04 ECM with 05 5.3 -- "Battery not Charging"

[xEtherealx]

I am using an 04 ECM to run an 05 5.3l and everything seems to be working well except the charging system. I'm positive that the issue here is not with the charging system but rather the ECM or tune.

I know that there were some alternator changes from 04-05 but I don't know enough to know if it's something that I can tune around. If I recall, the ECM monitors voltage and calls for the alternator but I don't see any parameters around this in HPTuners.

Any ideas about what I should look for?

Readings when scanning are as follows:
DTC: P1637
Generator F terminal: 40-50%
L terminal: Always 'On'
Light: Always 'Off' (even though the light is intermittently off and on

[2xLS1]

If you are using a 04 OS then under the System Options set the Alt L-Term to 0. In Engine Diagnostics DTCs set P1637 to No Error Reported.

[xEtherealx]

If you are using a 04 OS then under the System Options set the Alt L-Term to 0. In Engine Diagnostics DTCs set P1637 to No Error Reported.

Thank you; Alt L-term is already 0 for all platforms, Alt F-term is 1 for GMT800. I copied that entire table from an '05 firmware and pasted it into the 04 table. One thing I did notice was that the source "Not Used" column was all '255' but when I pasted the values I couldn't set them to 255, which kind of makes sense if the value is a single byte. I think that probably is irrelevant here though.

Should setting P1637 to no error reported make the difference then, since I had L-term already set to 0?

While I've got your ear, is that table documented anywhere? I can't find info on it and similar inquiries had no responses, such as this one https://forum.hptuners.com/showthrea...Options-Matrix

[2xLS1]

Don't know what to tell you. Every 04 file i look at has Alt-L set to 1 along with Alt-F. 05 only uses Alt-F with P1637 set to No Error Reported. Your 04 should have had Alt-L set to 1 stock unless you had already changed it.

<Should setting P1637 to no error reported make the difference then, since I had L-term already set to 0?>

Why don't you just try it?

[xEtherealx]

Don't know what to tell you. Every 04 file i look at has Alt-L set to 1 along with Alt-F. 05 only uses Alt-F with P1637 set to No Error Reported. Your 04 should have had Alt-L set to 1 stock unless you had already changed it.

<Should setting P1637 to no error reported make the difference then, since I had L-term already set to 0?>

Why don't you just try it?

Maybe I wasn't clear, the 04 file did have Alt-L set to 1 and I had already changed it when encountering this error.

I'll disable the DTC to see if that helps but though I'd ask if I should expect it to work or not, given that Alt-L is already 0.