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Joined: Nov 02 2020
Posts: 7

Hi All,

I have just bought a new cluster as I broke the fuel needle trying to clean it. I saw on Facebook that a chap found that when be plugged a new cluster in it reverted to the mileage on the cluster and not his actual mileage. Is that correct?

Is there any way of changing this? I would have thought the mileage is set by the ECU and not the cluster?

Tom

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Joined: Dec 30 2015
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Mileage is stored in both the cluster and the BeCM and it will initially show ODO Error on the dash, then it will change to read the higher of the two but not change until you use a Nano or similar to sync them. It won't allow you to show the lower of the two readings no matter what, only the higher one. If you swap the actual clocks but retain your original circuit board and display, then it will work as normal.

There's a lot of people on faceache that think they know what they are doing then are stupid enough to not only do something stupid but even post about how stupid they've been. As you probably guessed, I don't like facebook or the stupid people that use it......

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Oh yes, and the clock displays will probably read differently too as each circuit board is calibrated to the individual instruments, so your speedo, tach, temp and fuel gauges will probably read slightly differently unless you re-calibrate them.

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Joined: Feb 25 2020
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Welcome!
Besides all what written correctly above, what sounds like an abomination is actually how most vehicles of "modern making" do track odo readings ... some of them even track it on the keyfob, which is now much more than a mere remote :-)

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Joined: Jan 16 2017
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Some VW vehicles store the immobiliser data on the instrument cluster, which is far more annoying. And they do the same thing with the odometer reading as described above as well. Having swapped one over in a Golf for someone who managed to fry his old cluster by repeatedly jump starting the car (at least thats what suspected to have done it, maybe it just failed for some other reason) I can confirm thats definitely the case (and it won't start without some work with VCDS and VAG-Tacho in that case either)

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Joined: Nov 02 2020
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Bugger! but thanks for the information. Can the mileage be altered at a dealership with the special LR diagnostics tool?

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Joined: Dec 30 2015
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No, it can't be done. But like I say, you can swap your circuit board and display and fit that to the replacement clocks. The errors will only be slight and you can calibrate the replacements to make your clocks read correctly. I swapped the main pcb on mine (as one of the MOSFETs that drove some of the warning lights was dying) but kept the original clocks and display so the mileage didn't alter but the speedo and tacho had to be recalibrated and the temp gauge needle reads slightly higher than it used to.

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Joined: Nov 02 2020
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How difficult is it to complete a switch over? Is any soldering involved?

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Joined: Dec 30 2015
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No, no soldering. Lots of small screws though. But, if it's only the fuel gauge you have damaged, there's nothing to stop you from simply swapping that over from one cluster to the other. 3 screws attach it to the PCB and possibly a couple more that keep it in place.

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Joined: Nov 02 2020
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Great thanks!

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Unplug the speaker on the back, pop the translucent cover off the back and you'll see the 3 screws that hold the actual gauge to the board. Pop the clear screen off the front and then the same with the black plastic surround. That will expose the gauges. If you managed to break the needle off the fuel gauge you've obviously been this far anyway. Undo the 3 screws that secure the gauge to the pcb and it should just drop out. Swap it over and put it all back together.

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Joined: Dec 22 2016
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Shameless plug: If desperate, I can update the mileage on cluster and or BECM. :D

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Joined: Nov 02 2020
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What sort of voodoo magic allow you to do so?

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Joined: Mar 22 2016
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tking88 wrote:

What sort of voodoo magic allow you to do so?

😂🤣😂🤣

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OK, so I threatened to do it and Tom talked me into it, so here goes:
Pulling an instrument cluster apart.
Primarily on how to swap one of the gauges (in Tom’s case, the fuel gauge) but would apply to any of the internals really. If you don’t know how to get the instrument cluster out, drop the knee panel, undo the 4 screws (two at the top, two at the bottom obscured by the knee panel) that hold the instrument panel surround and as you lift it out, unplug the connector to the fuel flap release. There’s 2 connectors to the bottom of the instrument cluster. With ignition off and the key safely inside the house, unplug these two connectors. There’s a screw in each corner that secures the instrument cluster but they don’t have to be fully removed, just unscrew them until the instrument cluster is free. Once all 4 are free, lift the cluster out.

To take it apart, completely remove the 4 screws (as they also hold the front and back together), unplug the connector to the speaker marked 1 (which is what gives you the annoying beeps as well as the tick, tick from the indicators) and using a fingernail, unclip the translucent back cover at the points marked 2 along with one on each side.

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Hinge it upwards (there’s another fixing in the centre that will pop out) and it will come off (and tear the security seals along the top) and expose the main pcb with the ribbon cable going to the display. So you’ll see this:

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Notice the 4 groups of 3 screws (circled in red), these are what hold each of the individual gauges in place and also provide their electrical connections. Loosely sit it on the translucent cover and turn it over. On the top you’ll see two black lugs which will pop open if you press in with your thumb and push it out and you can hinge the whole front out.

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The front is in three parts, the clear outer, the black surround and a plate that goes around each gauge. With that off you are left with the white plastic body with everything attached. If you want to change one of the gauges you just undo the 3 screws that hold it to the pcb and out it comes.

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The mileage information is held in one on the chips on the main pcb, so as long as you retain that, everything else can be changed. I know there’s at least 3 different style of gauges, some have graduations every 2 miles on the speedo, some every 5 miles and then there’s the ones fitted to later cars with a dark green background rather than black as on the earlier ones. There would be nothing to stop anyone swapping all the gauges and the message centre display as long as you keep the original main pcb. If you were to swap the main pcb and it has a lower mileage than is stored in the BeCM, then the mileages can be synced but be aware it will always take the higher one of the two. So if you’ve got a low mileage car and you get a spare panel from a higher mileage car and swap the pcb, your mileage will suddenly shoot up. Incidentally, the BeCM only stores to the nearest 100 miles too, so if your BeCM says you’ve done 125,800 and your dash says 125, 870 and you sync to a lower mileage pcb, you’ll lose 70 miles (so don’t do it just after the MoT).

Putting it all back together is just the reverse of taking it apart but be aware when refitting it that there are lugs that fit into holes next to the screws that hold the cluster in place so you need to wiggle it about a bit to make sure they slot in place. Don’t forget to plug the speaker back in either. Don’t turn the ignition on with the instrument cluster out or unplugged (hence the warning about leaving the key in the house) or you’ll be dealing with SRS, and possibly dashboard, faults.

Calibrating the gauges.
While you’ve got it out, you may as well calibrate the gauges if you are really sad. The BeCM sends a digital signal to the cluster which uses digital to analogue converters to drive the gauges. As they are electromechanical, there can be differences from one to another so if you were to swap a gauge you might find it will read slightly differently to the old one. With the instrument cluster out, break the yellow paper seals so you can remove the translucent plastic cover (which will also mean unplugging the speaker) and if you look along the top of the circuit board you'll see a row of three blue trimmer pots on each side. These are used to calibrate the gauges.

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On every P38 I have driven except my ex-plod with a calibrated speedo, they all read over so an indicated 70mph is usually a true 65-67 mph (for type approval purposes and speedo can legally over read by up to 10% but cannot under read at all). To calibrate the speedo you first need to know how far out it is, by how much and in what way by comparing the speedo reading against a sat nav. Remember that the GPS on the sat nav will only be 100% accurate when travelling at a constant speed on a flat, straight piece of road.
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If you have a GEMS and a Nanocom (it may be the same on a Thor but I don’t have one to try it on) that makes it very easy as in the ABS menu there is a setting (ABS- Diagnostic-Utilities-Speedo) that causes the speedo to read around 50 mph (Nanocom documentation says it will make the speedo read 100 mph but on all that I've tried it on it reads about 50 mph). So you can set that, make a mental note of what it reads, then drive holding your speed at that same point and compare your actual speed on the GPS compared with what the speedo says. Then drive at different speeds and check them against the GPS so you have an idea of how far out it is at different speeds. You’ll now have your baseline figures so can adjust from there. The trimmers you need are marked VR3 and VR4.

VR4 deals with Offset and adjusts the reading by the same amount over the full range. So if it permanently reads 5mph over, then you adjust that with VR4. It is pretty rare for the offset to need to be adjusted. VR3 deals with slope so if it reads OK at 20 mph but the error gets progressively greater the faster you go, adjust the slope until it is correct over the full range. With the instrument cluster surround out, the cluster itself in place but not screwed in and the translucent cover partly loose, you can get in there with a very short trimming tool (I used the screwdriver bit from a set of the interchangeable bits) but be careful as you only need to give the pots a tiny bit of movement (many years of tuning radio transmitters for maximum power means I've got pretty good at it). On a GEMS, once you’ve seen where the needle sits when driven by the Nano all you need do is use it to drive the speedo to the figure and adjust VR3 so the needle is reading what your actual speed was at that reading.

If you feel like having a play while you are in there, VR1 deals with the Temp gauge reading, VR2 the fuel gauge reading while VR5 and 6 do the same as 3 and 4 but on the rev counter (can't remember which is which though but you have the same offset and slope adjustments on those two). Bear in mind that the fuel and temp gauges are fairly heavily damped so won’t respond immediately to any adjustments.

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Joined: Sep 12 2018
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Wow!

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Joined: Aug 05 2019
Posts: 158

Fantastic, well done!

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Joined: Dec 03 2019
Posts: 47

Great, thanks. even I shouldn't have any trouble with that guide

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Joined: Dec 30 2015
Posts: 1217

As long as you're careful then they are easy enough to pull apart - I have done loads of them to LED convert them etc.

I also have the tools to reprogram a cluster mileage and the BECM mileage. It's just a case of having an EEPROM programmer for the cluster, and knowing what format the mileage is stored in.

The BECM can be reset a couple of ways, but I won't post that on an public forum ;)

But needless to say, it's not the doom and gloom that a lot of people make it out to be. It isn't the easiest task, as it requires some de-soldering of the chip in the cluster - but I've done a few mileage corrections for people over the years who have been told it's fine to just swap the cluster, and then wondered why their mileage suddenly spiked!

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Joined: Nov 02 2020
Posts: 7

Awesome guide and thank you Richard.

Question - how do you adjust the calibration blue things you mention. Are they knobs or dials of some sort?