Speedometer correction device

[XPLORx4]

I would like to report that I have successfully installed into my '97 Pathfinder a device which corrects for speedometer error caused by running oversize tires. I bought a Dakota Digital SGI-5 Universal Speedometer Signal Interface ($85) and after wiring it up and programming the % correction, my speedometer is now dead-accurate with GPS.

 

Before you begin: note your GPS speed when your speedometer reads 50mph. Calculate your speedometer correction ratio using this formula: GPS speed/50=correction ratio. For oversize tires, the ratio will be between 1.00 and 1.20.

 

To install the SGI-5, you will need to remove your instrument cluster to access the wiring harness and locate 2 wires: +12vDC hot when the key is "On" and the VSS wire.

 

On the back of the instrument cluster, there are several connectors. The connector you care about is the vertical white connector closest to the far left of the cluster. On that connector, locate the white/black wire (+12vDC hot when ignition "on") and the light blue wire (VSS signal wire). *If you have a reference manual that shows the wiring diagrams/colors, consult that manual to verify the correct wire color for the VSS and +12vDC are as stated above. Optionally you may use a voltmeter to check DC volts (for the power wire) and AC volts (for the VSS). The VSS will read a varying voltage depending on your speed.

 

I installed a T-tap connector onto the white/black wire and cut the light blue VSS wire. I then attached a male and female bullet connector to the cut ends of the VSS wire. This makes it very easy to revert back to stock condition if needed.

 

The SGI-5 requires 4 wires: +12vDC, ground, input, and output. Obtain 4 30" lengths of 18-22AWG wire, preferably black, red, and two other colors. I used green and purple since that's what I had handy. Strip 1/4" from one end of each wire and tin them with solder. To the other end of each wire, attach the following:

•Black: a ring terminal at least 1/4" in diameter.

•Red: Spade connector (to fit into the T-tap connector)

•Color 1: female bullet connector

•Color 2: male bullet connector

 

Make sure the bare/soldered ends of all 4 wires are together. These ends will insert into the SGI-5. Twist all 4 wires together so they are easy to manage as a bundle.

 

1) Connect ground wire: Remove the 10mm nut holding the inner dash (behind the center of the instrument cluster) to the metal framing behind the dashboard and place the ring terminal over it to provide a ground connection.

 

2) Connect power wire: Attach the red wire with spade connector to the T-tap on the white/black wire

 

3) Connect signal wires: Attach the other two wires with bullet connectors to the appropriate ends of VSS signal wires. Note the wire color you have attached to the end of the blue wire going INTO the instrument cluster. This wire will be inserted into the "OUT1" terminal on the SGI-5. The wire color attached to the blue wire coming from the harness (which originates at the VSS) will be inserted into the "INPUT" terminal on the SGI-5.

 

4) Locate a suitable place to mount the SGI-5 where it will be accessible in the future, but do not mount it yet. First, fish the twisted wire bundle behind all plastic pieces on the inner dash and down and over to where you will mount the SGI-5. (I chose to attach my SGI-5 to the side of the transmission control module using double-sided tape.)

 

5) Insert the power, ground, and signal wires into the SGI-5 terminals. Turn the ignition switch to "ON" but don't start the engine. Confirm that the green LED on the SGI-5 illuminates. If it does not, check your power and ground connections.

 

6) You are now ready to program the SGI-5. There are 4 DIP switches on the SGI-5. Set them as follows:

SW1-3: OFF

SW4: ON

 

Towards the back of SGI-5 instruction manual, you will see a chart full of numbers. On the far right, look under the "Cal Hi" column and locate the number that is closest to the correction ratio you calculated earlier. (The number closest to my correction ratio was 1.049.) In this row, note the numbers under the "Coarse" and "Fine" columns. These will be the settings you program into the SGI-5. (Mine are coarse:1 and fine:12).

 

7) Program the "Coarse" setting. With ignition switch OFF, press and hold the UP button while turning the ignition switch to ON (but do not start the engine) and release the UP button. The green LED will begin flashing the "Coarse" setting. Watch the flashing pattern and pay attention for when there is a longer pause between flashes. Count the number of flashes between pauses. (It will probably be 16.)

 

Press the "DN" button slowly and repeatedly until the number of flashes between pauses matches your "Coarse" setting (probably going to be 1 or 2). To save the setting, turn off the ignition switch.

 

8) Program the "Fine" setting. With ignition switch OFF, press and hold the DN button while turning the ignition switch to ON (but do not start the engine) and release the DN button. The red LED will begin flashing the "Fine" setting. Watch the flashing pattern and pay attention for when there is a longer pause between flashes. Count the number of flashes between pauses. (It will probably be 16.)

Press the "DN" button slowly and repeatedly until the number of flashes between pauses matches your "Fine" setting. To save the setting, turn off the ignition switch.

9) Partially reinstall the instrument cluster so you can verify that your speedometer works correctly while driving. Take a short drive around the block to verify that your speedometer functions. If it does not, check your wiring connections. Remember, the wire from the VSS goes into the INPUT terminal, and the wire to the instrument cluster goes to the OUT1 terminal.

10) Drive the vehicle at normal roadway speeds. Using a GPS, verify your speedometer reading. If it reads too fast, you will need to enter a lower correction ratio from the chart. If it reads too slow, enter a higher correction ratio. Repeat steps 7 and 8 as appropriate until your speedometer reading is accurate.

11) Fully reinstall the instrument cluster and mount the SGI-5 in the location you predetermined.

Congratulations! Your speedometer will now read accurately.

Edited April 19, 2014 by XPLORx4

[CNAM]

Awesome! Need this!

 

 

 

[linkinpark]

You the man.

[adamzan]

Great to see someone has installed one of these on a pathy. There are a couple other ones around like the yellow box and speedo healer. I am going to install one because I swapped in an xterra trans and couldn't get the speed sensor out of my old tranny lol. Plus I run 33s making it useless anyway. Thanks for the write up!

Edited April 20, 2014 by adamzan