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Old 12-10-2009, 11:02 AM   #1
Jbauer
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Default Super weird SCT problem (SCT cant even help!)

Hey guys check this out.
I have a tune installed on my car... so i go and try and take the tune off yesterday..i plug the SCT tuner in.. it wont turn on... the odometer reads - - - - -..like it should, but the tuner itself wont turn on or make that noise it should make when powering on.

So i try it on 3 other cars...this frikin thing turns on and works just fine on all there cars..but when i plug it into mine..it wont work!!!

so i figure my OBD port is the issue...so i check all my fuses..all are fine. So i go to autozone to see if there scan will power on with my OBD port...it DOES! ...emissions test... plugs in and powers on the emissions testing computer just fine... go plug in SCT tuner.. EPIC FAIL!

WTF!! The good ole' boys at SCT are stumped, and so am I. what on earth!
Can anyone offer me any help!?!

Thanks
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Old 12-10-2009, 03:39 PM   #2
cliffyk
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The only thing that occurs to me is that while pins 4 and 5 of the OBD2 connector are both ground, they are separately wired as pin 4 is technically the chassis ground, and pin 5 is the signal ground.

A scan-tool or tuner should connect to both pins, however I have seen many that do not and only connect to one.

If the SCT tuner only uses one (pin 4 or 5), and the pin or wiring for that pin is damaged, then the SCT would not have a ground connection on your car and therefore not power up. Other OBD2 tools might still work correctly.

On our cars pin 4 is a black wire tied to a chassis ground point (G204), pin 5 is a black/yellow wire connected to G104 which appears to be a hard-wired homerun back to the battery.

Has your negative battery terminal wiring been changed?
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New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


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Old 12-10-2009, 05:29 PM   #3
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edit, nvm didn't read your whole post about the fuses.
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Old 12-10-2009, 05:44 PM   #4
Jbauer
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cliffyk, i did have a radio/amp/sub installed....

What should i be doing, as i dont know jack squat about electrical except the basics?
where is g204 and g104s location? i'll take a look at it and bring intel. back as to how they are wired with pics and stuff.

Thanks so much!

Last edited by Jbauer; 12-10-2009 at 05:48 PM.
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Old 12-10-2009, 07:13 PM   #5
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Quote:
Originally Posted by Jbauer View Post
cliffyk, i did have a radio/amp/sub installed....

What should i be doing, as i dont know jack squat about electrical except the basics?
where is g204 and g104s location? i'll take a look at it and bring intel. back as to how they are wired with pics and stuff.

Thanks so much!
I'll get some info together tomorrow. SWMBO wants to go out to a late dinner now...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum,
Delta Force tuned, Steeda UDPs, Ralco flywheel,
RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


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Old 12-10-2009, 11:27 PM   #6
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Thank you so muchr, i really appreciate this!!
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Old 12-11-2009, 06:31 PM   #7
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I haven't forgotten about this--just busy with working and paying bills an stuff..
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum,
Delta Force tuned, Steeda UDPs, Ralco flywheel,
RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


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Old 12-11-2009, 06:56 PM   #8
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understood, thanks again
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Old 12-13-2009, 02:07 PM   #9
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You need to check the wiring to the OBD2 port (DLC, Data Link Connector) and make sure nothing has been cut/broken/pulled-out, etc. Also look at the face of the DLC and make sure no pins are messed up (I have seen them get pushed in).

Here's a DLC pin-out diagram for our cars:
Click the image to open in full size.
Our cars have only the pins highlighted in yellow. If you have a multimeter set it to measure voltage and check between pins 4 and 16, then between 5 and 16. You should get a reading of 12.0V or more on both tests--if not then, and one reads +12.0V and the other does not then the ground pin providing no reading (either pin 4 or 5) is not wired properly.

The key does not have to be ON to make this test, the +12.0V supply to pin 16 is always on...

If you don't get +12.0V on either test then the power to pin 16 is disrupted--it is powered from fuse #31 (10A) in the Central Junction Box (under the dash).
Click the image to open in full size.

Don't worry about the G104 and G204 grounds right now, report back on what you find.

If you don't have a multimeter you can buy one most anywhere these days for $20 or less. Harbor Freight, if there's a store nearby, has a perfectly serviceable small digital meter for under $5. Even a 12V test light would work...
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SOLD! - 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum,
Delta Force tuned, Steeda UDPs, Ralco flywheel,
RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.

New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq


Engineering is, at its base, making what you want from what you have.
At its extreme it is making what you want from what you can get.
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Old 12-14-2009, 01:17 AM   #10
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ok so i use my test light and pin 1 is the only one getting power...maybe the connector is upside down and pin 1 is actually 16...so i go with that... and i get the meter out.

i test between the first pin (which i'm assuming is 16) and pin 4... i get LESS than 12 volts but not 0. I do the same thing to pin 5...and it says Overload...

Last edited by Jbauer; 12-14-2009 at 11:11 AM.
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Old 12-14-2009, 01:17 AM
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