New member- looking for help with code U0109 (no comm to FSCM) and overnight battery drain on my 08 Sierra

[DJPepper]

Hi folks, I've got a problem with my truck that I'm hoping someone can offer some guidance on. I've researched the conditions and search some forums but haven't found anything yet.

 

So 3 mornings ago I went to drive my truck and the battery was dead. I tried jump starting it and it turned over fine but wouldn't fire. It was cold in Northern Michigan so I thought I might have some bad gas and freezing in the fuel lines. I pit a heater on it the next morning and tried starting and the battery was dead again. I charrged it again and pulled a U0109 code. And others related to low voltage (those have cleared and not returned since not letting the battery die). So I haven't seen anyone have the battery and u0109 occur at the same time. Hoping someone has experience with the conditions simultaneously and can help track down the problem.

There is power at the fuel pump when I bypass the fscm at the plug. I've also tried a paraitic draw test by measuring voltage drop across fuses and nothing turned up. But when I put my ammometer in line with the battery ground I get an initial draw of about 2.4A that starts decreasing after 30 seconds and stabilizes at 20mA.

Any ideas would be greatly appreciated!

 

08 Sierra 1500 SLE 5.3L 4x4 with no mods and no sign of issues before this happened

[diyer2]

Figuring there is no battery drain issue from your testing.

I would replace the battery.

Check all grounds.

[tbarn]

20ma is excellent. Start with a charged battery. Clear all codes. Attempt to restart. See if U0109 comes back or cannot be cleared. If it cannot be cleared or resets you have a Fuel Pump Control Module issue or a wiring issue. These modules are a fairly common problem. Or it can be power, ground or network communication wiring problem. If you find it needs a fuel pump control module, it will need to be programmed.

[DJPepper]

Thanks for the replies guys. I was just doing some testing following the gmflash youtube channel. I'm only reading 12-18mV on both sides of the ecm probing the green and white wire that goes to the fscm. It's my understandings that it should be reading close to battery voltage. If thats accurate it seems like the problem could lie between the power center and the ecm. But I'll double check after the battery gets some charge. Any idea what ecm fuse to check there (I'm assuming it should be close to battery voltage at that point too)? I checked voltage at the fscm fuse too and its around 12V.

[DJPepper]

It's been a while, but I thought I would update this in case anyone happens to be in a similar situation. It turned out to be a bad FSCM. I have a tech 2 clone, but couldn't get the programming mode to work so I ended up taking to the local dealership to install and program. I tried taking it off myself but it was a real bitch (GM must put these on before the bed goes on) and high temps were 5-10°F in northern Michigan at the time. The dealer charged $289 for the install, programming, and a new acdelco battery; so it could have been worse. I ordered the FSCM online for under a $100 (forget where, maybe Rock Auto). That's the way to go if you can wait for shipping. My impression is that the bad FSCM was causing the drain on the battery. Everything has been good since then. To save yourself from having get towed to a dealer (and check that your fuel pump is working) just use a jumper wire on the fscm plug to send power directly to the fuel pump and you can drive it in (gmflash has the pinout for the plug). I used the fuel pump fuse as a power switch when I had things wired this way.

 

I tried diagnosing using the gmflash youtube video and a pinout on there website but it seems like some of the info was confounded and it turned out to be a waste of time. I would say if you have the u0109 code it's likely a bad fscm. My concurrent battery issue made me think I had a short  in that circuit, but it was the fscm all along.

[davester]

thanks for coming back and posting what the fix was.