“Pre-OBD” Diagnostics

[Patrick O’Connor]

Hi everyone,

I drive a 1991 Camaro with the 3.1L V6. It has the old ALDL diagnostic connector. I know that I can jump across two certain terminals to get trouble codes (12 = no distributor reference pulse, 13 = oxygen sensor, etc), but is this system capable of giving more information than that? More modern systems can give things like stored codes, long term fuel trim and other fancy stuff like that, does a system as old as mine have that capability if connected to a “proper” scanning tool?

Thanks,
PatrickO

Topic

[dave]

Prior to 1995, OBD1 was a proprietary design; each manufacturer could come up with their own codes for whatever they wanted. Since 1996, OBD2 has generally been standardized among all automotive manufacturers.

So, in short, who knows what you got or what information you get. Pulling OBD1 codes can be quite a mysterious procedure.

[John B Kobberstad]

A Snap On MT2500 has the capability. There are 3 different adapters for GM vehicles. One is for GM ABS and my guess would be the other 2 are for engine and body computer connection I’ve never had the opportunity to use mine on a GM vehicle as I only have Chrysler vehicles. My son used it on a 95 Camaro though but it was kinda strange as his 95 Camaro had an OBDII plug in it. But it is possible to retrieve OBD data with the MT2500. It all depends on what data GM made available in it’s control modules for that year. Email or text me a land line number and a good time to call. Contact info is in my signature below.

[college man]

I don’t think you will get much sensor data.
Most were just diagnostic codes.

[Its me]

Back in the day I used an ALLTEST 3256… You can get them dirt cheap nowadays… Tells you much more than you might think… I used mine predominately for GM’s made in the late 80’s… I still have it somewhere!

Link to scanner on Ebay

[Patrick O’Connor]

[quote=”ToyotaKarl” post=54161]Back in the day I used an ALLTEST 3256… You can get them dirt cheap nowadays… Tells you much more than you might think… I used mine predominately for GM’s made in the late 80’s… I still have it somewhere!

Can you give me an idea of what sort of info I might expect?

[Patrick O’Connor]

ToyotaKarl,

I asked the ebay seller a similar question, and he responded,

“It will reveal stored codes as I understand it and tell you sensor values”

I also called the number that appeared on the front of the manual in the picture. I actually did reach someone at “Automotive Test Systems, Inc.” but they have no information for this older unit.

At least being able to read some of the sensor outputs could help with diagnosis.

[Its me]

OK I pulled out another old one I had, this was a 3250, but is pretty much the same thing.

Here is what it can tell you:

A/C Switch
Air Control
Air Flow
Air switch
Battery Voltage
Baro
Block learn
Booste wast
CCP Solenoid
Clear flood
coolant temp
Coolant fan

Crank
Cross count
Dwelll + RPM
EFE Solenoid
EGR %
EGR Pressure (V)
EGR Solenoid
EPR
EST
Exhaust Gas
Freon/Head
Gear 3/4

IAC
Igniyion
INJ Base PW
integrator
knock rtd
loop status
LV8
Man air temp
MAP/VAC (V)
MPH + TPS (V))
Nose switch
Oxygen (V)

Park/Neutral
Power Steer
Prom ID
Rear VAC BRK
Selection
SPK ADV RTD
Spark Count
TCC SOL + MPH
TPS (V) + RPM
Trouble Cd
Water INJ
WOT

When I used this, I used the Baro quite a bit as well as LOOP STATUS to check if the car was in OPEN or CLOSED Loop. Also you could check the O2 readings and see them switch back from lean and rich. Also used the TPS function A lot. Those computer controlled carbs had to be set just right…(anyone else remember this fun of drilling in the protective cover on the carb)

[Patrick O’Connor]

Wow, that’s a LOT of stuff! Especially considering the age of the car. OK, I’m convinced that it would be worth it to pick one up. I have a few different issued this could help me track town.

I guess we can’t make a blanket statement about what’s available informationwise for pre-OBD-II cars, but we do know that this particular car (and possibly most GM vehicles of this time) can tell you a lot through their ALDL connectors.

If anyone has a different conclusion or experience please let me know.

-PatrickO

[Patrick O’Connor]

OK, I bought the scanner, hooked it up to my car, but it won’t read any codes! Display lights up and goes through setup (cycles thru the numbers 82 to 86 for year selection), but then gives a blank display (four dashes) indicating either no data or wrong data type. Will this tool only work on 81 to 86 cars? (checked fuse in unit, fuse is good)

[Author]

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