PCM Relearn?

Tiny
LABGUY
  • MEMBER
  • 1996 CADILLAC SEVILLE
  • V8
  • FWD
  • AUTOMATIC
  • 138,000 MILES
Before going out of town for 1 week I removed the connection to the negative terminal of the battery of my 96 Cadillac Seville SLS, so as to prevent power drainage. When I came back, I connected the battery again and noticed that the car was hard to start (took a couple of cranks before it started). After that first start everything was fine. However, the next day I noticed the same problem (hard to start) in the morning when I first try to start it. Took it to a mechanic and he said the battery was not holding the charge so I had it replaced. The next morning… same problem! So I took it again to the mechanic and he said the battery disconnection may have affected the computer as it gave a P0603 code; so he reset the code. The next morning… same problem. It seems that the problem appears only in the morning during the first start of the day but after the first start everything is fine!

Last Sunday night I parked the car in the mechanic's shop parking lot so that he could start it first thing in the morning and see what I am talking about. Monday morning came and when the mechanic tried to start it, it miraculously started at the frist crank (although it was around 3 seconds delayed). Something it hasn't done since the old battery was disconnected! The next morning, when I started the car, again, it started at the first crank but around 3 seconds delayed. This morning, when I started it. Its as if it never had any problems as it started normally. Did the PCM just relearn? (Mechanic told me before that there seems to be no problem with the FPR as I suggested to my by someone else.)
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Thursday, March 3rd, 2011 AT 6:33 AM

3 Replies

Tiny
FACTORYJACK
  • EXPERT
There is typically no relearn that happens that will affect startup. The concern you are describing, was it a noticeably slow crank, meaning a slow engine speed, or was the cranking speed fine, it was just a delayed start? A P0603 will set with a battery disconnect, may set erroneously, or with PCM power interruption, and does not necessarily affect the computer. Coincidentally, was there new fuel added, and the cold start issue may have been a result of fuel quality?
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Friday, March 4th, 2011 AT 5:11 AM
Tiny
LABGUY
  • MEMBER
The cranking (speed) is fine, its just that during the week that it was acting up (on the cold morning starts), it would need around 2 cranks before it starts. But as I said, for the past 4 days now it has been good. Just 1 crank and these past 2 days it's as if there was nothing wrong it. I don't think it would be the fuel because I always put in premium fuel. It pretty much healed itself but I am just wondering why this happened for a few days in the first place after I disconnected the battery for a week. I find it really strange.
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Friday, March 4th, 2011 AT 6:30 AM
Tiny
FACTORYJACK
  • EXPERT
Premium fuel can have ill affects, as with any other of the grades, it all depends on the volatility, and cold starts is when your most apt to see an issue. But that is not saying that it was truly the issue, just a possibility. The conditions that affect start time are adequate fuel pressure, injector pulse, spark timing(in relation to cam sensor determining when #1 is at compression stroke), and spark itself. If it is back to operating correctly, it is hard to say what specifically caused it. I have not seen a situation where a releaarn had to be accomplished before the vehicle would start correctly. For 96, things that could be relearned after power loss were shift adapts, and possibly fuel strategy. These would occur after closed loop was attained and the vehicle was running on sensor data, as opposed to defaults associated with open loop operation. Idle learn is also possible since that vehicle has an IAC valve, that should be done rather quikly, as opposed to over several days.
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Friday, March 4th, 2011 AT 6:46 AM

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