2010 6.2 - Hill Descent Control Fault and No Brake Lights

[lorenzo_spag]

I bought my Raptor about 4 months ago and instantly it had started throwing the famous "Hill Descent Control Fault". I did some digging on the forums and read about issues with water in the third brake light, so I removed mine, cleaned it up, connected everything, and then caulked it back in really well because I was getting tired of the issue, but this did not fix it.
I then noticed that I only got the fault when my lights were set to auto and it was dark out, it had nothing to do with rain. So here is the exact scenario I get the fault and the symptoms:

Lights turned to auto, on, or running lights on (any position except off) AND it is dark out (if I cover the light sensor up on the dash). I immediately lose my cruise control, and then the two side brake lights stay on (as if I'm applying the brakes) and the middle taillight does not light up at all. About 10 minutes later it will then throw the "Hill Descent Control Fault" on the dash with the traction control light. No other warnings and no DTC's found (from forscan diagnostic). If I turn the headlights off, then I instantly gain back my cruise control and brake lights, however the fault does not disappear until the next start up. When the headlights are off, all three brake lights work normally.

My next guess was going to be to replace the brake light switch, however, I don't think that is the solution because the brake lights work fine when the headlights are off. I also have what appears to be an LED high mount brake light, and I am guessing this is not EOM. Could this be causing the whole problem? I figured I'd ask before throwing more money at the truck.

Has anyone else had these exact symptoms? As far as I've looked online I have not found these exact symptoms. Thank you!

 

[FordTechOne]

It sounds like your high mount/3rd brake light is internally shorted. When the parking lamps/headlamps are on, voltage from the running lamps in the high mount brake light can short to the brake light circuit. That backfeeds into the BCM, which then sees that the brake lights have voltage when the shouldn’t. This information doesn’t match the brake pedal position switch, so DTCs are set.

To check the 3rd brake light, measure continuity (resistance) using an ohm meter between pins 3 and 5. If there is continuity between those two pins, the lamp is shorted internally.

 

[lorenzo_spag]

It sounds like your high mount/3rd brake light is internally shorted. When the parking lamps/headlamps are on, voltage from the running lamps in the high mount brake light can short to the brake light circuit. That backfeeds into the BCM, which then sees that the brake lights have voltage when the shouldn’t. This information doesn’t match the brake pedal position switch, so DTCs are set.

To check the 3rd brake light, measure continuity (resistance) using an ohm meter between pins 3 and 5. If there is continuity between those two pins, the lamp is shorted internally.

Thank you for your quick feedback! I will give this a try and see if that works.

 

[lorenzo_spag]

Update: @FordTechOne nailed it, that was the issue. I disconnected the high mount brake light and everything was back to normal, no more HDC fault and the remaining two brake lights now work as they should. I plan to order a new high mount brake light soon if anyone has any suggestions on a good one. Thanks!

 

[carsonsvt723]

Thank you for your quick feedback! I will give this a try and see if that works.

Has a replacement of the high mount third brake tail light solved the light problem and the hill descent control problem?

 

[The Car Stereo Company]

look up.

 

[carsonsvt723]

look up.

Oh ****. That post did not show up when I first looked it up lmao.