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Hey can someone help me out, I just swapped a P59 ECU in an 03 Sierra that had a bad pin on the fan control, fans where on all of the time. I put in a a P59 from an 05 Express, I have everything working, but the battery light is staying on all the time, even though the gauge is at 14, and the charging system is putting out 14.3 to 14.4.
Is there a we to turn off the idiot light and use only the gauge.
Did you flash the '05 Express PCM with a '03 Sierra OS?
Have you found out how to do this? I have a 2006 Silverado ss that the previous owner has molested the crap out of this truck and my idiot light stays on at all times. Alternator is good, voltage output is good but for some reason my light stays on and I would love to turn it off and just go by the gauge as well. Had the cluster rebuilt and when rebuilt found duct tape covering the battery light as gauge cluster is from a 2003 not a 2006 ss, so if I could turn it off that would be amazing.
Battery light is controlled over serial data, the 2003 IPC software isn't compatible with the signals being sent by the 2006 PCM. Sucks that everything works but that one little thing, but that's the fix, get the right cluster.
Isn't there something about '04 up alternators and ecu control using pwm?
I am just speculating based on looking at sample tunes and service manuals...
2003 alternator is PCM-controlled, 2006 has a 'Generator Battery Control Module' handling it.
There is a difference between '03/'06 tune files for 'Alt L-Term' under system options, I would assume that flipping that setting for a test won't permanently break anything.
But, I'm pretty sure the issue is caused by a '03 IPC expecting to see comms coming in from a '03 PCM connected to a '03 alternator via a '03 wiring harness, and instead the truck is talking at the IPC in 2006-speak.
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I really don?t want to buy another cluster just to make this light turn off.
I?m a full on noob and quite slow when it comes to this stuff but really want to learn more. I thank you for this so far and will try to figure out what you said haha so I can see if changing a setting will shut the light off.
I just fixed this in 3 trucks
First thing is see if you have 1 or 2 wires in the 4 pin plug on the Alternator.
All the ones I did had 1 wire (brown)
Now under system make sure Alt F-term is 0
Then go to engine diag and scroll down to code p1638.
Make sure SES is unchecked and mil is set to No code reported.
The battery light should work correctly now.
Anyone come up with more of a solution for this? I have a 2003 Sierra converted to 2 bar o/s running a turbo. Everything runs great. It has electric fan conversion on it with pcm controlling it. Randomly while driving the pcm will command the idle high and hold it there. This can happen while moving or stopped. Its not a hanging idle, the commanded idle rpm actually rises to 1000 rpm and holds there for 2+ minutes until it starts to come down. There is nothing in the idle settings to account for whats happening, has to be something in the background we dont have access to.
Thinking that it may be something related to the fans and the fact 2003 did not come factory with them, I flashed in a 2005 o/s with all of the data from the 2003 file copied across. No more high idle. But 2 other things have showed up. 1) cant turn the battery light off on the dash. Ive tried every combination of settings to try and make it go out, no success. 2) the engine now cranks over slightly longer to start. its not by a lot, but its noticeable.
Anyone have any insight?