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HELP!!! 95 Deville 10 amp Ign1 engine compartment fuse keeps blowing


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Please can anyone help?: 1995 Deville, fuse a3, 10 amp engine compartment fuse blows whenever I put car in reverse. If I start car from neutral fuse will not blow. Put it back in reverse it will blow. This fuse affects my gas guage which reads "E" once it blows and my automatic locks stop working, also, headlight chime continuosly sounds if I turn on lights. According to my manual this fuse powers: A/C refrigerant low pressure switch, Park/Neutral position switch, Instrument panel cluster, Sensing and Diag. module (SDM), Turn/Hazard signal switch assmbly, Chime module, Headlamp switch. I would think that it might be related to either the chime or the headlamp switch if not for the fuse blowing only when in reverse. Anyone have any ideas? Appreciate any help that you guys can give...

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There is a shift module on the driver side of the engine back toward the firewall down below the throttle body. An electrical conduit runs right by it, its possible that the cable/lever has cut into the harness and when you move it to a certain position it shorts out, I would check that first.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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There is a shift module on the driver side of the engine back toward the firewall down below the throttle body. An electrical conduit runs right by it, its possible that the cable/lever has cut into the harness and when you move it to a certain position it shorts out, I would check that first.

Thanks for the input, BodybyFisher, I'll check that out soon as this rain stops. The car is outside and I don't have access to a garage. But, and bear with me here please, I'm some-what of a novice at this, but is shift module the "proper" name of the part you're referring too? I have access to a service manual to pinpoint the location. Thanks...

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The proper name is the Park/Neutral position switch (PNP)

There is a lever there that moves, and that is the only thing that I can think of that can cause your problem, its obviously mechanical to me, as you can not start it in PARK and move it past REVERSE, but N is ok...

If that is not it, we can go on from there

Has any work been done on the engine, like crossover seals, tranny removal, etc?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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The proper name is the Park/Neutral position switch (PNP)

There is a level there that moves, and that is the only thing that I can think of that can cause your problem, its obviously mechanical to me, as you can not start it in PARK and move it past REVERSE, but N is ok...

If that is not it, we can go on from there

Has any work been done on the engine, like crossover seals, tranny removal, etc?

Hey BodybyFisher,

Thanks for getting back to me, I had this engine put in about a year ago (used) car has been running fine. Had a rear brake line go out so the car sat for a little while. Once I had the brakeline repaired discovered the battery had died, jumped it to bleed system, it started but died the next day. Then removed the battery and had it charged, put in and realized my problem with the blown fuse. Don't know if it started right after attempting to jump or after battery replacement, just didn't notice it until after work was done on brake system. Have a new battery in it now. I had a feeling that it might be in that PNP switch, that's why I was wondering if that's what you meant by shift module. Could the switch possibly be fried? Is there any way to test it before replacing it? Thanks for any feedback...

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When they put the engine in, its possible that they didnt route the conduit properly around that module, check that first. I think you would get a PRNDL code if it was fried, have you checked for codes?

It seems to be mechanical to me, check for rubbing on that nearby conduit first and lets see... I was under the impression that was called the PRNDL module

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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When they put the engine in, its possible that they didnt route the conduit properly around that module, check that first. I think you would get a PRNDL code if it was fried, have you checked for codes?

It seems to be mechanical to me, check for rubbing on that nearby conduit first and lets see... I was under the impression that was called the PRNDL module

No codes, so it sounds like it may just be mechanical as you stated. Just can't check it right now due to the rain (which isn't supposed to let up until 2morrow night) But, that's my starting point as you suggested and I'll post back my results once I do. Oh, and your impression is right it is called a PRNDL module, but as I stated "I'm some-what of a novice at this"...Lol I'll post back, thanks for the input...

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Hey don't sell yourself short, you have a factory service manual.... I hope someone confirms my thinking on the PRNDL module, I think its a neutral safety switch plus it gives info to the IPC regarding the gear selected...

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Hey don't sell yourself short, you have a factory service manual.... I hope someone confirms my thinking on the PRNDL module, I think its a neutral safety switch plus it gives info to the IPC regarding the gear selected...

I believe you are correct Mike.

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Hey guys, finally got a chance to check that harness that runs by the PRNDL switch, nothings rubbing or pinched, no wires chaffed or anything. What I did find out (from the service manual) is the PRNDL switch also controls the backup lamps. So, my thinking is, seeing that the only time the backup lamps come on is when the car is put in reverse, the issue may very well be in that circuit. Also, the ground for the PRNDL/Backup lamps common harness is (if I'm reading the schematics correctly) right in the vicinity of the brake line I had replaced before all this started. Possibly wire got pinched, scraped, knocked off? I had a "Back-yard mechanic" do the line so anything is possible. The only other thing I think it could be is the PRNDL switch itself, I'm gonna have a friend who knows electrical check it over the weekend, (even though I'm not getting codes) But in the meantime does anyone know for sure of a ground that runs under the car, rear, possibly drivers side? I'm not sure if I'm reading the schematics correctly and having trouble locating anything. As always any feed-back is much appreciated...

Edited by beuford0320
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