Toyota Electronic Speedometer Re-Calibration. Franken Taco

I used Robert Canons write up on the Dakota Digital Universal Signal Interface SGI-5 to correct the speedometer in my 4Runner after the 5.29 gears and 285/75/16 tires were added.

All of the information listed below is correct for a 4Runner but is specifically written for a Toyota Tacoma pickup truck. The only thing that is different on a 4Runner is that the Green wire with the Red Stripe on the Tacoma is a White wire with a Blue Stripe on a 1999 4Runner. All of the splicing is done right at the transfer case sending unit and the Converter box is located inside the vehicle.

The SGI-5 Unit installed in my 4Runner, behind the passenger side kick panel.

The following information was written and created by: Robert Canon or Franken Taco fame.

It is located below and at: http://128.83.80.200/taco/speedo.html

Taco's don't have speedo cables to regear in order to recalibrate the speedometer. The Universal Signal Interface Unit from Dakota Digital is a signal processor which recalibrates the signal going from the speed sensor to the electronic speedometer. I thought it was a little pricey at $80 for the Universal Signal Interface Unit and then the cost of the speed dyno session, but it's worth it to me to know my speedo is spot on. One cool rationalization for spending the money; If I ever change tire sizes or gears again all I have to do is recalibrate the Universal Signal Interface Unit. If I have the presence of mind to write down the calibration settings for each set up I can go back and forth with the flip of a few switches. For someone with street and trail wheels, or summer and winter wheels, this would be just the ticket.

It needs only 4 connections: accessory power (only on when the key is on), a ground, signal in, and signal out. I started by pulling the lower dash apart to gain access to accessory power and a ground point. The Universal Signal Interface Unit was placed in the area behind the change tray panel just below the ash tray.Accessory power is attached to the Universal Signal Interface Unit's 12v+ terminal, the ground wire is attached to the GND terminal, the wire from the sending unit side of the splice near the transfer case goes to the SPD IN terminal and, at least on my truck, the speedometer side of the splice went to the OUT 2 terminal.
The speed sending unit on the 4WDs is on the passenger side of the transfer case. There are three wires (pink, blue and green with red stripe) attached. Cut the green with red stripe speed signal wire (the other two are power and ground) 2 or 3 inches from the sending unit. I used butt splices sealed with silicone to splice in a double wire and routed it up through the shifter boot to the Universal Signal Interface Unit. Next I attached a ground wire to a bolt on the left side of the dash brace exposed when the change tray is removed.
These scans from the 1998 factory manual show the speed sensor location for the manual transmission 2wd (left), and the auto transmission 2wd (right). My interpretation is that the location on the manual is the passenger's side rear while the auto has the speed sensor on the driver's side rear.

Next are the wiring diagrams showing which wire is power, signal and ground. The 4WD diagram is virtually incomprehensible but I spell out the connections for the 4wd in a paragraph above.

Once the connections are made the unit is calibrated by throwing the DIPP switches on the right. The correct calibration settings are found by dividing real speed by displayed speed, or vice versa (the instructions that came with the unit specify. I can remember at the moment...). The resulting number is looked up on a supplied table and the DIPP switch settings are shown for the needed amount of correction.

To determine real speed you can either have a friend drive along side and tell you how fast you are going at a given displayed speed or put the cruise control on 60mph and time yourself between mile markers. I opted to have the truck put on a speed dyno for ease and accuracy. We ran the truck up to 60 real speed, noted the displayed speed, divided one into the other, and went to the table with the resulting number. It fell between two values on the table so I picked the closest one. We ran it back up to speed but the displayed speed was still a bit off from actual dyno speed. I tried the setting just above the initial one and we ran it back up to speed. This time displayed and actual speed were spot on.

It's been working like a champ for 9 months or so that I've had it. It's solid state and snuggled in the warm, protective confines of the dash so I assume it will hang in there for the duration. See above for calibration procedures..

UPDATE: After installation of the Atlas II transfer case with it's American sending unit (Chrysler/MOPAR p/n 1-05252438 with a 7/8" nut and square drive key) and going up to 35 inch tires some calibration was in order. The new sending unit has two wires (signal and ground) while the Toy unit had 3( signal, ground, and power). Output 2 placed the signal beyond the ability of the dipp switches to correct so I moved to output 4.