ECM Scan question
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,664
Likes: 0
From: Sonoran Desert of Arizona
ECM Scan question
I removed my TB this weekend, cleaned it, replaced all the gaskets, installed a new IAC valve, found and repaired a vacumm leak and then I hooked my scanner up to my '87 this weekend.
Looked at the TPS voltage( was right on) then scrolled down thru the menu and came across a line stating the trans was in first gear.
The trans was in park.
I read the Helms manual and it states the trans p/n switch sends a signal to the ECM telling it if it is in gear or not, and modifying the IAC to maintain set idle speed.
I got that part of the info.
What I didnt get was why the scanner says 1st gear, will it show any other gears, or is just a generic value relating to in gear or not in gear?
I ordered a new p/n switch, so if mine is truely bad I can change it out.
I doubt it is, as the starter will only work in p or n, and the back up lights only lite in r.
I suspect an open wire going from the switch to the ecm, correct?
Looked at the TPS voltage( was right on) then scrolled down thru the menu and came across a line stating the trans was in first gear.
The trans was in park.
I read the Helms manual and it states the trans p/n switch sends a signal to the ECM telling it if it is in gear or not, and modifying the IAC to maintain set idle speed.
I got that part of the info.
What I didnt get was why the scanner says 1st gear, will it show any other gears, or is just a generic value relating to in gear or not in gear?
I ordered a new p/n switch, so if mine is truely bad I can change it out.
I doubt it is, as the starter will only work in p or n, and the back up lights only lite in r.
I suspect an open wire going from the switch to the ecm, correct?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Maybe just the Scanner so you might want to look at whatever manual came with it. If I remember correctly, my Auto X-ray reads Park/Neutral vs Drive as a Yes/No on my '89 and it didn't make a whole lot of sense to me the first couple of scans. The important thing is that it switches from one to the other when you shift out of Park/Neutral into Drive and vice versa. For my other GM's (all with electronic autos), it reads the correct gear position, but there's a lot more data available. For my 700R4, I see something for Park/ Neutral and then a TCC field, but not much else. If your switch was bad, you'd probably have other driveability problems - like stalling when you put it in Drive. Since you've verified that the backup lights come on in Reverse and that it starts in Park/Neutral but not in Drive, it's probably working just fine. You could also see if the Load Variable increases when you put it in Drive and if everything is functioning correctly, Actual RPM - in Drive - should be +/- 50 RPM from Targeted.
Thread Starter
Drifting
Joined: Oct 2004
Posts: 1,664
Likes: 0
From: Sonoran Desert of Arizona
I picked up the new P/N switch this afternoon. Looking at it, it has 6 leads. I investigated further by reading the wiring diagram in the Helms and there is one pair for b/u lamps, one pair for p/n starter enable, and one pair for p/n confirm which must be the bad set of contacts in my switch. (or a bad lead or connection)
I'll post my results when I get finished with this little problem.
I'll post my results when I get finished with this little problem.
