Have you checked to be sure the ECM has constant battery power?

Also, The Fiero Store sells ALDL Tools. One is very comprehensive. The GUI is free to use from download but you need to buy the $84 adapter to monitor/record data. The guy who developed it name escapes me at the moment [smile]. I now make what I am calling the GM ALDL "Paperclip" Adapter. It's a lot better than jamming a paperclip in the ALDL connector. It can put the Fiero in NORM, DMFACT, or DMDIAG Mode... all at the flip of a switch. It has a Instruction/Error Code placard and a Trox screwdriver teathered to it.
I am selling it for cost plus shipping. It's a nice thing to keep in your glove box.

GM ALDL "Paperclip" Adapter

I am also available for free consultations via email or phone... but nothing beats this forum.

Is this your first Fiero? If so, welcome to the family. The folks here have a lot of great advice. I chip in when I can. My expertise is talking to the ECM via the ALDL. I am designing a bench top ECM tester. It will simulate the entire Fiero around the ECM. It's a background project but coming along.

Buying an ECM is ok, even if your current one turns out to be ok, having a spare is not a bad thing as long as you don't pay too much for one.

Make sure you get the ECM model for your exact Fiero model. Different years and engines use specific ECM models, and then the PROM must also match your Fiero model year, engine sise, tire sizes, federal or California emissions, and which manual or automatic transmission model is installed. If you get the right ECM with the wrong PROM, it may work, but not properly.

My free GUI that you can download has a chart in the Help the gives you a bit more detail on this.

[This message has been edited by Romsk (edited 04-20-2025).]

One final thought. You might not want to just swap out your ECM if there is something wrong in the wiring/system. You may damage your new one the instant you install it.

I have studied the 2.8L ECM schematics. I am an electrical engineer so I can say the SES signal driver circuit in the ECM is fairly robust. The best thing to do is to totally isolate the SES wire from the rest of the car at the ECM. There are pin removal tools to do that, but finding the right one is difficult. If you are good at soldering: One trick is to cut the SES wire about 6 inches from the ECM and use an incandescent Test Lamp with 12V on the clip and the tip on the wire from the SES. The diagrams for the other ECMs have similar circuits and may even use the same wire colors. We can tell you which wire to cut if you want to try that.

Now, if the SES circuit is isolated from the car:
Short pins A and B on the ALDL Connector (we can show you how)
Ignition Off: Test Lamp Off
Ignition On Engine Not Running: The Test Lamp should blink Error Codes (EC). EC 12 (which means no error in DMDIAG Mode) is blinked first 3 times, followed by each EC stored 3 times, then back to EC 12. If you get more than 3 EC 12's in a row, then no Error Codes are stored.

If the Test Lamp does not blink or if it does anything different, then the ECM "may" be malfunctioning. If the ECM does work properly in this test, leave the ECM isolated and hunt down the problem from there to the SES lamp. Remember, 12V is on the other side of the SES lamp, so you will read 12V through the Lamp with a DMM at the cut wire end that is not connected to the ECM.

Once you resolved the problem, wear safety goggles and have a safety observer present. Slip heat shrink tubing over the cut SES wire, solder the wires together, and shrink the tubing with a Bic lighter to cover the splice. Keep a fire extinguisher on hand. Or add a small connector there at the cut wires instead - for future troubleshooting.

[This message has been edited by Romsk (edited 04-20-2025).]