My last post concerned the fuel pump that was bad. On the way to the repair shop the SES (service engine soon) light flashed on and off for a few miles, then came on for good. The shop got the car running, but said that there was no codes present (SES still on). I work at a company that made the ECM for the Carprice, so I asked around. The engineers said that the SES light on with no codes indicated that the ECM was in backup mode (i.e. computer was dead). The ECM will run the car, but is in a state that has only basic function. I removed the ECM and visually inspected it for obvious damage and found nothing. I removed and reinstalled the two "chips" thinking maybe I would get lucky with a bad connection. I have ordered a Remanufactured ECM from rockauto.com ($35 plus $25 core fee), but it will not be in for a couple of days. Also, I have to reuse the two chips (EPROM and the resistor pack). I hope that the ECM is bad, and not one of the chips. Has anyone had a similar problem? I will report in a couple days if the ECM fixed the SES light.

Hasn't happened to me yet. But I have read similar reports with similar symptoms for a bad ECM.

Well, the good news is the car will still run. The bad news is that the SES light is still on? I tried the A-B shorting of the ALDL connector with the "new" ECM (old EPROM and CAL-Pack) and still cannot get the SES to flash any codes. The SES just stays on. Maybe the car has a problem with the ALDL connector or even the IGN switch, but for some reason the ECM will not flash a code. I am under the assumption from what I have read that the ECM should flash a 12 if there is nothing wrong. I even removed the ECM fuse and tried to start the car, but it would not run. That means I am atleast getting voltage to the ECM. I will keep trying, but the SES staying on is a real pain, but the car is running well.

I have maybe similar problem. No SES codes present, but SES light on AND the strangest thing is, that WinALDL software reports flow of data from computer, but can't recognise them. In any mode. Data flow is reacting on for example to RPM change, but don't show right values. I tried another car and everything is working fine - cable, WinALDL software and laptop are all right. Where might be a problem?

Padget,

Pull any jumper you might have inserted from the ALDL. Turn the ignition off for at least 20 seconds. Carefully observe the SES lamp while turning the ignition to RUN (not START). You should see the lamp illuminate for about 1/4 second, go off for about 1/4 second, then turn back on and remain on. Does this occur?

I'm a little disappointed that some of the engineers at the "company that made the ECM for the Carprice" could not remember that.

Nope, the SES light was on and stayed on (no jumpers on the ALDL). It never blinked? The IGN switch seams to have a detent for accessory, but does not power anything. The when I continue to rotate through to the next dentent the SES is on (this is the postion the IGN is in after a start).
Note: I have a 12 pin ALDL, but only the top row have pins installed.

Are you sure the wiring for the SES bulb isn't shorted/grounded?

My SES light comes on with no codes when my gas cap is not on securly with at least 3 clicks. I`ve solved other peoples simular problems that way. One was told she needed a new computer.

The IGN switch seams to have a detent for accessory, but does not power anything. The when I continue to rotate through to the next dentent the SES is on (this is the postion the IGN is in after a start).

Yes, that would be the RUN position (see above).

Corning - Of course the SES is grounded. It wouldn't be on if it weren't grounded. (I know what you mean, though.) If the wire for grounding the SES is inadvertently grounded outside the ECM, it may be a problem. You can test that right at the ALDL (Pin D) with the ignition off:

http://72.19.213.157/files/ALDL.gif

If that checks out, and the SES doesn't "bounce" when the ignition is first powered up, you have a firmware or PROM prolem, likely a checksum error. Try a different PROM/CALPAK.

ALL: Thanks for the replies. I have checked the ALDL and have the following to report. IGN in lock: A= 38.5 ohms to Ground. D = 7.6 ohms to Ground. IGN in RUN: B = 4.98 Volts DC. I also bought a Haynes Repair Manual and have been reading up on things. The manual says to have the ignition Key On and then to short the AB pins. I tried it this way and still got the constant SES light (no blink on IGN and to codes flash). I now have the Chassis electrical system print to reference, but the ECM just goes to the SES and the ALDL. Maybe the 7.6 ohms is normal, so that the SES blinks on IGN for ¼ second. Then, it would normally go out if things were correct. I will ohm the wires out Monday 10 July to the ECM, and if things checkout I will order the EPROM as suggested by Blue Bowtie.

ALL: Thanks for the replies. I have checked the ALDL and have the following to report. IGN in lock: A= 38.5 ohms to Ground. D = 7.6 ohms to Ground. IGN in RUN: B = 4.98 Volts DC. I also bought a Haynes Repair Manual and have been reading up on things. The manual says to have the ignition Key On and then to short the AB pins. I tried it this way and still got the constant SES light (no blink on IGN and to codes flash). I now have the Chassis electrical system print to reference, but the ECM just goes to the SES and the ALDL. Maybe the 7.6 ohms is normal, so that the SES blinks on IGN for ¼ second. Then, it would normally go out if things were correct. I will ohm the wires out Monday 10 July to the ECM, and if things checkout I will order the EPROM as suggested by Blue Bowtie.


Do NOT further check the ECM or related wiring for resistance with a volt-ohm meter. As with any delicate and sensitive electronic equipment, running an ohmmeter against the computer circuits can cause them to fail (you're running a voltage through the circuit that's incidental to the ohmmeter functioning). You could be putting a voltage across a circuit that's not designed to have that much voltage or current in it.

Check for the presence of a voltage as above in Blue Bowtie's diagram. This is safe, running voltage from an ohmmeter is not.

Good point from Silicon. You shouldn't indiscriminately start checking ECM connections with an ohmmeter. There are some which are safe, some which are not.

The fact that you have read almost 40 ohms from ALDL terminal A to a good ground indicates a problem. There should be no more than an ohm or less, ideally zero. I'd start by verifying the ECM grounding. It is safe to measure the ECM case resistance to a good chassis ground. If there is more than 1 ohm, start checking ground connections in the wire harness and at the engine.

Forget about ordering a MEMCAL/CALPAK for now, since the circuit did not check out properly.

Thanks for the information and concern with the multi-meter issue. I will use caution, and generally accepted trouble shooting methods while investigating the SES light. I have been on vacation to Florida visiting family, so now that I am back the diagnosis can continue.

Four hours later:
Status update 12 July 2006: The ALDL pin A (GND) to the metal of the ECM measures .2 ohms. The ALDL pin A, and the metal of the ECM, to the chassis of the car (i.e. the fender ground lug by the battery) measures 26 ohms. This was measuring 38.6 ohms before I cleaned all of the connections. I have cleaned the fender ground lug, the engine cable ground from the battery, ohm checked the battery ground cable, and cleaned and ohm checked the ECM grounds that come out of the cable bundle on top of the engine block. Everything checks out good. I even removed the ground cable from the engine lug, disconnected it from the battery, and disconnected it from the fender lug (i.e. the negative cable was removed from the car). Then, I measured .2 ohms between the engine lug and the fender lug? I then reinstalled the ground cable fully expecting .2 ohms, but instead it measured 12 ohms? I do not understand the 26 ohms between the ECM metal case and the chassis ground lug, or the 12 ohms measured between engine ground and fender ground? Anyway, I guess the good news is that the ALDL pin A to the case of the ECM measures .2 ohms. I assume that this means I have a bad EPROM, since I still have a constant SES light with no blinking on ignition. I know it is not the correct thing to do (shot gunning parts), but I went ahead and ordered an EPROM from rockauto.com. If the EPROM does not fix the SES, then I know the EPROM is not the troubleJ.

You need to get a good ground to the ECM. Disconnect the battery ground cable, then unplug and reconnect the ECM harness connectors several times. The pull/reseating of the connectors can help wipe the contacts clean and establish better connections. The ECM mainboard should be internally grounded (via the mounting screws) to the ECM case.

You might also want to remove the access cover and unseat/reseat the CALPAK or PROM a couple times to achieve the same connection cleaning.

Caprice Group,
Thanks for all of the replies and advice. To make a long story short, the problem with the SES light was a short to ground around the steering column. The D pin on the ALDL measured 2 ohms to chassis ground. After I moved the wiring bundles around the problem went away. The replacement ECM was causing the car to run sluggish because when I installed the original ECM it runs like a champ! It has 120,000 miles on it and I am looking forward to many more road miles.

I was going to suggest something similiar. I have an 86 4.3L that wouldnt get power to the computer properly. There was a fuse under the hood that came loose from the connector and was bouncing all over the body. Replaced the fuse and holder. Good to go.