Playing with the OBD-ii... got the mileage?

takane2 · Post by **takane2** » 24 Mar 2010, 09:03

So I have a check engine light on my recently purchased '97 850. It came on after i bought the car not during the test drive of course

. Anyway I rigged up that circuit to get blink codes from the obd-ii. The pinout on volvospeed didn't work(ie pin 3 was not the diagnostic computer) so i tried some others. I got my fault codes from pin 7 which match what the guy from autozone got from his generic code scanner(He got mixture too rich, I got 231 and 122) But I had this crazy idea that since the dash's port on a obd-i was A7 and I was connected to pin 7 I tried the procedure to get the mileage and it worked! I think, what I got was 154,689 which was higher than what the previous owner or the carfax reports said. My odometer is busted so I can't tell for sure. Can someone else with odb-ii try it and see if it matches you odometer?

Post by **MadeInJapan** » 25 Mar 2010, 17:27

Could you post a picture of your gizmo as well as which pins you hooked up to.
I'm curious and if this works like it seems it's working, this is a great find and should work for the '98 S/V/XC/C 70's too!

takane2 · Post by **takane2** » 26 Mar 2010, 15:05

: obd.PNG (2.77 KiB) Viewed 10073 times

R1 should be whatever is closest(round up):

Code: Select all

 (12v - Vf)/If

Use your LED's datasheet to find the Vf at an appropriate forward current.
But for a standard red LED 1k should be fine.
I originally had a additonal1k in series with the switch to ground to limit the current since I am unsure how the OBD-ii input circuits work. I ended up not using it because I was originally trying to get this to work with pin 3 as I had read that this was the correct pin elsewhere, and wondered if it the reason why things were not working was because the 1k was not allowing the OBD's input to be pulled down far enough. I never tried reconnecting it after figuring out that i needed to use pin 7.

Pin 5 is ground.
Pin 7 is the diagnostic pin.
Pin 16 is +12v.

Post by **VCA** » 27 Mar 2010, 22:02

MadeInJapan wrote:Could you post a picture of your gizmo as well as which pins you hooked up to.
I'm curious and if this works like it seems it's working, this is a great find and should work for the '98 S/V/XC/C 70's too!

Wow, cool. Yes, this should work on '98 S/V/XC/C 70's. Do NOT try this on '99s and newer and on '98 S80s...pin 7 is the accessory Class II serial data (LIN) line...and you will likely cause stress to if not toast quite a few modules.

Post by **MadeInJapan** » 28 Mar 2010, 06:35

Thanks for posting this. I will pin it...I know there was another thread about doing the home-made scan tool for 850's and first gen 70 series and it would be great to pair these two.... Oh, well, I'll figure it out.

takane2 · Post by **takane2** » 28 Mar 2010, 15:03

zwolf7 wrote:Some questions, I see the formula for the R1 is (12V-Vf)/If, and if I understand this is 12 volts minus the diodes Vf spec. Then divide by If, but I'm at a loss for If. Please explain. When you get your figure, use whatever is closest, round up for R1's value. You mentioned that you tried the "procedure" and it worked. Please explain the procedure, for the slow children such as myself. Thanks.

If is the forward current. The Vf will be dependent on this. The purpose of having a resistor in series with an LED is to limit If. If If is too high you will smoke the LED, too low the LED won't light much if at all. You only really need that equation if you are using some weird LED like a super bright. For your standard red LED you can just use a 1k resistor.

As for the rounding up, resistors are only manufactured at specific values so you should round up to the nearest commonly manufactured value and use that.

Here is the procedure I mentioned.

takane2 · Post by **takane2** » 31 Mar 2010, 07:21

Anyone with a working odometer tried this yet so we can confirm that this is indeed the mileage?

I hope to eventually try and figure out the protocol more, see if I can change/determine what control I have selected/where I am getting the DTCs from etc.

takane2 · Post by **takane2** » 12 Jun 2010, 08:09

I am taking the cluster out to fix the gauge alignment my mechanic screwed up and do a few other things and figure I should get the odometer too. I just checked the mileage again with this and it increased my a reasonable amount so I believe I can indeed state that this is the mileage that is being read(and the previous owner is a lair :p)

Rich85GTS · Post by **Rich85GTS** » 28 Jun 2010, 11:09

Hello,
I found your post very interesting. My 96 850 Volvo's analogue odometer stopped working last fall so while fixing it I installed a junk yard Volvo 850 Instrument panel into my 850 for temp use. A local Volvo dealer coudn't read the ECU/Instrument panel ODO mileage from this Junk yard one, but could read digital odometer mileage with their Volvo scan tool when I reinstalled the "original " Dash, now with a fixed analogue odometer. It sounds from your post below that you were able to read your odometer mileage direct from your under-the-hood ECU pin outs. I'm trying to figure out if my 850's ECU retains mileage info as well as sending it for storage in my instrument panel. The local Volvo techs all tell me it's just stored in the Instrument panel. It makes more sense to me that, as with pre-96 models, it is still stored in the ECU even though also in Instrument panel. Would you happen to have tried reading mileage direct from your ECU pins without your Instrument panel connected?

""But I had this crazy idea that since the dash's port on a obd-i was A7 and I was connected to pin 7 I tried the procedure to get the mileage and it worked! I think, what I got was 154,689 which was higher than what the previous owner or the carfax reports said. My odometer is busted so I can't tell for sure. Can someone else with odb-ii try it and see if it matches you odometer?"""