[Gmecm] Missing cam position signal in 1228253 ECM

[Scott Feaver]

I have an 89 Lesabre, and had to replace the ECM once before.  Not sure if they are common to go, but I wouldnt rule it out...  The problem I had was the oxygen sensor input would occassionally peg right to 1120mv, even with the O2 sensor disconnected.   Swapping out the ECM fixed it right up :)

Scott
  ----- Original Message ----- 
  From: kevin spears 
  To: gmecm at diy-efi.org 
  Sent: Wednesday, May 11, 2005 9:01 PM
  Subject: [Gmecm] Missing cam position signal in 1228253 ECM


  I hate to burden the list with such a (seemingly) mundane question, but here goes.  I just picked up an 88 Park Avenue with a 3800 SFI V6.  It has a 1228253 ECM running ANBH 2522 code.  It runs, but has a persistent fault code 41.  According to the shop manual, code 41 indicates the ECM cannot see the signal from the camshaft position switch.

  I followed the troubleshooting chart, and am convinced the signal is getting to the ECM.  I put a scope on the signal wire and got a waveform trace that seems roughly like what I would expect to see.  It is a VERY dirty squarewave.  I took a picture of the trace on the scope if anyone is curious :)  As further proof, I tried starting the car w/o the cam switch connected, and it won't run at all.  It turns over and fires for approx 1 second, but then dies right out.  With the sensor connected it starts and runs.

  Anyway, the shop manual says that if a signal is present at the ECM harness, then the ECM is bad and should be replaced.  Seems a bit odd to me, as past experience has shown me that the ECM is usually the last thing to fail!  Especially on a motor that runs fairly well like this one.

  Does this ECM have a bad reputation for failures?  I suppose it wouldn't be difficult or costly for me to bring one home from a junkyard to compare results with, but if there's something else I've overlooked I might as well try it first!



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