PCM and neutral safety switch
Thread Starter
7th Gear
Joined: Nov 2015
Posts: 7
Likes: 0
PCM and neutral safety switch
Can anyone explain the purpose of grounding the PCM terminal D11 through the neutral safety switch ? I cannot find a schematic or other info that explains this purpose.
Thanks, Richard.
Thanks, Richard.
Thread Starter
7th Gear
Joined: Nov 2015
Posts: 7
Likes: 0
SJW, thanks for your quick reply, however, that does not answer the query I'm in. I'd like to know what the purpose is, in grounding the pcm terminal D11 as it goes through the neutral safety switch. Does this in some way enable or disable some other feature by letting the pcm know that terminal D11 is now grounded ? Does this enable the starter relay by grounding terminal D11 ? Or -----?
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
What year are you interested in discussing and is it a PCM, ECM or maybe BCM/CCM?
Maybe if you have the service number off of the component itself. What are you attempting to use as a source for schematics. The more information you share the easier it would be to gather information.
Le Mans Master
Joined: May 2005
Posts: 7,362
Likes: 2,281
From: Central Maryland
You haven't said what model year C4 you're dealing with, but on my '94, the ignition switch feeds battery positive through a fuse, then through either the clutch switch (manual trans), or neutral safety switch (automatic trans), then through the coil of the start enable relay, and the circuit to ground is completed by a switch within the CCM (I don't know which pin without looking that up). The CCM won't close this internal switch to ground unless it sees the correct resistance of the VATS pellet in the ignition key.
Does this help?
Live well,
SJW
Does this help?
Live well,
SJW
Last edited by SJW; Nov 16, 2015 at 08:42 AM.
Thread Starter
7th Gear
Joined: Nov 2015
Posts: 7
Likes: 0
I'm pretty sure I'm using the right terminology for the powertrain control module as PCM.
It is from a '91 C-4 with automatic trans. The pass key/vats has been disabled through memcal reprogramming and the engine starts ok, but I noticed this one wire from terminal D11 that is not connected to the neutral safety switch. The only schematic I can find shows the wire connected between the neutral safety switch and terminal D11 but I can't find any info that explains it's purpose.
Thanks, Richard
It is from a '91 C-4 with automatic trans. The pass key/vats has been disabled through memcal reprogramming and the engine starts ok, but I noticed this one wire from terminal D11 that is not connected to the neutral safety switch. The only schematic I can find shows the wire connected between the neutral safety switch and terminal D11 but I can't find any info that explains it's purpose.
Thanks, Richard
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
I'm pretty sure I'm using the right terminology for the powertrain control module as PCM.
It is from a '91 C-4 with automatic trans. The pass key/vats has been disabled through memcal reprogramming and the engine starts ok, but I noticed this one wire from terminal D11 that is not connected to the neutral safety switch. The only schematic I can find shows the wire connected between the neutral safety switch and terminal D11 but I can't find any info that explains it's purpose.
Thanks, Richard
It is from a '91 C-4 with automatic trans. The pass key/vats has been disabled through memcal reprogramming and the engine starts ok, but I noticed this one wire from terminal D11 that is not connected to the neutral safety switch. The only schematic I can find shows the wire connected between the neutral safety switch and terminal D11 but I can't find any info that explains it's purpose.
Thanks, Richard
Mention the year and it will sort itself when asking questions.
Last edited by WVZR-1; Nov 16, 2015 at 09:25 AM.
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Thread Starter
7th Gear
Joined: Nov 2015
Posts: 7
Likes: 0
Thanks for all of those who came to my rescue in this situation and since this disconnect will not effect the normal operation of my TPI, I am grateful to find this out, especially to
WVZR-1. Thanks again, Richard.
WVZR-1. Thanks again, Richard.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
Snapshots if indeed a '28 Essex.
Thread Starter
7th Gear
Joined: Nov 2015
Posts: 7
Likes: 0
Yes indeed , it is a transplant into a 1928 Essex. I'm using the complete engine and transmission, including the original "ECM' and wiring harness. It's been job and a half to get things wired correctly. Finding reliable wiring diagrams and schematics has been a chore. I'm now down to a few remaining circuits to complete the job and get're fired up !
I want to thank you again for your support, Richard. Cana, Va.
I want to thank you again for your support, Richard. Cana, Va.
Le Mans Master
Joined: May 2005
Posts: 7,362
Likes: 2,281
From: Central Maryland
Yes indeed , it is a transplant into a 1928 Essex. I'm using the complete engine and transmission, including the original "ECM' and wiring harness. It's been job and a half to get things wired correctly. Finding reliable wiring diagrams and schematics has been a chore. I'm now down to a few remaining circuits to complete the job and get're fired up !
I want to thank you again for your support, Richard. Cana, Va.
I want to thank you again for your support, Richard. Cana, Va.
Best wishes with the project.
Live well,
SJW
Racer
Joined: Jul 2015
Posts: 313
Likes: 15
From: Modesto Ca
I like Alldata.com for wiring harness diagrams.Its basically the gm service manual online.Its $24 a year for 1 car.You can print what you want from the website.I just reworked an engine harness for a 2004 vette engine to go in a 57 chevy and all the wire colors and pinouts were accurate.
Thread Starter
7th Gear
Joined: Nov 2015
Posts: 7
Likes: 0
To odxr: I have a friend that has Alldata ( commercial version ) and we could not find the diagrams I needed. Good thing though, I've advanced beyond that need and am close to finishing my wiring. I'm into the lights, gauges and fuse boxes now, pretty basic stuff.
Also, Ive posted pictures of my project but can't find them on the site. What am I doing wrong ?
Also, Ive posted pictures of my project but can't find them on the site. What am I doing wrong ?
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
To odxr: I have a friend that has Alldata ( commercial version ) and we could not find the diagrams I needed. Good thing though, I've advanced beyond that need and am close to finishing my wiring. I'm into the lights, gauges and fuse boxes now, pretty basic stuff.
Also, Ive posted pictures of my project but can't find them on the site. What am I doing wrong ?
Also, Ive posted pictures of my project but can't find them on the site. What am I doing wrong ?
Last edited by WVZR-1; Nov 20, 2015 at 08:00 AM.