First off, the car is a 92 305 TBI and I have a GM code reader and its owner’s manual that says what each code means. Starting yesterday my engine light came on, so I stuck the code reader in and it flashes a total of 7 times but stuttered on the 5th flash and stayed on while in “run.” No repeating codes at all. Without the code reader it flashes 7 times like I understand is normal but stays on while the engine is running like there is a code. Yesterday morning had this same glitchy code, but leaving work yesterday did not have any code. I plugged the reader in and only got code 12 like it should and it flashed 7 times while running and stayed off. This morning had this glitchy code again. The engine has been running flawlessly with and without the glitchy code.
This exact same thing happened a couple months ago where the engine light would come on mostly while cold and went off while warm at highway speeds until my distributor rotor finally went out, but it also gave me what looked like codes 52 or 53. 52 being either an ECM problem or system voltage too high, and 53 being system voltage to ECM too high, alternator voltage not normal or VATS fault. I doubt those codes are relevant but I thought I’d mention it. I replaced the distributor rotor and the cap and all engine codes disappeared and it no longer flashed 7 times while starting the car. The only code it had while off was 12, which is normal. But now that problem has come back and the car runs better than it ever has.
The owner’s manual for the code reader doesn’t mention anything like this, and I haven’t seen any other posts about this. Any blatantly obvious ideas that I’m missing?
Here’s an unlisted YouTube video of the code

 

Everything has acted the same until this morning. Before I started up to go to work, it had code 12 like normal so I started and it didn’t have a code. I idled for a little while and a code showed up after 30 seconds or so. Still the weird one. I left anyway and during the 20 minute drive at highway speeds, it came on for a few minutes at a time. Not blinking but just staying on for a few minutes, then go off for a few until about halfway through when it stayed off entirely. I slowed down once I got into town and it came back on, and stayed on. As I was pulling into work, it was flashing irregularly almost like it was trying to give me some codes, but it wasn’t intelligible. I think I might’ve gotten “21” out of it, but it felt more like it was coming on every time I hit the smallest bump. Yeah, I know that flashing while driving is very bad. The car ran perfectly the entire way and I’m idling as I’m typing this with no issues. Tested the code again, and of course it’s still the same one.
I was afraid of this being a warning sign for some serious expensive issue, but I’m thinking there’s just a problem with the diagnostic program, or whatever it may actually be called.

 

Disconnect battery ground for a minute or so and ditch the code reader. Short pins A/B of ALDL connector and determine that code 12 is reported with key on-engine off. Remove shorting pin and drive until code(s) seem to reappear. Stop and repeat above to get blink-out codes.

 

It’s been a little while, but I’m still having the same issue. For a while, i was thinking it was something to do with my transmission (700r4), since I’ve had issues the whole time that I’ve had the car. Got it completely rebuilt from a local shop that is supposedly the best around, and it was there for over a month before I got it back. When I picked it up, they said that in the A wire in the 4-pin connector that goes to the transmission, which goes to the converter lockup, didn’t have any voltage and they had no idea why. Turns out that the TCC connector was broken, unplugged from brake switch, and tucked above all of the other wires under the dash. I replaced the connector, plugged it in and transmission is working great now. That weird code is still here.
I’ve disconnected the ground cable and removed the ECM fuse more times than i can count and this code will not go away. The thing is overwriting all other engine codes that could potentially appear, and this is my only vehicle, so I’d like to know when something is actually wrong. I’m completely lost on what is going on.
There are a few things that I know aren’t working the way they should, and will be fixed later on, but I haven’t gotten there yet. Maybe that’s causing something?
1. The car had a combustion leak when I got it, so I pulled the heads, had them rebuilt, and put them back on. While putting the engine back together, we cut the aluminum emissions tubes off of the exhaust manifold. Just barely got them out with the tubes, and certainly couldn’t fit them back in without moving the block. We’ve just left the smog pump unplugged, but the EGR still routed in. The car didn’t seem the run correctly without it. I’ve always felt like there would be some negative side effect of doing this.
2. On the way over to the shop, I noticed that my voltmeter was going crazy while I idled at a stop light. I have dual 4K cfm fans that use more power than my factory 105 amp alternator can give out, so I’ve been wanting to replace that for a while.
3. My oil gauge reads low. At cold startup it stays around 30-45 psi or so (even while driving), and idles hot at around 4 psi or so. That’s with 10W-30 synthetic blend oil. The car runs very well, so we’re thinking the gauge just isn’t accurate. I haven’t hooked up a mechanical gauge yet.
4. A few people have mentioned how the car runs a little rich. I haven’t replaced the O2 sensor, but I imagine it’s not a bad idea. It’ll be the next thing I do.
5. Heater in the car doesn’t work well. I’ve pulled the dash and checked on the heater core, and it looks brand new like the previous owner said, but I’m thinking there’s a blockage that I plan on pumping out before it gets too cold. I’m not suffering through winter again.
6. My speedometer is not working, and stopped reading anything, without warning, around the time that my distributor rotor went out, in July. It’s got the wrong gear/ratio combination, so it was not accurate when it was working. It also gets weird signal pulses from time to time. Before it went out, it would occasionally drop to 0 and come right back up, and on one or two occasions, it jumped up to around 80mph at 60 actual, reading around 49. Since it’s gone out, it stays energized but very rarely gets a little bit of of something for a split second. When I got the car back from the shop, I turned the key to run and it went absolutely nuts but quit maybe 5 minutes later. The radio was in demo mode, so the shop must’ve disconnected the battery at least for a little while, and the MAP sensor also got knocked loose at that time. Not sure if either of those correlate. Haven’t seen any movement since.
Based on all of that, could any of those cause this strange code?

 

This is starting to become a problem.
First off, my registration goes out next month and I don’t think I can renew it with an engine light on. The engine isn’t acting right anymore, I know something is wrong, but I can’t see what code it’s trying to give me.
The engine usually idles around 1000 RPM once it’s warm and stays like that, but a few months ago, it started dipping closer to 800 and you can feel that something isn’t quite right. Maybe a month ago, I noticed that the black plastic vacuum line that connects to the elbow on my MAP sensor was extremely loose, so I put some electrical tape around the end and shoved it in. It holds very tight, and significantly improved my idle. I went through a car wash a little while ago and it would idle lower and lower until it hit 500-600, suddenly surge to 1500, then steadily drop down lower and repeat. I turned it off, then on the drive home it was surging by about 500 or so RPM at a steady 35 MPH. My first thought is that it’s misfiring, but it does great at higher speeds and RPMs. I am still learning how to work on cars, I know these are signs of something, but I have no idea what they mean.
I’ve got a replacement oxygen sensor, so I was messing with it while changing my oil a couple weeks ago. The one on the car is completely rusted to the manifold, and wouldn’t budge even when the engine is hot or with every rust-breaking lubricant that we sprayed on it. We used one of those sockets designed to take them out with the wire intact, and it just kept skipping. Decided that it might’ve been for the best to not cut the wire and pull it out with a normal socket until we know it’s an actual issue, and I’m betting it is now. That’s my only other guess now as to why my engine code is screwy.

If you know anything, please let me know. I can find out why engine codes are going off, but without them I have no idea what I’m doing.

 

If the ECU won't reliably give you codes then it may be faulty. Swap in another ECU and see if it will give you codes. Either that or get an ALDL cable and go into live data and see what the code flags are, etc. If you can't connect to the ECU then you need to follow the troublshooting for communications problems and it's absolutely possible that the ECU has a cracked circuit board, etc and may need to be replaced.

GD

 

The ALDL cable + software were around the same price as an ECM, so I talked to some people that know way more about cars than I do, and they suggested I go with the computer just in case the data proved it was bad anyway. Had to wait until I could actually afford it, and finally tried it. I had to reuse my original PROM.
Just drove it around 35 or so miles and it seems like almost everything was improved. The car responds quicker, doesn’t surge through a range of RPM on gas or idle, uses just a little less RPM in general, shifts a little nicer, and actually has an oil level when warm (peak of 16psi while driving 70 at 2200-2500RPM) But the code is still the same and doesn’t do anything else.
I did notice that, while I was idling in gear, one of my fans kicked on and my volt gauge dropped to 9-10 for a few seconds, then jumped back up to the 13-15 range, like it’s usually at. Might have to look into that.
I’ve got a small trans fluid leak (that I’ve been on top of) that should be easy to fix, so I plan on doing that later this weekend. Might be able to finally use that throttle body rebuild kit that I have, clean out the IAC valve (since neither have been done yet), and see if I can find the right socket to remove the O2 sensor. Other than that, I guess I’ll have to get an ALDL cable when I can.

 

Turns out the trans fluid leak was much worse than I thought. Had to pull the radiator and rethread the port for the trans cooling return line, which took all day. Once everything was corrected and back together, I had the car idling for well over an hour while I checked the fluid and whatnot and it was the closest to perfect that it’s been so far. I’ve still got the useless code.

Update: I also pulled and cleaned the IAC valve and the port inside of the TB with carb cleaner. It didn’t feel like it was even tightened all the way when I took it off, but it improved my idle significantly (go figure) and a little bit of the reaction time, but that didn’t change anything with the weird code.
I’m starting to wonder if the problem is electrical, like two wires getting a little too close and bouncing each other’s current to the other. Once my tax refund comes in, I plan on finally getting a new alternator, an ALDL cable, and I’ve also been wanting to replace my semi-faulty headlight switch and check on the wiring to my VSS buffer, and both of those last things are easier to do if I pull the dash. I’ve already had to pull it once, I don’t necessarily want to do it again, but I wonder if bypassing the harness by attaching a separate new wire on the ALDL diagnostic wiring to and from the ECM and the SES light using those little plastic cross connection clips would yield any results. It’s just an idea, I haven’t even looked at any diagrams yet. I’ll look into it more before I decide for sure.

 

Hopefully final update. I still think the issue is electrical at this point, and haven’t done anything yet. The car has been functioning fine, and I arrived at a restaurant early to meet my roommate and idled for a little bit, and the engine code turned off. I shut the car off immediately and tested the code and got the diagnostic code and code 23. Finally! According to my code reader book, it could be a few different issues, but at least I know where to start now.

I had been suspecting the TPS to be going out, and it looks like I might be right. I’m still going to look into the electrical issue at some point. Thanks anyone who might have seen this.

 

Look up the code in a 90-92 Camaro service manual. Follow the diagnostic charts in the book. It might lead you on a bit of a chase, but if you follow the steps in the book, it'll step you thru eliminating possibilities until the problem is solved.