My install guide for speedometer correction on a 2004 GX470 (1 Viewer)

[rmswins]

Thanks for stopping by.

What: This is an install guide for most speedometer correction modules (SCM) on a 2004 Lexus GX470. I used the SpeedoHealer v4 Universal Kit but these instructions should apply for most SCMs because they all seem to be fundamentally the same: input speed is read by the SCM, which is then “corrected” and output to the speedometer. Please note that I don’t know what the wire colors are on other GX470 model years but hopefully you learn enough from this guide to pull the right wiring diagrams for your GX and validate wire colors and pin locations for your specific model year. If you follow this guide and find that the wire colors are the same for your different model year GX, please help other members and post your findings in the comments section.

Why: To correct your speedometer to true ground speed after installing different sized tires. I’m also writing this because I couldn’t find a GX470 specific install guide.

Installation Summary: Vehicle speed sensor wire into the speedometer cluster is the pink with light blue stripe wire on connector C11 pin position 15 (C11-15). Cut this wire and connect the wire closest to the harness to the speed input wire of your SCM (for SpeedoHealer this is the white wire). Connect the wire closest to the speedometer connector to the speed output wire of your SCM (green wire on SpeedoHealer). Connect the SCM power wire (red) to a 12V power-on-ignition wire; I used connector C11 pin position 2 (C11-2) which is a black wire with red stripe. Connect the SCM ground wire (black) to a known ground; I used connector C9 pin position 9 (C9-9) which is a brown wire. Program your SCM using the instructions for your kit. Enjoy!

Theory:
1. Speed signal wire: Diagnostic 05-238 shows us that vehicle speed is consolidated at the Skid Control ECU, is sent to the combination/accessory meter (also called an instrument cluster and houses our speedometer), and then travels to the ECM. This means that if we want to correct our speedometer, we should place the SCM in between the Skid Control ECU and the instrument cluster. This also explains why I couldn’t find a “VSS” (Vehicle Speed Sensor) wire in the wiring diagrams. I tried to follow the 4Runner and Prado install guides on other forums but their wire colors didn’t match up to my US spec 2004 GX470. Instead, I found that our Accessory Meter wiring diagram calls out the C11-15 wire as the speed input into the instrument cluster from the Skid Control ECU.

Diagnostic 05-238

Accessory Meter Wiring Diagram for Speed Signal

Pin position 15 on C11 connector

2. Power wire: I wanted a wire that was only powered on ignition because I wasn’t sure if this SCM or any other could cause a parasitic power draw. The Combination Meter wiring diagram shows that C11-2 wire is fed power only on IG2 (AKA last key click position before engaging the starter). I tested this with my multimeter; key out, key in, key to IG2, key to crank.

Combination Meter Wiring Diagram for Power

3. Ground wire: Same process as power, C9-9 goes to ground. Again, I tested this with my multimeter in all key settings.

Combination Meter Wiring Diagram for Ground

I can only insert 5 images per post, so thread will continue below.

 

[rmswins]

Pin position 9 on C9 connector (and note that it is an identical connector layout to C11 and for that matter, C10 and C12)

If you need more help, I’ve broken down the information below:
Tools:
Marker like a sharpie
#2 Philipps Screwdriver
Needle nose pliers
Small flashlight
10mm socket, extension, and ratchet
Multimeter (if you want to test your work)
Nylon pry tool for trim removal
Side Cutter Pliers
20-22AWG Wire Strippers
2x T-Splice for 20-22AWG wires (if you buy the same SCM I did, you won’t need this)
Crimping tool (if you buy the same SCM I did, you won’t need this)
Depending on your favorite way to connect wires, either a soldering iron and heat shrink and solder; or 2x wire splice connectors

Steps:
1. Make this easy on yourself and insert your key into the ignition switch—but don’t turn the key—and once the steering wheel auto-extends out, use the steering wheel adjustment knob to extend the steering wheel as far out (towards you) as possible and then down (to the floor) as far as possible.
2. Remove the instrument cluster by watching the first minute and a half of this video or reading the additional steps below:

a. Using your nylon pry tool: pry the wood trim piece off that sits just below your driver’s side air vent.​

b. Using your nylon pry tool: pry the plastic ring off from the ignition key hole area.​

c. Gently pry towards you on the lower instrument panel near the key hole area until you unclip it. You’re basically trying to give just enough room to remove the instrument cluster bezel so no need to remove the whole panel.​

d. Next follow steps 35 & 36 from the Repair Manual 71-18, but note the following:​

Repair Manual 71-18

i. When I did step 35.(a) the screws did not just fall out. They are plastic screws that are inserted into a pressure clip (see my pictures) They only backed out maybe an eighth of an inch, then I had to gently pry them out with needle nose pliers. The outer ring retainers were still left in there but I gently worked those out by pulling the bottom of the instrument cluster finish panel toward me (which releases it from the dashboard) and then pulling down on the finish panel to release the clips from the top.​

Detail view of "philipps screws" at the top of the instrument cluster bezel

ii. Use a 10mm socket for step 36.(b) Also, do not yank the instrument cluster out as you should feel no resistance once the bolts are completely backed out. If you feel resistance, it means you did not loosen the final two bolts from this step far enough. These bolts have really long threads and do not detach from the instrument cluster. Instead, these bolts are what keep the electric plugs on the back attached to the instrument cluster. What I did was loosen these and occasionally push on them to detach the electrical plugs from the back of the instrument cluster. I kept doing this until the instrument cluster finally released from the dashboard.​

Bolts from step 36.(b) noted with red arrows

3. Slice and dice wires

a. We left the car battery connected up to this point so you can test power and ground. Before we start identifying wires on the car, let’s visually establish the connector labels so you can apply the wiring diagram to what you see in front of you.​

i. We are only going to be working with the connectors that were plugged in behind those two bolts. You’ll notice that each of the two large white connectors are actually housings that hold two additional white connectors. From driver’s side to passenger’s side (US spec models only) the connectors are C9, C10, C11, and C12 respectively. Connectors C9 and C10 are paired on the driver’s side housing. Connectors C11 and C12 are paired on the passenger’s side housing. We’ll only be using C9 and C11. Note that on the wiring diagrams C9 = A; C10 = B; C11 = C; C12 = D. This is important if you want to double check my work since the wiring diagrams call out pin location followed by A-D. For example the Skid Control ECU speed input is simply labeled 15 C in the wiring diagram which corresponds to pin 15 on connector C11 (C11-15).​

Connector labeling

 

[rmswins]

ii. Recall that our 12V power-on-ignition wire is C11-2 and ground wire is C9-9. You’ll get 0V with key out or key in (without turning the key). You’ll get 12V in IG2 and it will remain on 12V if you turn the key further to engage the starter.​

iii. Now that we've tested all wires, we can disconnect the car battery​

b. I’d suggest testing out how you want to route the SCM power and signal cables before you start cutting and connecting. Test out a few locations and start to plan out your wires. I dropped mine directly behind the dash so it would route easily to the fuse access panel. Your two signal wires and power wire from the SCM go to the passenger side connector and your ground wire from the SCM will go to the driver side connector. Note that these connectors sit at the top of the instrument cluster so make sure the SCM wires have enough length to your planned mounting position. You’ll need to access the SCM to program speedometer boost or reduction.​

c. A flashlight helps here: Locate the C11 connector, then identify pin position 15. It should be a pink wire with light blue stripe. Take your time here because I noticed that pin position 14 has a violet wire with dark blue stripe and if you don’t have enough light you could choose the wrong wire. Double check that you have a hold of the pink with light blue stripe wire from pin position 15.​

i. Mark where you want to cut the wire with a marker. Place the connector housing back into the dashboard and note that the connector housing must sit flush with all wires getting routed down the sides and back of the housing, that’s why there are channels back there. With the connector housing still connected to the dashboard check and see if you can see your mark of where you plan to cut. If you can’t, mark closer to the harness side and check again. You don’t want to cut too close to the connector housing and have the splice connector or solder joint squished in the wire channels. Best case you must apply some force to get the instrument cluster back in, worst case you won’t get the instrument cluster to sit right.​

Connector Housing and Wire Channel locations

ii. Pull the connector housing back out and triple check you have the right wire. Cut the wire. Now notice one end of the wire is sticking out from the dashboard side harness and the other end of the wire is dangling from the back of connector C11. Take your SCM and connect—using your favorite method—its speed input wire to the wire sticking out from the dashboard side harness (for the SpeedoHealer it is the white wire). Connect the SCM speed output wire (for the SpeedoHealer it is the green wire) to the wire dangling from connector C11. Check the photo above and note the white wire in the middle is going to the wire harness and the green wire is going into connector C11.​

d. My SpeedoHealer kit came with T-splices. Grab these (they should be red) or whatever splice you’d like.​

i. We’re going to tackle the power (red on SpeedoHealer) wire first because it’s on the same C11 connector that we just performed surgery on. Locate pin position 2 on connector C11. It should be a black wire with red stripe.​

1. Follow step 3.c.i. from above to plan out your splice location. It’s even more critical to plan this splice out because T-splice connectors are larger than in-line splice connectors.​

2. Once you’re confident that the T-splice won’t bind behind the connector housing, splice in your SCM power wire (red on SpeedoHealer)​

ii. Ground wire is on connector C9 so move over to the driver’s side connector housing and use the diagrams from above. Locate pin position 9. Be careful here too because pin position 10 has a brown wire that comes in from the fuel sender.​

4. Clip the connector housings into the holes on the back of the dashboard. If you’ve planned out your splices right the connector housing should click into place. The photo directly above shows how the back of the connector housing fits into the holes in between the wire channels.
5. Install the instrument cluster. Take note that the connector housing bolts need to be tightened until you hear and feel an audible click/pop, so use your 10mm socket and ratchet here. They can’t be overtightened and will click when you finally reach the end of the threads, just like a gas cap. If you don’t tighten these enough you won’t make a solid connection which can cause things like… an instrument cluster that doesn’t light up (don’t ask me how I know).
6. I didn’t install all the other trim pieces until AFTER I tested the SCM
7. Connect the car battery
8. Turn your key to IG2, again the last stop before cranking the engine. Follow the instructions in your SCM kit to set your calibration.
a. My specific calibration for my tires (255/80/R17) using SpeedoHealer was setting a positive 0005.7 which equates to a +5.7% speedometer increase. I found this by driving the car up to 70mph as read on the car’s speedometer and checking what my GPS speedo app was reading out as actual speed. Since GPS speed was 74mph, take (74/70) - 1 = 0.057 or 5.7%
b. Toyota factory manual states +/- 10% speedometer difference is within spec, so I don’t think I’ll have any catastrophic issues by creating a 5.7% speed difference between the skid control ECU and ECM. I’m not guaranteeing anything so do this at your own risk.
9. Once everything checks out, assemble everything and mount the SCM wherever you please

 

[carazytrk]

Thanks for the great write-up. I wish google would have made this easier to find as it would have definitely helped me out. I had to wade through Prado 120 and 4runner posts and Toyota wiring diagrams to find this info.

 

[rmswins]

Thanks for the great write-up. I wish google would have made this easier to find as it would have definitely helped me out. I had to wade through Prado 120 and 4runner posts and Toyota wiring diagrams to find this info.

No problem! I searched quite a bit through Prado and 4Runner forums too and found that they had different wire colors than mine. Had to teach myself a very basic version of reading wiring diagrams to figure it out.

 

[carazytrk]

Here is the picture I created earlier today. I found this article by searching "GX470 C11-15" LOL

 

[carazytrk]

I installed a Dakota Digital SGI-100BT using the wiring suggested in the above post. This SCM has a Bluetooth interface so I could bury it in the dash.

I decided on at 15.5% over correction for my 315/70R17's

App settings are attached.

 

[Rednexus]

Great post! I will likely go this route as it appears inexpensive and relatively easy, without messing with the skid control system.

One question. Will correcting the speedometer also correct the odometer and MPG readings, or just the speedometer itself?

 

[carazytrk]

Great post! I will likely go this route as it appears inexpensive and relatively easy, without messing with the skid control system.

One question. Will correcting the speedometer also correct the odometer and MPG readings, or just the speedometer itself?

It'll fix everything. The speed signal goes through the cluster before going to the ECU and the rest of the computers. This will correct the ODO and MPG readings, it'll also correct the miles to empty estimates.

 

[Rednexus]

It'll fix everything. The speed signal goes through the cluster before going to the ECU and the rest of the computers. This will correct the ODO and MPG readings, it'll also correct the miles to empty estimates.

Thanks! I'll tackle this later this fall. $100 for the Dakota Digital unit is cheaper than the speeding ticket that will eventually come from the 4.5% error in my GX on 32's.

 

[carazytrk]

For the Dakota Digital unit, I used OUT2 instead of OUT1. OUT1 is an AC signal and the cluster is looking for a square wave.

 

[rmswins]

Here is the picture I created earlier today. I found this article by searching "GX470 C11-15" LOL

View attachment 2781412

Yep, thats the same wire. Haven’t mastered the diagrams enough to know how to diagnose problems but I’ll get there someday.

 

[GX470Upgraded]

Was able to have the Dakota Digital installed a few weeks ago thanks to this write up, Thank you very much. Ive driven 300+ miles and verified the MPH thru a GPS, 2 cars set on cruise, 4 speed signs and 1 police officer radar gun(friend). The RPM is also where it should be and i can not calculate my MPG correctly. Again thank you for the info.

 

[mudwagon]

Anyone in a 460 give this a shot yet? Or know of any 460 owners that have? I have no problem tackling that portion myself, but would be easier if it's been documented before. Not sure if 470/460 is similar enough, but give the vast differences I would guess not.

 

[carazytrk]

Anyone in a 460 give this a shot yet? Or know of any 460 owners that have? I have no problem tackling that portion myself, but would be easier if it's been documented before. Not sure if 470/460 is similar enough, but give the vast differences I would guess not.

Why not get something like OVTune and do it electronically? There are no tuning option for the 2003-2004 GX470

 

[mudwagon]

Why not get something like OVTune and do it electronically? There are no tuning option for the 2003-2004 GX470

If you know of a tuning company working on 1UR let me know but there’s not a single aftermarket program with unlock codes for these that I’m aware of. I haven’t tried accessing with OBD CAN tools yet but a buddy works for Toyota, so might have some other tricks I’ll try first. Just looking for an easy solution at this point and snipping 4 wires to go in line is easy enough.

 

[carazytrk]

If you know of a tuning company working on 1UR let me know but there’s not a single aftermarket program with unlock codes for these that I’m aware of. I haven’t tried accessing with OBD CAN tools yet but a buddy works for Toyota, so might have some other tricks I’ll try first. Just looking for an easy solution at this point and snipping 4 wires to go in line is easy enough.

I found a possible lead in the wiring diagrams. Good luck with your research.

EDIT: I found the SP1 input. This is your signal wire.

 

[fourleggedfish]

I installed a Dakota Digital SGI-100BT using the wiring suggested in the above post. This SCM has a Bluetooth interface so I could bury it in the dash.

I decided on at 15.5% over correction for my 315/70R17's

App settings are attached.

The Dakota Digital unit on Amazon says not for use with ABS. Is your ABS still working?

 

[LRDV8R]

The Dakota Digital unit on Amazon says not for use with ABS. Is your ABS still working?

I just installed this unit. Haven't driven the car around yet but I'll confirm if it works once I do

 

[LRDV8R]

No obvious issues with abs. Will need more miles to confirm, but I don't foresee any issues.