ECU-IG #2 Fuse Blowing

[OBCruiser]

Always a reader and never a poster, until now...

My 2016 LC is intermittently blowing the ECU-IG #2 fuse. When this happens it also:
- Throws code P0705 (Transmission Range Sensor failure)
- Puts the transmission in limp mode
- Fails to display one the dash what gear the vehicle is in
- The pre-collision system shuts down
- Lane departure system shuts down
- Headlight system malfunction (lights still work, but auto-high beams don't

Swap the fuse and it will last a day one time and the next it will blow again before I get out of my neighborhood.

I've done some visual inspections of the wires I can get to, for example the transmission range sensor wiring. Nothing obvious...

Any suggestions, other than taking it to the dealer?

Thanks in advance!

 

[Sandroad]

For something like that, the first things I would check are rodent damage in wiring (either under the hood or under the dash), or water damage to wiring via a corroded connector in the door sills. Something is causing a short in that circuit. Rodents or water intrusion are good places to start. Assuming of course there are no wiring modifications.

 

[GrouchyTech]

It lasts a day because this is a 2-trip detection DTC.

Check for wiring damage. Would be really helpful if you have a techstream and can view the data list.

 

[OBCruiser]

Thank you both. I was thinking wiring damage too. It's been garaged all it's life, so I don't think it is rodents. I also haven't found any other rodent evidence. I was thinking maybe a rubbing wire or vibration could have caused the damage.

Very little aftermarket wiring. I have a trailer brake controller that I removed when this stated, and I have the hamilton carplay unit. Neither one of those is on the fuse that is blowing.

I'll keep looking for wiring damage for now.

 

[GrouchyTech]

Thank you both. I was thinking wiring damage too. It's been garaged all it's life, so I don't think it is rodents. I also haven't found any other rodent evidence. I was thinking maybe a rubbing wire or vibration could have caused the damage.

Very little aftermarket wiring. I have a trailer brake controller that I removed when this stated, and I have the hamilton carplay unit. Neither one of those is on the fuse that is blowing.

I'll keep looking for wiring damage for now.

I get a few garaged rodent damage vehicles each month. Especially when pet food is kept in the garage…

Do a good visual check first.

If you have a multimeter you can get under the truck and check resistance of the range sensor to see if it’s all good. (I have a table with the pins to check and the resistance values)

 

[OBCruiser]

Went over the wiring as carefully as I could in the engine compartment and under the body, and am seeing no signs of rodents or other damage. I am leaning toward testing or just changing the neutral safety switch. I'll probably pull it off after work one night this week. From what I can find online, the test looks easy enough - test for 12 volts on the input plug, then check resistance from the input pin to the other pins with the switch in different gear positions...

 

[GrouchyTech]

Easy way: Clear your codes, monitor for pending DTCs and move the gear selector from park to reverse to neutral to drive, pausing about 5 seconds on each. Check for new pending codes to appear.

 

[OBCruiser]

Thanks. I tried that, and in general trying to clear the codes and monitor for what triggered pending codes. I did the gear shifting as you described while refreshing my scanner and checking codes. What I observed is that I don't get any new codes until the fuse blows. Once the fuse blows, I get the P0705 code. So now I'm thinking it's not the neutral safety switch. Back to wiring or other components, or maybe to the dealer...

I really do appreciate all the help. Thank you!

 

[GrouchyTech]

You either have a short in the range sensor circuit, a bad range sensor (the park/neutral switch), or a bad TCM.

It could be water intrusion at a connector, but since it is passing enough current to pop that 10A fuse that’s not my first thought.

Locate the park/neutral harness starting at the transmission on the passenger side. Wipe the dirt off the plug at the park/neutral switch the harness and unplug it. Inspect the contacts on both ends. It should be clean inside with no corrosion. Very carefully inspect the harness all the way up to where it merges with the engine harness behind the intake at the firewall. Then follow that big bundle all the way to where it plugs into the ECM, which is behind the passenger side firewall. You’re looking for signs of rodent chewing or other damage.

If all that checks out, I would go ahead and replace that park/neutral switch. It’s easy to do yourself, but there is a trick to getting it out.

 

[Alpentalic]

I am grappling with the exact same issue with the exact same presentation also on a 2016… I replace the neutral position sensor thinking it was related but the issue returned. It appears that fault code was just from the cascade that came after the fuse blew- ie the ECU wasn’t reviewing the position data so it threw that code.

I’ve had a Toyota tech run through this and he’s at a loss as well. So many accessories/systems apparently run through that circuit. So his advice was to carry fuses and drive it until it happens and then take detailed notes on what was being used when it blow… not very helpful!

I’ve also found no indication of water or wiring damage, ground faults, etc. after extensive searches.

 

[GrouchyTech]

I am grappling with the exact same issue with the exact same presentation also on a 2016… I replace the neutral position sensor thinking it was related but the issue returned. It appears that fault code was just from the cascade that came after the fuse blew- ie the ECU wasn’t reviewing the position data so it threw that code.

I’ve had a Toyota tech run through this and he’s at a loss as well. So many accessories/systems apparently run through that circuit. So his advice was to carry fuses and drive it until it happens and then take detailed notes on what was being used when it blow… not very helpful!

I’ve also found no indication of water or wiring damage, ground faults, etc. after extensive searches.

Plug a 12V sealed beam headlight into that fuse position. Then, when the condition that caused the fuse to “blow” arises, the light will light and you won’t need a pile of fuses.

 

[Alpentalic]

Ooohh- that’s a good idea- I like it. Thanks!

 

[OBCruiser]

I ran into a wall and ended ip taking it to a shop of a couple guys that used ti work for Toyota. They took a week of going over the car with fine tooth comb, and finally found that the parking brake teeth had nicked a wire, Easy fix once they found it, but it was very hard to find. They also zip-tied the wire to move it away from the parking brake. It’s been good ever since.

It’s not a guarantee, but I hope this is your issue. Good luck!

 

[Alpentalic]

I ran into a wall and ended ip taking it to a shop of a couple guys that used ti work for Toyota. They took a week of going over the car with fine tooth comb, and finally found that the parking brake teeth had nicked a wire, Easy fix once they found it, but it was very hard to find. They also zip-tied the wire to move it away from the parking brake. It’s been good ever since.

It’s not a guarantee, but I hope this is your issue. Good luck!

Oh wow- that’s next level detective work! Was the damage to a wire at the parking brake area in the center console or down under the truck? Thank you!!

 

[bloc]

Oh wow- that’s next level detective work! Was the damage to a wire at the parking brake area in the center console or down under the truck? Thank you!!

No first hand knowledge here but there aren’t any wires that could do this under the rig. Most likely under the cup holder in the center console.

Give it a firm pull upwards and it should pop right out for inspection.

 

[Alpentalic]

No signs of wire/parking brake interactions but I’m leaning toward a liquid-related short in that same area being the cause of my issues.

We had a coffee spill two days before the original issue. I’m wondering if that eventually made its way into a connector and is causing an intermittent short. There’s definitely residue down there. I cycled every other system I can think of that runs through that area including HVAC/recirc servos/all switches and buttons etc. I can’t duplicate the issue and got 30 miles on the truck before it randomly came back.

There doesn’t seem to be any rhyme or reason to what causes it which has me thinking moisture…?

 

[bloc]

No signs of wire/parking brake interactions but I’m leaning toward a liquid-related short in that same area being the cause of my issues.

We had a coffee spill two days before the original issue. I’m wondering if that eventually made its way into a connector and is causing an intermittent short. There’s definitely residue down there. I cycled every other system I can think of that runs through that area including HVAC/recirc servos/all switches and buttons etc. I can’t duplicate the issue and got 30 miles on the truck before it randomly came back.

There doesn’t seem to be any rhyme or reason to what causes it which has me thinking moisture…?

View attachment 4158246

The ratchet portion of the hand brake is toward the bottom of your photo, left of the vehicle. All clear there?

 

[Alpentalic]

The ratchet portion of the hand brake is toward the bottom of your photo, left of the vehicle. All clear there?

Yeah- everything looked intact down under that ratcheting area, well secured with no loose wires interacting with any moving handbrake elements as I cycled it.

 

[bloc]

@OBCruiser was yours popping a fuse associated with hand brake use? Or the damage was done and it would pop at random?