Speedometer Calibration (Updated Question)

EJ Husker · **Posted:** Tue Apr 22, 2008 4:09 pm

I recently put bigger tires on my 2005 liberty and I want to recalibrate the speedometer. I thought you could take it to the dealer and have the cpu reprogrammed, but after looking at it for 20 minutes and calling chrysler, they said its not possible with 2005 models. :roll:

So in my search, I find the Superlift TruSpeed. But they say they don't have a module for 2005 libertys only 2002 and 2003.

Are 2003's and 2005' that much different?? Anyone have a FSM that could compare? If the wiring is same it should work, right?

This is really driving me nuts :evil:

I saw another product Dakota Digital (I think) but it was not to be used with ABS, which I have on this 05.

Anyone help!

Ethan

raceinfan · **Posted:** Tue Apr 22, 2008 4:33 pm

what size tires did you put on ??????

my 245/75's throw off the speedo 2 miles an hour

my 245/70's throw it off 1 MPH

I tested it with one of those police trailer things that tells you your speed

I wouldn't worry about it, but thats my opinion

Jeep Dawg · **Posted:** Tue Apr 22, 2008 4:37 pm

I passed by 5 of thoes speed things yesterday after putting on my new 245/75/16 and I have a 2mph differance from all 5 speed things.

Jeepjeepster · **Posted:** Tue Apr 22, 2008 4:55 pm

My GPS says its off around 1mph depending on my speed.

the wife's · **Posted:** Tue Apr 22, 2008 7:55 pm

I went from the factory 215/85R16 to a 245/75R16 tire... According to my GPS, the speedo indicating 70mph I'm actually doing 73.5mph... About a 5% error. Checking the odometer over a 100 mile loop I've actually traveled 106 miles or, 6% error.

Clark

Pote · **Posted:** Tue Apr 22, 2008 8:08 pm

with my 245/70s when my odometer says I went 100 miles, I've actually driven 110. so for every mile I drive, its off one tenth of a mile and have actually driven .9 miles. When I'm driving 60 miles per hour on the speedo, I'm actually going 61 and a little change.

JL Rockies · **Posted:** Tue Apr 22, 2008 9:37 pm

Mine is off 5 mph @ 70 mph according to GPS.
I don't think the dealer can do much for me.

SavageUrge · **Posted:** Tue Apr 22, 2008 10:00 pm

My speedo reads 1mph faster with stock tires on

EJ Husker · **Posted:** Tue Apr 22, 2008 10:00 pm

The stock tire was 235/65/17 (29") and I put on 235/75/17 (30.9") I am about 6.4% off on the speedo and odometer. We clocked it over the weekend and when the cruise says 65 we really are driving about 69.5.

I am stickler I guess and want an accurate speedo.

Anyone have any thoughts on the Dakota Digital product?

Thanks for the replies.

Ethan

Rush345 · **Posted:** Wed Apr 23, 2008 12:52 am

I have 235/70-16 Dunlop Rover A/T's since installation I have seen in the Speed trailers that my Speedo is off and after installing a ScanGuage series I I have also noticed that the Speedo and the ScanGuage don't agree luckily it's in my favor my Speedo read 2 MPH slower then I'm actually traveling. Since the trailer speed readers and the ScanGuage agree I tend to accept them as fact. :twisted:

cmohr · **Posted:** Wed Apr 23, 2008 6:21 am

My speedo went out about 6% to 8% or so,when I went from 235/70/16's up to 245/75/16's. I have the auto V6, but apart from the speedo being out, I thought I had dropped quite a lot of power from just changing wheel size. I was right, The speedo also lets the ECU know whats going on, and if the ECU gets the wrong input, it makes engine management decissions based on incorrect data. My Kj lost a lot of power, was unresponsive, used heaps more fuel, and even the auto played up a lot, changing gears inappropiately , hunting around changing up and down all the time, torque converter locking up at 1200rpm in overdrive at about 30mph,(yes thats right, it's not even supposed to let the auto go into O/D below about 38-40) all very odd and very annoying, UNTIL I had a "pinion reset" done, that is the recalibration of the speed sensor, and yes it is possible on an 05 its just that the 05 doesn't have the same degree of ajustment as earlier models. Earlier models ( I have an 04 )you actually key in a "Revolutions per Mile" into the ECU, later models from what I understand have a choice of tyre size in the ECU for the tech to choose from. After I had the "Pinion Reset" done, I had my old KJ back, gears held properly (didn't hunt aroundanymore ) heaps more power and torque, and, fuel ecomony was far far better. I personally don't really care what speed the speedo is telling me I'm doing, its just that so much of the engine management system also relies on that info to make fuel mix and timing decissions, and auto gearbox control. Call me mad, call me crazy, but, it made a world of difference to my KJ.

If you are getting similar symtoms try asking the Dealership to look up a "Pinion Reset" they might have more success.

EJ Husker · **Posted:** Sun May 04, 2008 9:42 pm

So, I got a Dakota Digital device and I tried to get it hooked up today. I got a switched power source off the radio and the ground for the unit went fine. However, I can't for the life of me figure out how the speed sensor works.

On the rear axle there are two wires, exactly the same color. One shows 12V and the other nothing when the switch is on. Which one sends the signal to the PCM??? The way I thought it should work is the 12V powered wire provide the power to the tone ring sensor and the other wire would transmit the signal back. Thus, I should splice in on the unpowered wire to hook up to the Dakota Digital device right?? :?:

Also, anyone else with this device can tell me which outputs and/or settings I should use??

Thanks.

Ethan

tjkj2002 · **Posted:** Sun May 04, 2008 9:51 pm

EJ Husker wrote:

So, I got a Dakota Digital device and I tried to get it hooked up today. I got a switched power source off the radio and the ground for the unit went fine. However, I can't for the life of me figure out how the speed sensor works.

On the rear axle there are two wires, exactly the same color. One shows 12V and the other nothing when the switch is on. Which one sends the signal to the PCM??? The way I thought it should work is the 12V powered wire provide the power to the tone ring sensor and the other wire would transmit the signal back. Thus, I should splice in on the unpowered wire to hook up to the Dakota Digital device right?? :?:

Also, anyone else with this device can tell me which outputs and/or settings I should use??

Thanks.

Ethan

The speed sensor on the rear end uses A/C voltage,not D/C voltage.When the tone ring tooth passes next to the sensor magnit it produces A/C voltage in which the BCM uses that A/C signal to determine speed,pulses per min.

InCommando · **Posted:** Sun May 04, 2008 11:01 pm

Can't a friendly dealer do a "reflash" on the current ECM rather than going with a piggyback or aftermarket controller?

I am about to change tire sizes and I am much more interested in any performance issues than speedo accuracy.

Speedo accuracy is notoriusly bad with some makes. BMW got busted a few years go for speedo's that suddenly read too fast past 100 mph. I think it I read it in Car & Driver. Cruisers have the speedometers stamped "certified calibration" and they have to be re-tested every so often to maintain accuracy for moving-clock violations.

pokefan · **Posted:** Mon May 05, 2008 1:55 pm

InCommando wrote:

Speedo accuracy is notoriusly bad with some makes.

Doesn't seem anyone else here had the same issue as me but I always thought I was going slow as **** when I had my stock tires on. I'd be going 80 down the highway and barely passing people. After I put on the 245/75's I felt like I was going slow. At about 75 I'd pass people at about the same rate. A couple months later I finally got my GPS and come to find out I was SPOT on with bigger tires. I don't know how far it was off with the stock tires but it was definitely off.

WoodysKJ · **Posted:** Mon May 05, 2008 2:08 pm

InCommando wrote:

Can't a friendly dealer do a "reflash" on the current ECM rather than going with a piggyback or aftermarket controller?

I am about to change tire sizes and I am much more interested in any performance issues than speedo accuracy.

Speedo accuracy is notoriusly bad with some makes. BMW got busted a few years go for speedo's that suddenly read too fast past 100 mph. I think it I read it in Car & Driver. Cruisers have the speedometers stamped "certified calibration" and they have to be re-tested every so often to maintain accuracy for moving-clock violations.

YES THEY CAN.

cost ya a few bucks and you have to know what to ask for.

EJ Husker · **Posted:** Mon May 05, 2008 10:10 pm

WoodysKJ wrote:

InCommando wrote:

Can't a friendly dealer do a "reflash" on the current ECM rather than going with a piggyback or aftermarket controller?

I am about to change tire sizes and I am much more interested in any performance issues than speedo accuracy.

Speedo accuracy is notoriusly bad with some makes. BMW got busted a few years go for speedo's that suddenly read too fast past 100 mph. I think it I read it in Car & Driver. Cruisers have the speedometers stamped "certified calibration" and they have to be re-tested every so often to maintain accuracy for moving-clock violations.

YES THEY CAN.

cost ya a few bucks and you have to know what to ask for.

So what is the trick? Is it this "Pinion Reset"? I'm clueless here on how this works.

I will try to call the dealer tomorrow again and ask specifically for this and see what happens. When I went in before I didn't know what to ask for and they said it was not adjustable.

tjkj2002 wrote:

The speed sensor on the rear end uses A/C voltage,not D/C voltage.When the tone ring tooth passes next to the sensor magnit it produces A/C voltage in which the BCM uses that A/C signal to determine speed,pulses per min.

I was using that setting in the Dakota Unit (input A/C) but it was not picking up a signal either way. So I called Dakota again. They said to use a wire coming off of the PCM #4 which I found and spliced. Come to find out tonight that is for the transmission, so that only made the vehicle shift wrong. So i reconnected the original wires and it works as before, but my speedometer is STILL OFF!! Aaaarrrrgggh! I'm getting tired of pulling wire and splicing connections, only to find out what I am doing isn't working right.

Thank you all for your replies. I'll get this figured out someday. Any more input would be much appreciated.

Ethan

tjkoen01 · **Posted:** Tue May 06, 2008 9:13 am

EJ Husker wrote:

WoodysKJ wrote:

InCommando wrote:

Can't a friendly dealer do a "reflash" on the current ECM rather than going with a piggyback or aftermarket controller?

I am about to change tire sizes and I am much more interested in any performance issues than speedo accuracy.

Speedo accuracy is notoriusly bad with some makes. BMW got busted a few years go for speedo's that suddenly read too fast past 100 mph. I think it I read it in Car & Driver. Cruisers have the speedometers stamped "certified calibration" and they have to be re-tested every so often to maintain accuracy for moving-clock violations.

YES THEY CAN.

cost ya a few bucks and you have to know what to ask for.

So what is the trick? Is it this "Pinion Reset"? I'm clueless here on how this works.

I will try to call the dealer tomorrow again and ask specifically for this and see what happens. When I went in before I didn't know what to ask for and they said it was not adjustable.

tjkj2002 wrote:

The speed sensor on the rear end uses A/C voltage,not D/C voltage.When the tone ring tooth passes next to the sensor magnit it produces A/C voltage in which the BCM uses that A/C signal to determine speed,pulses per min.

I was using that setting in the Dakota Unit (input A/C) but it was not picking up a signal either way. So I called Dakota again. They said to use a wire coming off of the PCM #4 which I found and spliced. Come to find out tonight that is for the transmission, so that only made the vehicle shift wrong. So i reconnected the original wires and it works as before, but my speedometer is STILL OFF!! Aaaarrrrgggh! I'm getting tired of pulling wire and splicing connections, only to find out what I am doing isn't working right.

Thank you all for your replies. I'll get this figured out someday. Any more input would be much appreciated.

Ethan

I understand your frustration. I bought the Jet version of what you have. Couldn't get it to work either. I hooked up my oscilloscope to the sensor to monitor the signal on each of the wires coming off the speed sensor on the rear diff. It was not an AC current, definitely DC. I could see the pulses coming from the sensor while driving, it was at best a 1 volt, saw tooth drop from 12v. Don't know if that will help you at all. Let us know what you find out.

EJ Husker · **Posted:** Tue May 06, 2008 7:33 pm

The next episode in my saga.

I called Dakota back today and explained what I tried, the tech didn't have an answer. I tried an wire on the PCM, the wires comming directly from the axle, a BCM wire...nothing. He was very helpful, but no solutions so I am sending the unit back. He said they would love to test a few things out directly if there was a Liberty available in Sioux Falls, SD. But I live a bit to far away to try that.

tjkoen01: If that is true about the speed sensor signal, then the Dakota Unit will not be able to read that.

One last try at a different dealer and I did find a nice section in the FSM on Page 8E-6 that clearly states on Non-ABS equiped models that there is a Pinion factor and it can be reset. I will give it one more try armed with that information. I'll try to keep this thread updated.

Thanks all.

Ethan

EJ Husker · **Posted:** Wed May 07, 2008 8:56 pm

Well I went back to the dealer that swore that there was not way to change the setting in a 2005. Well after they looked at the FSM info I brought, walla, there it is under a miscellaneous menu in the Body Control Module on their scan tool (you are right WoodysKJ).

The menu has about 6 settings for different tire sizes, but all are near the stock size and nothing bigger. But there is a setting to change the revolutions per mile as stated by many here. So He tries to input it in and hits enter. The computer decides it does not like the setting for 672 revs/mile and says it will be programed for 56 revs/mile. So the tech tries it again a few times and it will not even go back to the original factory tire setting.

Next he tries to update the program with a new one that is two generations beyond the 2005 program. He begins to upload and poof! :shock:

The computer kicks the scan tool out and wont' allow a new connection. Of all the things that can go wrong, its occuring on this darn thing.

Dealer is ordering a new computer as the existing one is fried now and I can't go anywhere for a while. Hopefully the new one will allow the tire size change. The dealer was very good and said they won't be charging me for a new body control module as they are the ones that screwed it up.

Thats all for now...thanks for reading.

Ethan

Speedometer Calibration (Updated Question)

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