A friend of mine brought up an interesting point about car accidents and it prompts this question:

On an OBD I 1993, is there any way I could extract the Vehicle Speed Sensor data (want to know speed car was going, exactly) from the very last time the engine was running? I thought that stuff was erased when you turn the motor off, not permanently stored in the ECM or Prom chip.

Thanks

 

It isn't "erased when you turn the motor off", because it is never saved anywhere in the first place. The data is used "on the fly", then it's gone. Unless you had some sort of data logger or aircraft type of "black box" hooked up, the info was only available as it was being generated. OBD II and late, late, model stuff could be different.

RACE ON!!!

 

Ok--that was sort of what I was thinking, same result--OBDI, can't extract this info unless you logged it and recorded it yourself with special tooling.

Maybe OBD II is more like a black box?

Thanks

 

Think about it, unless you turn your engine off as you coast into your parking place, the vehicle speed sensor will read ZERO from the very last time the engine was running. Pretty much the same whether you have OBD1 or OBD2.

Seriously, OBD2 is just an enhanced OBD1. OBD2 allows you to see and in some cases "adjust" or cycle components in ways that cannot be done with OBD1, but a lot of the parameters are the same.

Assume you filled up and drove until on reserve. To retain the actual vehicle speed over every second of the last driving cycle would require the vehicle to be able to retain what could possibly be hours of data. That is a lot of data that has no real world use to the car after the fact, so it has no need to be stored.

For the VSS it doesn't make sense to retain the info you are interested in inside the ECM/PCM or CCM. AS CFI-EFI has already pointed out the vehicle speed is an "on the fly" value. Vehicle speed can be constanlty changing. The ECM/PCM uses the instantaneous vehicle speed values in conjunction with other factors to adjust the Integrator value and make longer term adjustments to the BLM (Block Learn Multiple) for future use.

Some new semi-trucks do come with max/min speed recording capability. This isn't a function of OBD2, it's a "big brother" datalogging capability that uses the ability to record the OBD2 sensor values for the truck fleet owners. There are several sources for datalogging tools that will do what you want. The higher end scan tools will also save all operating parameter data to be replayed as well. Some will save the max/min value ever achieved and some will save everything. Usually the more saving capablity, the higher the cost.

Ease Diagnostics offers a "dataloging only" product and an OBD1 scan tool for laptop use that will save every OBD1 recordable parameter including vehicle speed for the entire time the vehicle is running, for review in chart or numeric modes.

 

ok, somebody is spoofing somewhere...i saw on tv (so its probably bogus right there) about the guy with the 93 camaro that was convicted of killing another motorist, based on info retrieved from his ''event recorder''....a bunch of states now have legislated who owns/ has access to ''stored'' data...

i'm concerned because at least one of my other cars supposedly has this ''feature'' and tho i've looked, i can't find any device that i can identify as such...i will disable it if i find it--there are too many variables that could enter false data and send me to jail for something i didn't do...i have been victimized by bad radar

any experts in here (reading something does not count)

 

I know I've seen this on Dateline or 20/20, but the 93-97 camaro is one of the cars that records this data for like 60 sec continuously. You can't go back more than that amount of time, but it will tell you vehicle speed, and a bunch of other inputs going that far back. I do not remember however if any corvettes had this feature.

 

All it takes to "save" the info is a memory chip of some sort. The ECM in use on all of our C4s has essentially that type of chip. That is what enables it to "learn" and make changes to the Block Learn Multiplier. The key is how much memory is available. More memory costs more money, so most vehicles do not have any more ability to store operating info than is necessary to operate the vehicle as the manufacturer intended or is legally required. Because it isn't a part of the Federal OBD2 mandate, there isn't a legal reason to have excess memory to retain past parameter info more than a few seconds at most.

It is quite possible that GM and the other manufacturers may have included additional memory capability in some models for their own reasons including in-field tests using a given product line like Camaros. There is no direct operational downside for the customer so the fact that this capability exists in the chip might not even be released to the public. An enterprising lawyer may have discovered this info and used it in a case where the last second of vehicle operation was an impact at high speed. In that not-so-normal case, I take back my comment about the speed being Zero when the engine is stopped.

If you have been told you have a vehicle with this capability, it is more that likely the mem-cal chip used in your vehicle ECM or CCM is where the info would be stored without you ever seeing it or knowing about it. The memory used in the early C4s was considerably less than that used in the last C4s which was less than was used in the C5s and C6s. In the past memory was pretty expensive. With 1Gb flash drives available for $50 now, your vehicle could easily have a mem-cal that stores your tune and the last several minutes of operating info. Most don't store this much info because even if the difference in cost is a small amount, the additional $$ per vehicle starts to add up, especially if it isn't needed or required. An additional $5 each for a memory chip larger than needed would be $150,00 for 30,000 Vettes. A $150,000 savings isn't something to sneeze at.

 

Read this

http://www.harristechnical.com/cdr.htm

Here is the list of all cars that have the "Black Box"

http://www.harristechnical.com/downloads/cdrlist.pdf

 

This is in fact my case which was why I asked--I was not asking for hours of data, I just need one second. I was doing 40mph on a 40 mph speed limit road, so if I can prove it, it would help screw the SUV driver over (ie take away any defense she might have). Her SUV rammed the cross member into the dampener on the motor, shutting the motor down at impact. Her company has already admitted full liability but I'm none to happy with their settlement offer on the property. Unfortunately when that happens, your only option is litigation, so it's time to look at building a case.

Thanks Mojo. Looks like '97 vettes up have the capability. I have the chip & the car so it's too bad I can't get the number.

 

If you have a 97, you might be able to get the HarrisTechnical people to download the info and prove your point. At a minimum, I'd download the PDF document and show to her lawyers that you have a vehicle with the appropriate capability to prove her totally at fault. If they believe you have the info, it may be just as good as actually having it.

 

from what i understand, any car with abs has a memory device that records brake use and speed. this is used by insurance companies to tell if a driver is lying about his actions in a car wreck.

where this data is stored, and if it is stored in the ecm i don't know.

i seem to remember that it is stored in an abs module somewhere--under a seat sounds familiar.

that's all i've got, but it is there somewhere. and yes big brother is watching.

 

They may be adding the ABS memory functionality to the newer cars, but I can assure you that not all ABS equipped cars have that capability. The early C4s 86-89 with ABS do not even have enough memory capability to store a code. You have to have a special Kent-Moore diagnostic tester to see the system faults when operating.

 

See the list I posted above. The Corvette isn't even listed at all.

 

Good link!! It is strange for the years shown, that others cars in the GM line had that but not a corvette.

 

My Z-3 BMW had an on board read out from the computer of your current speed. It then took this data and "Averaged" it into a stored Average miles per hour catagory. The C5 have the same thing, trying to figure out your MPG and such. Now that information is stored and visually available through the DIC.
I used the Average readout from the computer to get a COP off my back once. He claimed I was speeding and I said I wasn't flipped the DIC through it's readouts until the Average came up - he didn't know any different when I told him that this (what was on the display) was my last recorded speed before he stopped me. Of course it was an average of all the different speeds I had happened to have been doing "since" "Key-on" and engine under acceleration load. But it got him off my back

 

My 1993 has the avg MPG & the instantaneous MPG too. I just want the speed from the last 1-2 seconds.

Mojo, 1997 vette is listed so I assume C5 has it. Nice link.

 

So it is, but we all know the C5 really isn't a vette.