Speedo error

sssagiledriver

New member
Has anyone had any luck trying to correct the speedometer error? My T1N/Roadtrek Agile reads about 5 mph fast at 65 (actual speed 60).
 

Altered Sprinter

Happy Little Vegemite
it should be 5 mph less not advanced.
MB has a specific built-in error of margins 10% - and 10% + [A]..because of electronics, and ..as to varying tire sizes and or dimentaions.
Hence as an example your trip meter is 99.999999% accurate.
Richard
 

OrioN

2008 2500 170" EXT
it should be 5 mph less not advanced.
MB has a specific built-in error of margins 10% - and 10% + [A]..because of electronics, and ..as to varying tire sizes and or dimentaions.
Hence as an example your trip meter is 99.999999% accurate.
Richard


If they are smaller diameter it will read higher.
 

OrioN

2008 2500 170" EXT
He could be running 13" and hydraulic suspension and the van was featured on Pimp My Ride for all we know. :bounce:


BLING!
 

autostaretx

Erratic Member
You've got a number of quick/simple ways to "correct" the speedometer:
(a) if you have 15" wheels, upgrade to 16". Then the speedo will be accurate (but your odo will be off... think "longer warranty")
(b) buy a ScanGauge (or equivalent)... the MPH *it* reports is spot-on accurate.
(c) install a GPS, which also can provide accurate speed reports.
(d) add an accurate scale to your existing meter (stick-on marks for the cardinal 30/40/50/60/70)

I use (b) and (c).
--dick
p.s. for what it's worth, my new Kia also reads "faster" than i'm actually travelling. It gets (c).
 

OrioN

2008 2500 170" EXT
I up sized my tires. Now over 1.25" larger in diameter. (Point the stock sized Contis were 0.5" smaller than the Michelin equivalent). My speedy now says I'm going 5-7mph slower than I am. The MPG meter now tells me I get 15% less MPG's.

My dishes rattling in the sink tell me what speed I'm driving, the change left in my pocket tell me how many miles to gallon I got.
 

Altered Sprinter

Happy Little Vegemite
I up sized my tires. Now over 1.25" larger in diameter. (Point the stock sized Contis were 0.5" smaller than the Michelin equivalent). My speedy now says I'm going 5-7mph slower than I am. The MPG meter now tells me I get 15% less MPG's.

My dishes rattling in the sink tell me what speed I'm driving, the change left in my pocket tell me how many miles to gallon I got.
You need help:smilewink: and I thought I had issues.:lol:
 

rvdriverca

New member
Has anyone had any luck trying to correct the speedometer error? My T1N/Roadtrek Agile reads about 5 mph fast at 65 (actual speed 60).
But nobody has answer this persons original question. this is typically what happens when Richard gets in there. Richard everybody knows different tyres sizes at a set speed, turn at different RPM"s. This person wanted to know if there is a calibration for the speed-o-meter, screw the tyres.:bash:
 

OrioN

2008 2500 170" EXT
Yes Richard quite right.
The answer to the question ! yes it can be done.
2 no it can not be done
OUCH!

If he didn't swap tire sizes, the answer is NO.
If he did, and the size is one of the available selections in the ECU, then the answer is YES.

Let the OP respond.
 

Altered Sprinter

Happy Little Vegemite
Agreed let the OP respond..first poster as usual.
Take the factoring of tire equations out of it, no one has yet shown on the forum an accurate reprogramming from MB for exacting match of MPH to the actual speedometer reading that I am aware of.
On the NCV there are specific reprogramming sequences available under the body builders portal manuals for Euro Sprinters only.
This is for telma transmission generators on manual transmissions only not auto not a V6. Under the PSM module for both digital and analog programing via the can bus, edc for signal acquisition via DAS menues.
Both Tin and NCV require the final code from MB for activation.End of story .
This is not a program available to NAFTA MB USA vans which is why JD gets the grumps up I guess.
Richard
 

autostaretx

Erratic Member
The problem is that the "programming" would have to be done in the instrument cluster (although somehow tweaking the meter itself may work) or the CAB (see below).
To quote the T1N service manual:
The speedometer consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 210 degree primary outer scale on the gauge dial face that reads left-to-right either from “0” to “100” miles-per-hour, or from “0” to “180” kilometers-per-hour, depending upon the market for which the vehicle is manufactured.
...
This gauge is controlled by the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Controller Anti-lock Brake (CAB) over the Controller Area Network (CAN) data bus. The speedometer is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board when the instrument cluster detects that the ignition switch is
in the On position. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the Off position. The instrument cluster circuitry controls the gauge needle position and provides the following features:
* Vehicle Speed Message - Each time the cluster receives a vehicle speed message from the CAB it will calculate the correct vehicle speed reading and position the gauge needle at that relative speed position on the gauge scale. The gauge needle will continue to be positioned at the actual vehicle speed position on the gauge scale until the ignition switch is turned to the Off position
..........
The CAB continually monitors the four wheel speed sensors to determine the vehicle road speed.
The CAB then sends the proper vehicle speed messages to the instrument cluster.
For proper diagnosis of the wheel speed sensors, the CAB, the CAN data bus, or the electronic message inputs to the instrument cluster that control the speedometer, a DRBIIIt scan tool is required. Refer to the appropriate diagnostic information
So the CAB sends the message, and the Instrument Cluster processors move the needle.
Since ODB-II readers like the ScanGauge report the *correct* speed, it's still unclear (without monitoring the CAB messages) which device is making the speedometer read high. At least it's probably not the ECU.

--dick
 

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