1995 Saturn SC2 Wiring/PCM issues

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2 months 1 week ago #201896 by SiameseClint
1995 Saturn SC2 Wiring/PCM issues was created by SiameseClint
Hey guys, New here to the forum. Long time ETCG subscriber. Mechanic of almost 20 years.

Anyway, I'm having an issue with my fathers 1995 Saturn SC2 w/MT. I guess I'm what you would call a "Honda-Head". So I'm more familiar with troubleshooting and fixing Japanese cars. So American GM based standalone Saturns from this era are a little perplexing to me.

I have a solid SES light on. And the Idle control motor/speed sensor/speedometer are not functioning. However everything else in the gauge cluster does work. RPM, Fuel, and temps are all reading fine. I tried replacing the IACV, speed sensor and eventually gauge cluster with new or known good units. No change. Checked voltage at IACV and speed sensor harness connector with Key on engine off, and Key on engine on. Increased throttle. shifted through gears with the wheels off the ground. I tried the IACV re-learn procedure. No change. No voltage at the connectors. Major bummer after buying the new parts and still no fix. But before the purchase of said IACV motor, I checked the old unit and the plunger was frozen in place. the old unit was toast. The speed sensor Had a little bit higher resistance than the new unit. And it was decades old. So replacement was warranted regardless.

usually I would just try to read DTC codes. Read forum posts . Watch videos and the sort when I am in unknown territory. But the first step in diagnoses is failing me.

No communication from the OBD1 DTC port. I checked with a multi-meter and there is voltage getting there. I even checked the SES light bulb that is supposed to flash the codes. And that is in working order.

I kind of already know where this nightmare is going. Either wiring harness or PCM issues. But I really hate trouble shooting wiring harness issues in an engine bay that hides the harness underneath everything. So basically everything on top of the engine needs to come off to get to it.

I guess what I'm looking for is someone who has had similar issues with OBD1 Saturns that might be able to lend some experience my way.

No idle control or speedometer really sucks. And my dad works 10 hours a day. And drives his car to work everyday. So I only have a limited amount of time to stick my head under the hood.

So anybody with knowledge of OBD1 Saturns would be wonderful.

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