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Electronic Speedo Correction
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Electronic Speedo Correction

Date Created: 09/28/2009
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I have a 2004 Rubicon with an electronic speedometer and a speed sensor and reluctor in the transfer case (no gear). I have changed axle gear ratios to 4.88s and I’m running 35” tires, so my speedo was way off.

I purchased a SuperChip FlashPaq #3875 thinking that it would be able to correct my speedo, but it does not work on my ‘04 TJ speedo. (Check post #11 of this thread for SuperChips customer service response to my issues.
Speedometer correction?)
Like so many others, I have searched for a good solution for the speedo problem. What I came up with is a little different than what others have used that I have read about.

I found a speedometer signal correction device that is marketed primarily for motorcycles. It looked very interesting to me. Some of it’s features are:
1. Very small size.
2. Manufactured using surface mount technology (SMT) which is very resistant to vibration and shock.
3. All the electronics are encased in epoxy (potted) and therefore waterproof.
4. It has two banks of memory so you can program for different size tires or one bank for MPH and the other for KPH.
5. It also has a feature that I, and probably most Jeep guys will have little use for. It is the top speed memory (TSM). I can see where a young guy with a fast motorcycle would like to have this to show all his buddies how fast he had ridden.
6. Reasonably priced

This speedometer correction unit is called “SpeedoHealer” and is manufactured by HealTech Electronics. HealTech Electronics Ltd. - Makers of the SpeedoHealer, GIpro and X-TRE -

Almost all late model motorcycles use a three wire speed sensor to generate a signal for their electronic speedometer. Jeeps with electronic speed sensors use a three wire speed sensor to generate the signal for the electronic speedos. After a couple of emails back and forth with HealTech Electonics and some measurements with a digital VOM it looked like the SpeedoHealer would work on my Jeep so I decided to try it.

I ordered their current unit (SH-V4) and a universal wiring harness (SH-U01) directly from HealTech in Hungary. I received the unit and the harness in a few days and was very pleased with the items. They look and feel very high quality. Here is a pic of the SH-V4 package and its contents:
Wire ties
Wire splices
Velcro patch
Top speed memory wires and switch
Jumper plug to run the speedo without the SH-V4 inline

Pic#1&2 Package and Unit

The second package which is not shown, contained the universal wiring harness. I got a little excited and started installing the wiring before I took pictures of the harness package. Not much to it, four wires about 40 inches long in a plastic sheath with a plug on one end to plug into the SH-V4. The wire colors are red, black, green and white.

I choose to run the wires from the area behind the glove box. I removed the glove box by sliding the retainer strap out of its slot and rotated the glove box down until it came loose. You can see the white plug hanging out of the glove box opening. It's pretty small.

Pic#3 Glove Box

I needed more wire to reach the speed sensor so I spliced on enough wire to give me a total length of 8 feet (it is possible to order a custom harness 8 feet long). I ran the wire harness thru a hole in the firewall right next to the heater. I drilled a 3/8th inch hole and fitted a grommet in it to protect the wiring.

Pic#4 Harness thru the firewall

Underneath the Jeep, I ran the wires along side the existing wiring harness that runs on top of the transmission. After this picture was taken and I got everything connected, I went back and used zip ties to tie the SpeedHealer harness to the existing harness.


Back at the speedometer sensor on the tail shaft of the transfer case, here is what the wires look like.

Pic#6 Wires and plug.

On the speed sensor the wire colors are:
Red = +5volts
Black = ground
Tan = speed signal

The Jeep wiring harness that plugs into the the speed sensor wire colors are:
Purple with white stripe = +5 volt
Black with lt. blu stripe = ground
White with orange stripe = signal

I choose to splice the SpeedoHealer wiring harness to the Jeep harness and not directly to the speed sensor wiring. I figured that if I ever have to replace the sensor, I won’t have to redo the wiring. I took my time and stripped about 1/2" of insulation off of the power and ground wires being careful not to cut the wires. I cut the signal wire in two and stripped the two ends.

Pic#7 Wires stripped.

I staggered the location where I hooked up the power and ground so there is little likelihood of the two splices ever getting together. Also makes for a neater package. I also choose to solder the connections and use shrink wrap to preclude future connection problems.

Pic#8 Solder splice

The wires from the SpeedoHealer are:
Red = Power (+3 to +19 volts)(I didn't have red so I used orange)
Black = Ground
Green = Signal from SpeedoHealer to speedometer
White = Signal from speed sensor to SpeedoHealer

Pic#9 Finished splice.

At the glove box end, I plugged harness into the SpeedoHealer and used the included Velcro patch to attach the SpeedoHealer to the ac duct. It is easily accessible and out of the way.

Pic#10 SpeedHealer mounted

Now it was time to see if it worked.

I grabbed my GPS receiver and headed out in the Jeep to determine the exact speedo error. After verifying the correct speed v/s the speed displayed on the speedo, I used HealTech’s online (or downloadable) calculator and entered my actual speed v/s the displayed speed @ 60 miles per hour. HealTech also provides a formula in the instructions to allow you to calculate the correction value by hand. The calculator gave me a percentage of correction to enter into the SH-V4. It took a couple of minutes to understand the instructions for entering the value, but once I read the instructions for the second time and followed them, I had no trouble entering the correction value.

I have been running the SH-V4 for a few weeks now and it is working flawlessly! My speedo now matches my GPS speed readout.

By the way, the Top Speed Memory works like a champ. Plug in the harness with the push button on the end and press the button. The speedo dials up and shows the top speed that you have traveled since the top speed was reset. It holds the speed for about 3-4 seconds and then drops back to zero, or whatever speed you are actually traveling.

Here I am in my garage showing 80mph on my speedo.... Too fast for a TJ.

Pic#11 80mph

After this photo, I unplugged the top speed switch and put it with my other extra Jeep stuff. I don't intend to use this switch, but wanted to see if it really worked...

I am very happy with the SH-V4 and highly recommend it to anyone who wishes to correct the speedo readout on an electronic speedo such as the 2004 Rubicon has.


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