Automatic KDJ120 with suspected short between brake and reverse (1 Viewer)

[CoinCoin88]

Hello everyone,

I have stumbled many times across this forum as I'm trying to troubleshoot my Dad's 120 that has been acting up for more than a year now. It doesn't drive a lot and is well taken care of. There's already been a trip to his regular Toyota dealership, they kept it for a week and "didn't find anything wrong" even with thorough explanation of how to reproduce the issue. Though they charged a very thorough diagnostic and "reset some ECUs, that'll make things go away" (no comment...). That episode made me buy an OBDLink dongle.

So. It's an automatically 120 with the common 3L 1KD diesel engine, 130k km, overall in excellent shape. Last year while driving it, I noticed that hitting the brake pedal would faintly light indicators related to being on reverse gear : the little "R" on cluster panel (where all gears have their light indicator (P-R-N-D-L-2), as well as the red diode for "R" on the shifter plate, and finally, it also faintly lights up the actual reverse signal light the rear. All brake lights work normally. The reverse light also works normally when in R position. I tried all likely culprits : trailer socket is clean and un hooking it in the left trim in trunk does clear that behavior; all fuses seem ok ; removed the brake pedal switch and disassembled + tested it with my multimeter, didn't look shorted. At some point (explanation below) it lighted several lights on the dashboard : VSC TRC, VSC OFF, ABS, and the stabilisation control one (pic attached). Power cycling the car makes these disappear. The electric "short" (?) between R and brakes is intermittent : sometimes it'll happen, sometimes not, irrespective of other conditions (blinkers off or on, (head)lights turned off or on...

Fast forward to now, I took the car again a few days ago. Without even turning ignition, same electrical issue between brake and R. No DTC at all. Then I put it in reverse, drove our the parking, and there is the Christmas tree on dashboard again: the systematic way to cause the lights to turn on is to 1) experience that electric short and 2) put on reverse and move a few meters. OBDLink showed (see attached, again) :
- P0705 : transmission range sensor circuit malfunction
- C1223 : ABS control system malfunction
- C1249 : Open circuit in stop light switch circuit

Clearing the DTC's and power cycling the car, they remain gone... Until the next episode of short + put car in reverse. The same code are thrown then.

I started digging again and unplugged the PNP sensor under the car. Car won't start anymore and immediately throws P0705, leading me to believe that sensor is not malfunctioning but is actually impacted by another electric failure, when it arises. A failing ABS module doesn't sound likely, because this wouldn't be intermittent.

A bit clueless now. Obviously bringing it to a skilled dealership would be an option but I don't know any and the previous attempt at our local dealer clearly shows they don't care, or are not experienced, or both. Plus, I'm definitely fond of DIY'ing these things. I'm very inclined to believe there's a short somewhere between brake lights and reverse light, which throws some sensor our of normal operating range under some conditions (say, legit turning on of reverse light + stop lights), cascading to VSC and ABS lights and codes. But I have no idea as to where to look for such a short.

Thanks for any ideas!

 

[2001LC]

I've no experience with the 120. But in the 100 series. When I get strange electrical issues/gremlins. I look for 2 things first:
1) Any aftermarket wiring or components.
2) Any water entry into cabin.

Here I first look if windshield has every been replaced. It's very common installer creates a leak. We'll get strange issues after rian, snow or washing. Issue typically go away, once water drys out of wiring, grounds and or components. Over time the water leak, may cause permanent damage. With permanent damage, the condition usually becomes constant.​

​

Other leaks come from roof rack mounting holes, and or sun roof drains.

Next I'd get into FSM and go through diagnostic tree for: This would be order I'd follow, unless FSM directs otherwise.
1) C1249 :
2) P0705 :
3) C1223 : Likely just getting this DTC, due to other DTC. But don't assume this!

I'd further look for any common point, between electronic of all gremlins.

 

[CoinCoin88]

Thanks for the heads-up. Just a few threads below was a discussion about windshields and how poor replacements can lead to sh*t. It has definitely been replaced in the past (I even remember getting it cracked on the highway myself and having it serviced later on) but I never bothered checking under these strips left and right. Will do momentarily (kid is napping, have an hour for myself).

For the rest, also agree to go on that order. Do you know if FSM are easy to come by? I don't have one yet. Managed to find a workshop manual but it's not in a very convenient place format either.

 

[CoinCoin88]

Just had a look. It sounds like it's not like on the 100s with a rubber strip and rivets underneath: I couldn't find a rubber strip to remove.

After removing the plastic part at the bottom, here's what I see.

Re: water/humidity, no trace around the mounting holes on the roof, nor around the sun roof. I'm also not sure convinced by water-related issues because it happened right outside the box where it had been sleeping for more than a months. Pretty much like last year.

 

[CoinCoin88]

Oops. Attachments missing, here they are.

 

[CoinCoin88]

Oops, thanks to the mod who moved my thread at the right place. Hadn't realized there was a proper 120 section and I thought 100 series would stand for 1xx. My bad.