Just a little history first. I have a '95 LT1 Z28 with some addon parts. I use a hypertech programmer, had to have some dealer work done on the car so I removed programming, then of course reprogrammed car when they finished the work. Everything worked fine, couple months later transmission pooped out. Bought new trans and converter installed them, everything ran like a top! 6 to 8 months later SES ( Service engine soon) light comes on! When SES light is on the fans kick on, this happens even on a cold start. When driving the SES light is off, but stop at a light SES back on with fans!. Hookup programmer it says can not find VIN code!. Took it to a shop to hook it up to computer, their computer can not read pcm! The car runs fine and has all kinds of power except for the problems above. PCM bad or just needs to be reset in some way? Also can it be taken out and sent off to be reprogrammed or do I need to buy a new one? Any help you can give me will be great. Thanks in advance

 

The shop probably saw the 95's 16-pin OBD-II style ALDL connector, and hooked up an OBD-II scanner, which can't read the 95's OBD-I PCM. Try a shop with an OBD-I scanner, and a 12-pin to 16-pin adapter plug, or use jumper wires as Shoebox shows:

http://shbox.com/1/xraycable.jpg

Alternatively, there is software available that you can use with a new cable:

TTS Power Systems

It's common for the PCM to turn the fans on full time for some trouble codes. The most common is a blown fuse for the AIR pump causing DTC 29. There are other codes that will turn on the codes.

 

It can run that good, on top of the fans kicking on when the SES light is on the computer retards the timing also. I had the same issue with a local shop, ended up going to the dealer.

 

It's common for the PCM to turn the fans on full time for some trouble codes. The most common is a blown fuse for the AIR pump causing DTC 29. There are other codes that will turn on the codes.[/QUOTE]

Well mine with kick the SES and turn the fans on at cold startup. Then if I drive it the SES goes off and the fans stop until get to the next stop light.

 

Wow I got the same problem with both fans. They come on early when cold. The air injection has already been deleted so i never checked the fuse. Would the retarded timing cause pinging or predetonation?

 

Check the AIR fuse. Even if the pump is unplugged you will get DTC 29 if the fuse is missing or bad. The AIR pump only runs on startup for a couple of minutes so that's when the code would set/fans would run. Or scan it and find out what the code is rather than guessing. Retarding the timing would reduce knock (detonation).

 

The fuse was blown for AIR injection. I replaced it but sadly the fans still come on. The SES still comes on and off as before. I didn't have any other trouble codes either. I hope we can figure this out because the fans coming on early causes warm up time to be longer. The fans are loud too as if they have been coming on early for a long time causing them to wear out a bit.

 

It sounds like you have a software problem. If the PCM is turning on the SES light there are still codes.

 

Pull the "PCM BAT" fuse for 30 seconds to clear the stored codes. What code reader did you use and how did you connect it to the 16-pin ALDL connector?

 

I will try that in the morning instead of disconnecting the battery. The code reader used was a snapon(large) will full capabilities recently updated software in it. It used the key type inline with the wire. I guess there are several different keys possible, probably other manufacturers with similar translation setup ie ODB1-ODB2. The only code read was the AIR injection. I though it was because it was deleted so ignored it. But the fuse was probably the cause. Now I replace the fuse though and still get SES turning on and off. Usually off at idle but not always, and then when accelerating it turns right on. It sometimes will go out during driving. Really weird, but tends to be off when at idle, and on when driving. Generally.

 

Let us know if/when you fix your problem. I had the smae exact problem with my computer. I still cant read it. My SES light was coming on in the same way yours is. Turns out my prob was the AIR fuse. My SES is out now, but I still cant connect to the PCM with any type of scanner, except for my hypertech. I can program no problem with it. I have checked the serial data line for continuity and it tests out good from the ALDL connector to the computer, from connector to EBCM, and from connector to Air bag module. I replaced my computer at that point thinking that it must be a bad connection in the comp itself. But still cant read the comp, so Im stuck with living with it for now. Luckily Im not having any issues I need to worry about. But it would still be nice if I could scan the comp.

And I have not tried hooking up to it with a laptop yet, cuz I dont have anyone in my area that could help me out on that front.

So if you get this prob fixed, I would love to know what you did, so I could try it.

 

Yes I will post the results. I just got home and about to try resetting the fuse and a few other things. I feared that the fuse blown was a 25, and the circuit is only 20. I cannot be sure how many times the previous owner blew out a larger size fuse. I was thinking it may have caused damage beyond but I'm just speculating.
I think you gotta jump wires to get a scanner to work. Not sure if you knew that already. Never done it myself since the snapon had the key inline with the cable.

Hey does anybody know if jumping A-B on the ODB1(95) port will allow me to read the code as it blinks? Thats how I remember doing it before. That way I should see the code 12 three times to confirm the computer seems to be okay.

 

That only works on a 93. 94+ requires a scanner (or a PC with an interface cable).

 

We covered that in post #2.

 

ya the scanner with jumpers was in response to Zfbod94. It didn't appear that he knew already.

I still have an SES coming on but now appeared to stay on since removing the PCM BAT fuse. Autozone could not read a code. Sound like bad news thats not supposed to happen.