94 Corsica blues

[turboanth]

Okay Ive got a 94 corsica with the 3100 engine. Its had an intermittent check engine light, and high idle since I bought it. Its got 143K miles. The alternator, batt, radiator and a full tuneup have been done. I went to try and pull the code(s) with the paperclip method and I cannot get the light to do anything but stay on. I took the lower dash off and traced the wires, but I found nothing all the way to the main harness. Any ideas? I have never had this problem with a gm before. Thanks

[bszopi]

Paperclip method was eliminated in 94. Need to use an actual scanner to pull codes.

[turboanth]

So can I take it to an Autozone or something to get the code pulled?

[robertisaar]

possibly, but if you know someone with a laptop and an ALDL cable, you can scan them yourself...

[asylummotorsports]

'94-'95 L bodies are OBD 1.5 when GM couldn't decide just what the hell it wanted or was mandated to do.

Can't be tuned, is hard to diagnose and really impossible to deal with.

AutoZone should be able to pull a code. Just go from there

Good luck with it.

[robertisaar]

'94-'95 L bodies are OBD 1.5 when GM couldn't decide just what the hell it wanted or was mandated to do.

Can't be tuned, is hard to diagnose and really impossible to deal with.

AutoZone should be able to pull a code. Just go from there

Good luck with it.

in the present situation, yes all of that is true.

if you want to split hairs(and we all know i love to), 1.5, as we know it, is actually OBD2, with OBD1 signaling protocalls.

it's tuneable and has the same diagnosis capability as OBD2, but no one wants to hack through it for tuning. diagnosis on the other hand, was fixed a while ago.

[tkoforpresident]

yeah diagnosis is no biggy. my actron scanner 9150 reads it no problem. also, it's sad to think that if someone wanted to take the time to "hack" this pcm then we could be flash tuning like the obd2 big boys.....

[turboanth]

So if I buy the cable and the proper software, I can use my laptop as a diagnostic tool? read realtime data etc?

[robertisaar]

if you're good with electronics, you can build your own cable pretty cheaply compared to the $60 it normally costs for an ALDL cable... isaachayes is definitely running his own, last i knew.

software is free (tunerpro RT).

[IsaacHayes]

Yeah there is a definition (several I have tweaked/made) that runs in TunerPro and you can read history codes, current codes, clear them, read sensor data etc. Sensor data is good stuff, when I swapped on my 65mm TB, I had a high idle. Fired up the laptop and saw the TPS was reading 4% when the throttle was closed. Swapped the TPS from my original TB and all was good again. Glad I looked at the laptop instead of thinking it was a vacuum leak and chasing my tail...

You can build a simple 2 transistor cable, or a surefire one. I did the later, and added an activity LED to the schematic with an extra transistor and resistor. It actually comes in handy other than looking pretty as you can seen when the disable coms command went through and tell when it's in communication mode with the laptop over the normal chatter that is always there. I also used the small package voltage regulator that looks like a standard small transistor as it was more compact and could handle the power just fine.



I bought the parts at jameco.com, other than the resistors and diodes, I had those. I bought the project box and PCB from radiosnatch. I built two, sold one. The chip I used was a Texas Instruments MAX232 that was only 50 cents each.





I used speaker wire for the 2 wires that go to the ALDL and tinned the ends, and used a Cat5e short patch cord (was like $2) for the cable that goes to the DB9 serial connector. Got those parts from jameco.com too.



Oh, the Blue LED is on when it's powered on, so you know to turn it off to save the 9v when not in use. The other LED I used for the activity was a yellow high brightness. I later took a scotch brite pad to the LEDs to make them matt so they were more omnidirectional and weren't so blinding. I also had to increase the resistor values to bring the brightness down as high brightness LEDs today are too bright for indicators, but I wanted to see them in sunlight too so I left them fairly bright.

This folder has my definition files for tunerpro and scannerpro. They may be a little dated from what I have now, but work just fine for what you need to do.

http://isaachayes.60degreev6.com/aldlcable/

[3400-95-Modified]

Autozone and advance does not (in my area at least) Carry the proper equipment to scan a OBDI or OBDI.5 unit they only know how to do OBDII.

[IsaacHayes]

Yup, only tool I've had work on my car was an EXPENSIVE snap on unit that could do it. So I made my ALDL cable and it's even better than a scan tool with all the data I can see.

[Scott_68B]

This folder has my definition files for tunerpro and scannerpro. They may be a little dated from what I have now, but work just fine for what you need to do.

Interesting. What source of information did you use to create your definition files? Looks like the same basic interface circuit I use for OBD1...neat that it works for 1.5 too.

[IsaacHayes]

there is info for it all in the ALDLstuff.zip on moates.net files for the PCM, I used that and modified the def that was on tunerpro.net's site, corrected a few things and added etc.

[Scott_68B]

I didn't realize that zip file contained info for OBD1.5 too. That really helped I'm sure. Thanks for the info.

-- Scott