Calibrate the speedo

[Pottsy]

This article will show you how to remove the built in speedo error. The speedo over-reads by about 5% to 9%, so that any shape or variation in tyre size fitted will always show an over-read, so Honda can never get into legal problems if you are caught speeding when your speedo says you are not.

Difficulty:

Pretty easy. Nuts and bolts, bit of wire stripping and soldering. Should take about an hour.

Ingredients:

A Speedo Healer. This £57 device is a tiny little computer normally fitted to motorcycles that takes the pulses from the speed sensor, and sends slightly slower pulses to the car. It is a mature product, that works well and is transparent in operation.

Socket set, 10mm spanner, wire cutters, soldering iron and solder.

Instructions:

Firstly measure the speedo error using your preferred method. Make sure it's accurate! I used a collection of GPS readings, including the one shown on cars with satnav. I found that if using a flat road and cruise control to keep a steady speed, then it's best to use fourth gear (not sixth), to give the car better control of the speed.

sh_before.jpg

Take out the car keys and put them in your pocket.

Remove the battery clamp, the negative battery terminal and then the positive battery terminal. Lift out the battery using the handles and then pull out the plastic battery holder.

sha1.jpg

Remove the bolt that hold the air filter box to the battery support shelf:

sha2.jpg

Remove the 6 12mm bolts that hold the battery support shelf and whip out the shelf:

sha3.jpg

At the front of the gearbox you'll find the speed sensor plug and socket. The plug is released by pressing in a catch, and it can then be unplugged.

I also unclipped the little bit of loom to allow me to get the plug nice and high for soldering work.

sha4.jpg

Trim back the loom black tape and tube, and then cut the blue/white wire (blue/black on 1.8 cars).

shb1.jpg

The Speedo Healer (SH) comes with its own 4 wire loom. Strip off the red casing for most of the length and leave the red and black wires. Shorten the green and white wires so they will go from the socket on the gearbox to the place you are going to mount the SH.

Put a heat shrink tube (included) onto both the green and white wires.

Strip the two ends of the blue/white wires - solder the SH green wire to the end that goes to the loom, and solder the SH white wire to the short end that goes to the speed sensor plug.

Shrink the tubes over the joints (using a lighter) and tape the whole area up again.

Plug in the plug.

shb2.jpg

Attach the black wire on the SH loom to a suitable earth. I shortened the wires, tinned the end and when putting back the battery support shelf, used one of those bolts:

shb3.jpg

Open up the fuse box and pull out the grey relay shown.

It's tricky to remove. You mustn't use pliers, because these may damage it. Just use fingers, and pull it out while rocking it a bit.

Poke the red wire from the SH loom into the bottom right hole (trim the wire a bit, and make sure no strands poke out - the wire mustn't interfere with the other relay connections) and push the relay back in.

shb4.jpg

Fit an inline fuse to that wire, and cut a little exit hole for it in the fuse box:

shb5.jpg

I then attached the SH to the front of the air filter box using the supplied velcro (having degreased the surfaces). It's good to have the velcro and a bit of spare wire, so you can move the SH for easier programming.

shb6.jpg

Next, use the online calculator to generate instructions on how to program the SH.

Go for a drive! I can see no difference in the operation of the car speedo, except that it's now accurate.

Notes:

This how to has been done on a diesel - the 1.8 may be slightly different.

SH recommend keeping the SH wires away from other loom wires, and mounting the SH away from other electronics.

It's probably best to recalibrate every time you change your tyres. Different tyres (even of supposedly the same size) will in fact be different sizes.

As a tyre wears, the speedo will start to over-read. From new to worn, this change corresponds to 1 mph total at 70 mph.

Because you are removing (say) 6% of the speed pulses, your odometer will accumulate miles at a rate reduced by 6%, and your mpg readout on the computer will also be reduced by 6% (and will probably end up being accurate!!)

Speedo Healer: distributors, bike tutorials, testimonials.

And thanks to Norbert at Speedo Healer for his great help in researching and helping with this little project.

[druidh]

Why?

[Jack The Lad.]

Gordon Bennett Pottsy, you are one clever s-d.
Would you care to spend a weekend at our place, doing the business on mine.
"Er Indoors" will keep you well fed and I will keep you well p-ssed at our local.
If you find you have an extra 10 minutes, you could do me rear parking sensors as well.

[Foggy69]

Originally Posted by Pottsy

I don't actually know how accurate the odo is. Most cars over-read (have a look at the specs at the bottom of this page), and there appears to be no legally required standard. So it doesn't really worry me - and I don't think the difference will make a real variation in value of the car at sale time.

Also, have a look at this....

Aaahhh, the bug-eyed Impreza, a great car and ugly as sin. (Sorry going dewy eyed over my old car)

Right back on topic
Do you want a 1.8 i-shift to practise on as well

[TTDegs]

Pottsy, sir, with all the other things going on, I have absolutely no blinking idea how you find the time to do these things

But I'm very grateful that you do!

[Pottsy]

This really is an easy mod. Did it in about an hour this afternoon, then went for a curry, then posted this thread. Will post about the other stuff tomorrow..

Would recommend this mod very highly. It is much more relaxing being able to see your actual speed, and not having to constantly do mental arithmetic to work out your speed.

[robbo51]

Great Job Pottsy but I'm going to use my Talex which I know is accurate.
One I can remember is Speedo 44mph.....Talex 40mph

[Bog]

Originally Posted by Pottsy

This really is an easy mod. Did it in about an hour this afternoon, then went for a curry, then posted this thread. Will post about the other stuff tomorrow..

Would recommend this mod very highly. It is much more relaxing being able to see your actual speed, and not having to constantly do mental arithmetic to work out your speed.

Other stuff?

There you go again dangling carrots

[Pottsy]

I've put odometer comments here:

Odometer accuracy

[TTDegs]

Originally Posted by Bog

Other stuff?

There you go again dangling carrots

but possibly only for the newly Mrs Civinfo

[Alwaysblack]

Pottsy.
I think you stole the pilots uniform.
You obviously fix the *******g things, not fly em!

[philosoma]

I have ordered one of these to stop me always looking at the satnav speed. Hope CTR is not too different from your guide.

Silly question, but what would happen if the unit failed while driving? The speedo would go dead I guess, but would the ECU throw a spaz and do damage?

And the wire that goes in to the relay is just for 12V power? Thanks

[prawncracker]

Why go through all the hassle.
Just use a satnav once and you'll be able to tell how far out your speedo is. It's just a certain speeds you'd need to remember - 30, 40, 50, 60, 70, and of course 20mph for damn school zones

[Selwoc]

I've just fitted the SH to my Civic, it really was as easy as Potty said. The only problem was needing three hands to hold the wires, the soldering iron and the solder. All done in under an hour.

It was odd to overtake another Civic at night on a duel carriage way, I could see his speedo reading 52, mine was on 51

[vivid bluey]

I just used my satnav if i need an accurate speed. We all drive a little (!!??!!) over the limit so if the speed o is reading a little over isn't that better? If it's accurate & you're over then you're well over!!!

[Billybobbo]

Has anyone managed to do this on the 1.8 yet?
I'm really struggling as the battery support is not like the 2.2 - it cant be removed from above as there are two bolts on top and two down the side, one of which is impossible to reach unless I jack up the car and go at it from under the car.
Suffice to say it wont take an hour to do - more like a day the way things are going and I really don't know if I can be as*ed!

[vivid bluey]

I've checked my speedo against my satnav, Indic8tor & road speed warning signs & it's 4mph over at severeal different speeds, so all I do is deduct 4mph from the speedo reading. Is 4mph over that critical? I'll use the speedo reading knowing that I'm slightly under that I think !!!

[kenP]

I can't really see the point.

[ctrdaveg]

Surely sat-nav speeds are not that accurate ??

[Unknownsoldier]

More accurate than the Speedo.

Tom