Upgrading to A-TRAC from no VSC

The ABS system in my non-VSC equipped 07 TRD Sport 4x4 was far from working correctly, so I decided to try replacing it with an A-TRAC unit from an 07 FJ Cruiser. Oh and, because it affects this project, I should note that I've already installed an all-wheel drive transfer case from a 2017 Lexus GX460 (same part as 03-09 V8 T4R) and removed ADD, so I have full-time 4WD.

After looking at wiring diagrams, I think the core of this system (the hydro ABS unit) is nearly the same, regardless of the truck it came from. From the wiring diagrams it appears as though the same unit can support multiple drivetrain configurations (MT/AT, 4WD/2WD, etc.). I'm curious what the logical/internal differences of the ECU might/not be across different trucks/PNs.


Parts List (I will try to update this with actual part numbers):
Yaw rate sensor
Stop lamp control relay

FJC parts:
Main engine room wiring harness
Hydro ABS unit
A-TRAC button

• replaces Taco's DAC button
• plug 'n play with exact same connector

Parts from a Taco w/VSC:
Brake pedal assembly
Brake hard lines
VSC Off button

 

The most involved work here is tracing the wiring diagrams from all three trucks. I should probably put all of this into a spreadsheet to make it easier to follow, but here's what I think is most of the mapping; the abbreviations on the non-bullet-ed lines represent pins on the VSC unit's main harness/ecu. If you study things long enough you'll see that most everything for the VSC unit passes through the EA2 connector (gray 22-pin on the FJC's main harness). I was going to try to build an adapter that plugs into the EA2 connector, but since I can't find part numbers for connectors on the main harnesses, it may not be practical. @DaveInDenver can you get these?

NEO: truck in 4wd indicator
- T4R: VSC pin A10 to 4WD pin A20
- Taco: IA3 connector (pin 15, W-B)
- FJC: EA2 connector (pin 12, P-L)

EXI3: rear-diff locked indicator (n/a)
- T4R: VSC pin A26 to VSC pin A1 (ground)
- Taco: IB1 connector (pin 4, L-Y)
- FJC: LA2 connector (pin 11, L-Y)

EXI4: truck in 4Lo indicator
- T4R: VSC pin A21 to 4WD pin A24
- Taco: IA1 connector (pin 42, Y-B)
- FJC: EA2 connector (pin 2, W-L)

EXI: front/rear locked indicator
- T4R: IC2 connector

- VSC pin A27 to 4WD pin B22 (P1): R-L
- 4WD pin B22 (P1) to XFR pin 9 (CDL): R-L​

- Taco: IA1 connector (pin 41, LG-B)
- FJC: EA2 connector (pin 1, GR)

P: park/reverse indicator
- Taco: IA1 connector (pin 39, G-B)
- FJC: EA2 connector (pin 13, Y-B)

CSW: VSC Off/ALSD switch
- Taco: IA1 connector (pin 18, GR-B)
- FJC: EA2 connector (pin 6, R-L)

SP1: speedometer
- Taco: IA1 connector (pin 36, R-Y)
- FJC: EA2 connector (pin 12, GR-R)

BRL: parking brake dash light
- Taco: IA1 connector (pin 21, B-W)
- FJC: EA2 connector (pin 8, B-L)

WA: ABS dash light
- Taco: IA1 connector (pin 19, O)
- FJC: EA2 connector (pin 18, LG-R)

IND: slip dash light
- Taco: IA3 connector (pin 18, R-W)
- FJC: EA2 connector (pin 19, R)

INFR/VSCW: ALSD/TRAC dash light (2WD)
- Taco: IA3 connector (pin 16, LG-R) route to VSC TRAC signal, because no 2WD/ALSD signal
- FJC: EA2 connector (pin 20, Y-R) use ALSD dash light, because no VSC TRAC dash light

WT: VSC off dash light
- Taco: IA3 connector (pin 17, L-W)
- FJC: EA2 connector (pin 9, L-W)

HDCW: ATRAC/DAC dash light
- Taco: IB1 connector (pin 12, L-B)
- FJC: EA2 connector (pin 17, Y-V)

HDCS: ATRAC/DAC switch
- Taco: IA3 (gray 18-pin) connector (pin 4, P-B)
- FJC: EA2 connector (pin 3, P-G)

CANH: databus
- Taco: IA3 (gray 18-pin) connector (pin 1, B-W)
- FJC: EA2 connector (pin 11, B)

CANL: databus
- Taco: IA3 (gray 18-pin) connector (pin 2, W-L)
- FJC: EA2 connector (pin 22, W)

BZ: VSC warning buzzer
- Taco: IA3 connector (pin 6, GR)
- FJC: Buzzer (pin 1, GR-G)

PKB: parking brake switch
- Taco: DC relay connector (pin 6, G-Y)
- FJC: 1E relay connector (pin 1, W-R)

TS: Data link connector
- Taco: DC relay connector (pin 2, R-B)
- FJC: EA2 connector (pin 4, R-B)

D/G: Data link connector
- Taco: DC relay connector (pin 7, W)
- FJC: EA2 connector (pin 15, R-Y)

WFSE: Data link connector
- Taco: DC relay connector (pin 9, V)
- FJC: EA2 connector (pin 5, R-W)

IG1: ecu ignition
- Taco: DC relay connector (pin 3, LG)
- FJC: Junction A28 (pin 8, B-R)

IG2: ignition
- Taco: 1C relay connector (pin 17, O)
- FJC: A27 Junction connector (pin 11, B-O)

STP: stop lamp control
- Taco: 1C relay connector (pin 15, G-W)
- FJC: A27 Junction connector (pin 15, G-B)

STP2: stop lamp control
- Taco: 1C relay connector (pin 15, L)
- FJC: A27 Junction connector (pin 5, G-Y)

STP0: stop lamp control
- Taco: Engine room relay block (G-B)
- FJC: Engine room relay block (B-L)

+BM: 50A ABS motor
- Taco: Engine room relay block (R)
- FJC: Engine room relay block (L-Y)

+BS: 30A ABS solenoid
- Taco: Engine room relay block (Y)
- FJC: Engine room relay block (Y)

XFR Case Ground
- T4R: XFR pin 10 & 6 to ground
- Taco

- XFR pin 4 to junction block PA 19
- junction block PA 19 to 4WD pin 22
- should be able to reuse at XFR case​

 

I’ll be reading this later, something I considered years ago but recognized it’s more than I wanted to jump into after looking into the amount of parts and their costs. You’d be the first I know of, excited to see this done.

 

Honestly, if my brakes weren't so jacked at the moment I wouldn't have ventured down this path. After trying several things I decided to just go ahead and do this, because the cost of replacing the current setup would've only been a little cheaper. Altogether, I'm in the hole at just over $1k for everything. I did score some sweet deals online, though. I probably could've found a way to use the brake pedal assembly that's in my truck and saved another $300, but I was being lazy and used money instead of might.

 

Why does it matter what transfer case you have?

 

I don't think it actually matters which transfer case you have, the VSC/hydro ABS unit should work in any Prado-based truck. However, what I'm going to document in this thread (mostly wiring harness splicing) will be specific to my configuration. If you read up on the VSC and 4WD systems (wiring diagrams, operating modes, etc.) you'll see that the former is largely dependent on the latter. My truck essentially has 4WD from a V8 T4R and I'm trying to add the VSC from an FJC. If anyone goes about a different mix (e.g. just adding VSC to a non VSC taco), at least some of the wiring harness connectors and/or colors would be slightly different.

For example the VSC ECU has a pin that gets signal when the rear diff is locked (EXI3, above). This pin isn't used on the V8 T4R, because it never came with a rear locker; instead it is just hardwired to ground. Similarly, the FJC transfer case is manually switched and has a sensor to indicate which mode it is in; whereas the V8 T4R transfer case is electronically switched and does not use the same 4WD mode sensor to indicate its current mode.

 

@JimSnell here's some awd tcase action for you

 

Little button action for all the late night lurkers out there.

 

I added a spreadsheet to the second post to try and make it easier to follow.

 

Man I've been looking for something like that for a long time

 

Question: If you had kept the ADD system functional in your truck: In theory, couldn't you have had the option to run RWD by locking the center differential and uncoupling the ADD? Would this theoretically put any excessive wear on the center differential to drive around with it locked for hours on end?

EDIT: I noticed in other threads that you have a Torsen in front now. So I am not sure how well that would go over with an uncoupled ADD. But for a truck with a standard open front differential or selectable locker perhaps it would work just fine.

Also, can I ask where you are accessing detailed wiring diagrams for your truck? I have a lot of wiring research id like to do for my 2015... some of it along the same lines as what you have been up to.

 

This won't work. In the V6 T4Rs that have ADD and AWD, truck has to be in 4WD before you can lock the center differential. There isn't a factory wiring setup that allows this configuration. I have no idea if custom wiring would get it done cleanly. My truck is basically just V8 T4R driveline with torsens front and rear..

 

This makes sense that it wouldnt be an available mode using factory controllers and wiring. I was theoretically proposing it being controlled manually with individual toggles and relays.

Was there ever a 4R from the factory that could do RWD, AWD, and 4X4? I have seen a few posts on this forum suggesting that, but perhaps accidently or mistyped.

 

Yes, maybe I didn’t make that clear. There are two transfer cases is prado-based trucks (with interchangeable inputs for auto vs manual transmission). One is part-time 4WD, the other is full-time 4WD (AWD). The V6 T4R I was trying to describe above has the full-time 4WD transfer case, but retains the ADD and thus 2WD, AWD, and fully locked 4WD.

 

Edit: I will take this conversation to our private messages as to not derail your ATRAC thread.