Electrical Gremlins

This isn't a "help me" thread so much as throwing it out there because I'm stumped.

Backstory: my girlfriend and I spent a week in Joshua Tree rock climbing, and were headed back to CO during one of the first big winter storms this season on NYE. Trip is about a thousand miles or so. Early morning in the drive I noticed the BSM light on the right mirror was flickering on and off, which is odd because I have an aftermarket bumper and have removed the sensors and have the system turned off at the panel switch.

Next, the backup camera comes up on the screen while going 65 down the highway. It flashes on and off a bit, then stays off. Strange, but okay... then the check engine light comes on, disabling TRAC and cruise control. Something to check out, I guess, but the truck was driving fine still.

Finally, the whole climate system froze. The seats were both at setting 1 (low) but stopped getting warm, though the indicator was still lit. The fan turned off, but the panel indicated it was still set to feet, 82 degrees, fan speed 1. Outside temp read "E°F". Huh. Buttons and dials did nothing to change temp or anything.

Pulled over at an overpass and restarted the truck to see if things would reset. CEL stayed on, and the climate system did not come back at all, the panel was dark and would not turn on.

We continued 50 miles or so, but without climate control and outside temps well below freezing, it was a bit uncomfortable. We stopped at a scenic vista and I found this thread and sure enough the fuse was blown. I replaced it and we got climate back. I grabbed the OBD reader and pulled the code, and it was a "Transmission Position Sensor", I didn't grab a photo but I believe it was P0705. Since the truck drove fine we continued on to home uneventfully, except lots of snow and traffic.

I started the truck this morning, no CEL, no codes, climate control works as expected.

What gives? Could a faulty transmission position sensor cause the BSM light to flicker and trip the climate control fuse? It can certainly make the backup camera engage, but... these other things seem unrelated at the outset.

Anyway, not going to worry too much, but throwing this up for posterity in case it happens again or anyone else has noticed similar occurrences.


E°F


Climate console in its frozen state. After restarting the truck the panel went dark.

 

Nothing is more frustrating that electrical issues in a vehicle. Almost makes you want to sell the dam thing. Wait Toyota run perfect and forever.

I have a strange one. It is hit and miss. It has to do with the factory remote starter on my 2020 taco. It will start, but sometime when I open the door it does not turn off the truck and continues to run. It should stop once the door. I believe that is a stupid design feature, but it is what it should do. If the truck does not stop, I have to push the start button to turn the truck off, or put the truck into gear and the truck will stop as well. The truly frustrating thing is, I can't restart the truck for approximately 15 minutes. You have a remote starter to either warm up your vehicle or cool down your vehicle based on your location and weather. Now after 15 minutes you go back and are either in a hot or cool vehicle. Stupid electrical gremlins.

 

You have a serious short somewhere. Now the fun part: finding it!

Also, check your battery. Low batteries will do all kinds of crazy stuff.

 

Did you do any water crossings?

 

intermittent BSM indicator and backup camera could be a clue to a short or contact between circuits and voltage or ground, like a chaffed through wire insulation. Having both of them happen around the same time could be a clue to where the problem is if you can get access to wiring schematic and find where those circuits are in the same harness, maybe also including the transmission position indicator. The blown fuse points to a short to ground or at least to a circuit that pulled more amps than the fuse could handle. If there have been any modifications to any electrical, that would be a good place to start.

 

"...I have an aftermarket bumper and have removed the sensors..."

This stands out to me. ^^^

My personal rule on a service call is "always start first where the last guy worked", every time I broke that rule I shafted myself...

Inspect every bit of wiring near that bumper install, also check/clean the battery terminals, I have read a few posts where a bad battery connection caused odd happenings.

Please post back any findings and good luck.

 

Check where the main engine wiring harness comes out of the firewall into the engine bay. It's on the driver's side, a large bunch of wires heading into a rubber boot. Had mine chewed up by what I can only assume was a rodent, it was near the firewall so maybe something was trying to chew it's way in? Could explain random and/or intermittent electrical issues.

 

Absolutely, though not super recently. I did hit a flooded road in J-Tree pretty hard and it splashed up over the hood, but probably only 6" of standing water. Good thought.

This is what I was afraid to hear Makes sense, thanks!

Really good thought here, too! This would explain everything happening together pretty well.

Interesting. I installed the bumper in May and haven't seen any issues since, but this is a good thought. I did not tape or otherwise seal the sensor harness, so they're zip tied up under the bumper dangling somewhere, and probably got filled with snow/slush, which could be a clue. I'll investigate and report back. It's been single digits since we returned, so I'm not super keen on getting under the truck again until it's above freezing. I'm kind of a weenie like that.

Ugh, if it's rodents I swear... My buddy did his knock sensor harness because of this, and that is a huge PITA. Can only imagine if it's a larger harness.

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To update: I ran some errands today and the truck started up just fine and did not throw a code. Both seat heaters work, as does the climate control system, so we're "back to normal". I pulled the codes, and there was a stored P0705 but it was not throwing the light. I cleared it and drove ~10 miles over two trips, and it did not show up again. At this point I'm going to investigate the main harnesses through the firewall per ORtoCOTaco, as well as the bumper install per RustyGreen. I'll report back if I find anything, or if the issues pop up again.

Thanks everyone!

 

I second the low battery voltage response. I had a problem recently where all of my interior and exterior lights started flashing and I could hear relays clicking each time. It went away and I tested my battery and it read good but needed to be charged. I ended up replacing it anyway as it is five years old and we are heading into the cold months here.

You may have driven long enough to recharge to a level that doesn't cause the issue. Check your battery voltage now as a baseline and then check again if the issue comes back.

 

If the bsm sensor harness plugs are open and exposed, packing them with dielectric grease and then bagging the ends and ziptie tight and out of the way where water can't get to then easily is a good idea.

 

I'm not sure though. I don't see a battery that's low on voltage blowing a fuse, unless those are two separate issues which is likely not the case but not something that can be ruled out either I presume.

 

Yeah I missed that ...

 

Not saying that it is related to the issue at hand but low voltage can indeed blow fuses.

When voltage falls current will rise to do the same work. This is why fuses blow and breakers trip during brownouts.

Using a common 100 watt household light bulb operating at 120 volts, we can illustrate the relationship.

P = wattage (work, illuminating the bulb)
V = voltage
I = amperage

P/V = I
100/120 = .83
100/100 = 1.00
100/90 = 1.11

 

I would double check any electrical work you have done to make sure something hasn’t come loose or got filled with crap and is shorting out. If everything else checks out I would do a thorough inspection for rodent damage especially if it was parked outside overnight, even more so since it’s getting cold at night. Just a piece of advice, I work part time doing maintenance at a company that has 100s of vehicles on the road. We spray every vehicle that comes in the shop with an anti rust product, including the wiring harnesses because the rodents don’t seem to chew through it.

 

Curious, what is the product?

 

New Hampshire oil undercoat, they have a specific rodent repellent now that I haven’t used, but the original undercoat spray seems to do a fantastic job at keeping the critters out. Haven’t run into any issues with it causing any seals to swell either.

 

Thank you, looks like a comprehensive line of products. The rodent repel might be useful for more than just vehicles.

https://nhoilundercoating.com/

 

Your light bulb analogy is incorrect. Current will decrease as voltage drops through a simple load like a light bulb, hence why a bulb gets more dim when voltage drops.

However, you are correct with an electronic device that draws constant power. It could indeed cause current to rise, but in this case only one fuse blew and no others. I cannot say what would or should have blown if low voltage were the case as that would require digging through a lot of drawings and making assumptions that the loads are all properly fixed by calculating 125% of the rated current and rounding up to the nearest fuse size from there.

Regardless, I still don't believe low voltage to be the culprit. Lastly, thanks for that trip down memory lane with ohms law. I used to have a calculator on my phone but it appears to have poofed into nonexistence. I'll have to find another.

 

Agree, the light bulb is just an easy to understand example to illustrate the math.

I also doubt that a low voltage situation would have blown a fuse on this truck.
This is the calculator I have always used, I'm not too swift with the phone...