probably not enough to meet another satisfactory check somewhere. My guess on that somewhere is the headlight's onboard controller. At first my car reported turn signal faults with hyper flashes, but this came and went sporadically, until at some point after I cleared the error codes, it never came back. The initial confusion period, as I'd like to call it, had erratic behaviour such as DRLs seemingly turning on or off randomly, turn signals hyper flash randomly, and the DRLs were even observed to flash with turn signals on rare occasions. After several weeks or months, the symptoms finally settled, and now the behaviour is stable and consistent.

Currently, my DRL behaviour is as follows. With the lighting switch turned to off, when I turn the car on, the DRLs will come on at normal full brightness, but immediately turn off, this is seen as a flash lasting less than half a second, similar in length to a camera flash. They stay off as long as the light switch is in the off position. If I turn the light switch to positioning light position (the second position), regardless of ambient brightness, the DRLs will turn on to the low brightness setting, along with tail lights on at full brightness (the tail lights do not use PWM, they're either fully on or fully off). They stay lit in this dim setting and are stable. However, the strange thing is, if I turn the switch to off, now the DRLs are off, but if I turn on turn signals, either side or all way, after flashing for a period of time (15+ flashes minimum, from rough memory), the DRL on that side will come back on at full brightness, however only for a while. Even with no action, that DRL will eventually turn off by itself after a period of time, maybe a few minutes (again, an estimate from rough memory). I have not tested this with the DRL's on the dim setting, as I cannot remember if the DRLs are on at full brightness when you turn the switch to the second position in bright environments.

My tentative conclusion is that the onboard controller requires a certain electrical load to operate normally, and that requirement is higher than the BCM's requirement for a fault, so if your resistance dips below the onboard controller's requirement, but not below the BCM's requirement, the BCM will not report a fault, but the onboard controller will fall into a failure mode of its own, which is disabling DRL full brightness in my case. The flash can be explained by the onboard controller going into normal procedure and turning on DRLs at full brightness at first when it receives power, but immediately fails an operation check or reads a stored fault condition, and goes into this failure mode turning off the full brightness DRL. If my speculation is correct, there would be no way to "fix" this problem without restoring the electrical load to meet the onboard controller's requirement, unless you "hack" the onboard controller and edit its requirement, which is IMO overly complicated and potentially dangerous, as the failure mode may be there for real protection, as opposed to meeting certain legal or policy requirements. If you would like to restore normal DRL operations, I would advise just adding inline resistors to your lighting modules to match the factory power draw; this would be your easiest and likely safest solution, provided that you use quality parts.

Lastly, if you're able, have a dealership tech or anyone with one of Ford's proprietary scan tools check it out, to see if anything abnormal shows up, just in case there's something I missed. I haven't done that as I don't have connections to utilize a proprietary scan tool, so I can't tell you much about that yet. Again I want to remind anyone who's reading, what I said is still just my hypothesis, as I have no concrete proof yet to back up any of the speculations, other than the observations. Please feel free to voice different thoughts.

It's a long read, but let me know if there's anything else you want to know, and I would appreciate it if you could post updates once you have any. Your information could help me as well.