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Old 09-16-2002, 07:01 PM   #1
wolfman
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Default Fellow techs please confirm diagnosis

I am working on a 91' SL1 manual. With the help of a donor car and some new brake pieces the car is nearly road ready. EVERYTHING now works with 1 exception...the SES light. The bulb is just fine as are all the electrical connections. The car starts, runs, and drives just fine. Cooling fan and all other lights/guages are functional and normal. When I jump the diagnostic port the SES light does NOT flash, BUT the "hot" light comes on as well as the radiator cooling fan. I am thinking BAD PCM? Do not recall seeing this before nor do I remember anything helpful from my days at Saturn. So what do you guys think? Am I right (Bad PCM)?
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Old 09-17-2002, 01:24 PM   #2
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Wolfman,
No one has responded so I will give it a try.

Can you swap the PCM from the "donor car" to see if the problem follows?

Are you sure that no one has messed with the dash wireing?
Are you sure no one has messed with the cooling fan wireing?

I assume the ses light will light when the engine is started (bulb check).

Do the operating voltages of the electrical system seem alright?
Is there any ac riding on the DC?
(voltage regulator/rectifier)

Being that it's a 91'
It could be a corrosion/dirt problem

It could be that the SES light is just a symptom of a entirely different problem.
(like brake lights messing with cruise control).


Good Luck
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Old 09-17-2002, 08:20 PM   #3
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Default more info

If ONLY it were that easy. The donor car is a wrecked 92' SL2 automatic. From which the complete interior and mouse belts along with various mechanical bits transferred into the 91' SL1 manual. Swapping out the PCM for the 91' SL1 manual is NOT an option. The SES light's bulb is fine..confirmed with BOTH a continuity tester and by swapping it for the oil light where it worked just fine. A test of the PCM's output wire at the PCM's conector revealed NO signal voltage with the key "on" engine "off". I believe the car is simply running in closed loop mode all the time although it is doing a very good job of it. Wiring shows nothing unusual or any evidence of tampering of any kind. WOW I guess I have eveyone stumped with this one! Time to go PCM shopping I guess.
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Old 09-17-2002, 08:49 PM   #4
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WELL IT SOUNDS TO ME LIKE IT MAY BE...... BROKEN

I HAVEN'T A CLUE WHAT'S WRONG BUT WILL BE VERY SURPRISED IF IT'S THE PCM!!! YOU RARELY HEAR OF THE PCM FAILING.

BLACKBIRD
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Old 09-17-2002, 08:59 PM   #5
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Does the SES light come on on the key on self test with the rest of the dash lights? I have never seen this before myself so you may just be down to making sure that all the wiring is intact, no opens, grounds or shorts. Make sure that the terminals are not backed out anywhere. I say this because last week I had a car in for the major service and could not reprogram it because as I found out the wire from/to the PCM and data link connector was backed out at the PCM connector. Back in place and the TECH II was now talking to the PCM.
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Old 09-17-2002, 09:14 PM   #6
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Ssicarman,
That's just it. It does NOT light up prestart (self check) I can run voltage to the disconnected IP cluster and make the light come on. I have removed the PCM and checked the pins/connector sockets and that all the wires are where they are supposed to be. Again, I can not get the PCM to send signal voltage out of the SES light port NO matter what I try. And then there's the whole weird hot light fan thing described in my first post. I'm thinking the quad driver portion or perhaps the RAM memory portion of the PCM is dead...the car starts and runs/drives just fine so if a bargain basement PCM is not to be had I may just let it slide awhile.
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Old 09-17-2002, 09:34 PM   #7
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The PCM grounds the SES light to turn it on.
Power is supplied through the IGN1 fuse in the UHJB.
It enters the cluster through term B of the cluster conn. IGN! fuse supplies power to the brake TT lap belt TT and coolant TT as well.
The ground side of the SES light goes out term C of the cluster.
The PCM grounds the SES light wire(brown/white) at term J2A01- which should be the brown 12 pin conn. According to the book if you can ground this wire and turn on the light you have a bad PCM
Hope this helps, sorry it took so long

EW
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Old 09-17-2002, 09:34 PM   #8
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Have you tried cracking the PCM open to check for burnt circuits? I think though that like you I would just leave it for now and see if you can happen on a cheap PCM. Maybe see what Joey can do for you. You could very well be right on the quad driver.
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Old 09-17-2002, 10:10 PM   #9
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ssicarman and sattech,
Thanks for helping to preserve my sanity. I have already run the ground wire to the brown/white wire from the PCM and viola! The SES light comes on. So I guess the PCM is the culprit. I have no desire to crack it open and risk doing additional damage as the car does start/drive/run now and the while State inspection standards for my county in Maine do require it to work, most inspection stations "forget" to check...in any event I have until November to fix it. I am thinking that either the car is running in closed loop all the time and/or the PCM's RAM memory has died and it is "starting fresh" at every start up. A little probing of the sensors supply voltage should confirm the life or death of the quaddriver.
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Old 09-19-2002, 12:40 AM   #10
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UPDATE:
For ssicarman, satech and all who may encounter this weirdness again at some point. I (finally) got together with some buddies who still turn wrenches full time with my symptoms. ONE had seen this before AND someone on another board had expirenced the same thing in a Chevy PCM. Essentially what we have determined is that it is the "pull up" circuit in the PCM...more specifically 1 transistor in that circuit. Apparently this transistor is most commonly burned out by an improper jump start. Hook up jumper cables with the key in the "run" position and a dead battery in the car and the voltage spike from the other car's good battery promptly kills it. While I have never had to jump the car, the previous owner was...shall we say...not the brightest bulb on the xmas tree..anyway a new PCM is in order. OH, and ONLY the "pull up" cuircuit of the PCM is affected..the quad driver and all other functions remain intact..essentially what happens is the computer works just fine there just is NO way to ever "talk" to it again as the ALDL is rendered non-funtional. Just thought you guys might want to add it to your list of "things I've seen"
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Old 09-19-2002, 09:37 AM   #11
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Wolf:

(QUOTE)Essentially what we have determined is that it is the "pull up" circuit in the PCM...more specifically 1 transistor in that circuit. Apparently this transistor is most commonly burned out by an improper jump start. Hook up jumper cables with the key in the "run" position and a dead battery in the car and the voltage spike from the other car's good battery promptly kills it. (/QUOTE)

Amazing...your follow-up (update) just confirms what many of use have perceived---you ARE THE primary source for tech info. Relative to the burned transistor, I would assume that when the previous owner had a starting problem, he/she just had someone jump start, without his fully turning the key completely off -- actually, your problem alerts us to be mindful of insuring that before jump starting, be sure key if "Off".

Thank you so much for the detailed update.
Congratulations on your finds -- your sources must be considerable.
...
> 95 SL 2 = 653,369 Miles 40.4 MPG, as of 5/20/11. My manual Radiator Fan Switch, courtesy of Wolfman's patient installation guidance, continues to be.......invaluable < The car was retired
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