Troubleshooting Open Ground Warning on P3 with Known Solid Ground Connection

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Question:

I have the Prodigy P3 installed on my 2003 Excursion 6.0L diesel using the 3035-P adapter. Intermittently I get the Open Ground No Brakes warning message. No trailer connected. I checked the batteries negative terminal to chassis in the engine bay with multimeter and get good readings 0-19 ohms. I checked the 3035-P from end to end and get good readings 0 ohms. I cant see the white ground wire after it enters a large loom/bundle up around the steering column, so I am not able to confirm the condition of the ground wire all the way back to the battery or chassis, not sure where it terminates. I dont ever recall seeing the Open Ground warning with the trailer connected. And have always had brake control as far as I can tell. No other warning messages have been witnessed before. Can the Open Ground warning be a symptom of anything else? Does it have anything at all to do with my 7-pin connector or the wires leading back to it? Thanks.

asked by: Curt

0

Expert Reply:

The "Open Ground" warning message for the Prodigy P3 Brake Controller # 90195 does typically indicate a weak ground connection with the brake controller itself, but it sounds like you've pretty much ruled this out as a possibility. Since this particular error should technically only display when a trailer is actually connected, I wonder if there might be some debris/corrosion built up inside or around the brake output pin on the 7-Way connector.

Especially since you're dealing with an older vehicle, it's very possible that debris or corrosion have built up around the pins of the Excursion's 7-Way, preventing a solid connection when hooked up with the trailer (which might just not be presenting itself as an issue yet) and maybe leading to a short when you aren't, which is what is triggering that error message.

I recommend inspecting the 7-Way at the bumper, cleaning everything out as needed with a wire brush. The brake output pin in particular is located at the 5 o'clock position.

If this doesn't help please let me know and we can go from there!

expert reply by: Chris R

0

Curt

3/9/2020

Well, I believe what Ive got is a low voltage issue. After chasing all the grounds as mentioned in my original post, I decided to temporarily put a power switch on the brake controller. I did this because it always seemed like Id get the OPEN GROUND alarm after starting the truck, but itd go away if I unplugged it and plugged it back in after idling for a few moments. Immediately after starting the truck my battery voltage reading on the tuner SCTX4 would read 11.2V +/- 0.3V. After a few moments of idling the voltage gets above 14V. And when I put power back to the brake controller at around 14V I dont ever get the OPEN GROUND alarm. Not until I shut if off and it sets for awhile and I start it up again. Im not 100 sure this is the root cause, but sure seems to be. Horizon Mfg. did state that a low voltage situation MAY cause OPEN GROUND alarm. I put the brake controller back into the previous tow vehicle Escalade to see if it would alarm out, but it never did. So, controller itself is probably okay.

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Chris R.

3/10/2020

That is really interesting. It definitely sounds like you at least figured out what's causing that error message. I wonder if maybe the root issue is a weak battery on the Excursion that's in need of replacement in the near future? Since the controller gets power directly from the battery, it might be strong enough to get the vehicle started but not quite strong enough to provide enough voltage for the controller until the alternator charges it back up for a bit. It might be worth it to have the battery tested at a local shop to be sure.

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Troubleshooting Open Ground Warning on P3 with Known Solid Ground Connection

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