Is the trip computer part of COMBI?

morgant · Post by **morgant** » 21 Apr 2015, 21:12

I have a '97 850 with a broken odometer (I'm sure it's just a broken tooth on the usual gear) which I will eventually get around to repairing. I've tracked my fuel use since purchase a few years ago, but have only been able to guess at my MPG. I've used a ScanGauge II on previous vehicles, but it's not quite in the budget yet, so am thinking of swapping out my clock for the a trip computer. I've researched reading mileage from the instrument cluster (a.k.a. COMBI, if I understand correctly), but I'm not quite sure where that data is stored. If I were to swap out the clock for a trip computer, would I lose my mileage or only the instrument cluster itself?

Post by **erikv11** » 21 Apr 2015, 23:03

Mileage is stored in the cluster, not in the trip computer.

If you swap in a trip computer it will log miles traveled, even though the odo gear is broken.

morgant · Post by **morgant** » 22 Apr 2015, 04:38

Perfect, exactly what I was hoping for. Thanks!

Of course, installing a trip computer would be the perfect time to fix the odometer gear, but I'm not sure I can coordinate getting the actual mileage read yet. Does not look like a particularly difficult project anyway.

mika · Post by **mika** » 22 Apr 2015, 08:23

FYI, Any 98/99 cluster (not sure about 2000) will be direct swap IF you want to want the digital cluster instead of your 850 one.

Otherwise, it is easy to repair your current cluster in a half day job....

Important things to note: I thought the mileage is stored on the ABS unit on a 97? So if your ABS is caput, your gear will not work.

To answer your questionYes, you can read the actual mileage quite easily.
How to read actual mileage for your 97
step 1: you need an OBD2 Bluetooth dongle from ebay/amazon. the cheaper the better (less than 10 bucks)
step 2: get the app " ElmBasic " for android/google play
step 3: connect dongle to your phone and run this command:
>ATZ
>ATL1
>ATE1
>ATSP 3
>ATH1
>ATAL
>ATKW0
>ATTA 13
>ATRA 13
>ATIIA 51
>ATWM 82 51 13 A1
>ATSI
>ATSH 84 51 13
>B90300

voila, you have your (probably) accurate mileage, considering your ABS never went out.

this one works too and is shorter:

>ATPC
>ATIIA 51
>ATWM 82 51 13 A1
>ATSI
>ATSH 84 51 13
>B90300

more info than you will ever need:http://jonesrh.info/volvo850/elm327_rea ... leage.html

Lastly: once you get the original mileage, you will need to correct your mileage counter since it is off. How to do this? You will use an electrical drill with a Philips head to turn the counter forward..... To do this, there is a motor connected to the odometer counter, and it has 2 tiny Philips screws. Use one of the Philips screws to "thread" it into the old odometer gear (the larger of the 2 gears) this way you can use your electric drill to turn the assembly easily. (took me 2 hours to correct 45k miles) Pictures to follow on this last step if you want.

Step One: purchase both odometer gears and OBD connecter. Find actual mileage

Forgot to mention: Points after doing this repair myself
1) before reinstalling everything, make sure the counter spins freely with your hand. Even with motor connected it should rotate/gain mileage if you spin the cog by hand.
2) don't reset trip meter while driving in the future, it can ruin the odometer gear.
3) when fixing odometer, make sure the decimal part of the trip meter .1 miles .2 miles, ect, is in sync with the odometer: example: when your trip meter reaches .9, and then onto .0, it is at this point where the odometer mileage changes. I don't know how else to explain it. When I fixed mine, the trip counter is out of sync with the odometer, so mileage changes when trip counter is at .6 instead. Not in sync.

Blockpartie · Post by **Blockpartie** » 22 Apr 2015, 08:50

mika wrote:FYI, Any 98/99 cluster (not sure about 2000) will be direct swap IF you want to want the digital cluster instead of your 850 one.

'99 doesn't work

Post by **erikv11** » 22 Apr 2015, 09:08

Also, 96-97-98 all have the same ABS unit, mileage is not stored there.

morgant · Post by **morgant** » 22 Apr 2015, 11:15

I was pretty sure the mileage wasn't stored in the ABS unit (plus, I already had that swapped out). I personally don't want to swap out my instrument cluster to the digital version, esp. if it'll mean losing my mileage.

I've definitely read through all of Richard Jones' Volvo 850 OBDII site and the related threads here and am aware of what's required to repair & set the odometer, though it doesn't hurt to repeat it.

mika · Post by **mika** » 23 Apr 2015, 07:44

let us know how it goes. Nice to have a working odometer, especially an old school "rolly" one instead of digital.

Post by **esl_97_850_T5** » 27 Apr 2015, 23:51

Most everything stated seems to be true or has already been corrected. Here's my 2 cents of repetitions and clarifications.

1. 96-98 850/S70/V70/XC70 ABS does not store the total vehicle mileage. Those cars' COMBI microprocessor stores the total vehicle mileage in whatever form of EPROM/flash memory that the microprocessor contains or is connected to. Their Trip Computer (if used) is a separate entity from the EPROM/flash memory. The Trip Computer is written to by the COMBI microprocessor (as I understand it), but the Trip Computer does not store the total vehicle mileage. However, the Trip Computer can store a 9999 mile or 9999 km subset of the total vehicle mileage before it rolls back to 0.0.

If 96-98 850/S70/V70/XC70 ABS is not supplying the vehicle speed signal to the COMBI properly, then all 4 mileage recording indicators -- COMBI's B903 (total vehicle mileage / 10) stored data, 850's mechanical odometer, S70/V70/XC70's digital odometer, and trip computer (if used) -- can be expected to lag the actual mileage, since (I think) all of them derive the mileage from the vehicle speed signal supplied by the ABS either directly (or indirectly via the COMBI microprocessor).

So it is true that if the ABS is caput with respect to supplying a vehicle speed signal, then the odometer gear will not turn. But in that case the reason that the odometer gear is not turning is not because the ABS is not supplying the total vehicle mileage (which the ABS does not even know about), but because the ABS is not supplying the vehicle speed signal which the COMBI then uses to computer the mileage.

2. The shorter method that mika mentioned -- the one involving 5 ELM327 commands that start with ATPC and 1 KWPD3B0 request that involves B903 -- generalized so it avoids 00-padding of B903 and therefore works with both '96-'97 850 and '98 S70/V70/XC70:

ATPC
ATIIA 51
ATWM 82 51 13 A1
ATSI [this is optional]
ATSH 83 51 13
B903

only works if it is preceded at least once by the most crucial special ELM327 commands which setup for KWPD3B0 communication:

ATZ
ATL1
ATE1 [or ATE0, depending on how your terminal emulator behaves]
ATSP 3
ATH1
ATAL
ATKW0
ATTA 13
ATRA 13

and those special KWPD3B0-enabling commands are not overridden by a power failure, cable disconnect, ATZ, ATD, or ATWS.

My point is you can't immediately jump from OBDII emission diagnostics (which can be started simply by ATZ / ATL1 / 0100) into COMBI KWPD3B0 diagnostics by issuing the short list (of ATPC / ATIIA 51 / ATWM 82 51 13 A1 / ATSH 83 51 13 / B903). If you had done that, you would have failed to issue several commands that are crucial for KWPD3B0 communication (ATH1 / ATAL / ATKW0 / ATTA 13 / ATRA 13).

I'm near certain mika knows that already, but it seemed the clarification might be needed for someone that is getting their first exposure to reading the vehicle mileage via this thread.

3. mika mentioned one of the ways to read the vehicle mileage via an ELM327 device -- using a cheap OBDII Bluetooth dongle from ebay/amazon along with the Android app "ElmBasic" available from Google Play. That's a good suggestion for someone with an Android device. But it is just one of the variety of ELM327 device / software combinations that work to read the '96-'98 Volvo 850/S70/V70/XC70 vehicle mileage. Some people have used other Android terminal emulator apps. Some people have used more expensive, more reliable ELM327 Bluetooth devices. Some people have used ELM327 USB cables -- both cheap ELM327 clone USB cables and ScanTool.net OBDLink SX cables. Some people have used Windows based terminal emulators, like STNterm, Realterm, Hyperterminal, etc. Some people have used volvo850diag. Some people have used WinXP. Some have used Win7. The list continues to grow.

4. I'd suggest elm327_reads_volvo_850_svc70_mileage.html as the better page to use as a reference, instead of the 850-specific elm327_reads_volvo_850_mileage.html page.

5. The trip computer will definitely log miles traveled, even though the odo gear is broken.

esl_97_850_T5

morgant · Post by **morgant** » 25 Sep 2015, 14:42

Well, I finally got to test this this evening. I had already swapped out my clock for the trip computer months ago, but was having issues getting my computer to communicate with my OBDLink S (turns out I had the baud rate incorrect, due to finding some incorrect documentation). My odometer had died at 125K or so, but read it as 218690 today. That makes sense for the mileage I put on it since purchase a few years ago.

Now I know I can disassemble the dash again and correct the odometer (for my own reference).