06 LLY engine control issues

[Leesnitz]

Hi friends. I have an '06 lly that has some ecm/ecu issues.

The engine will start itself while sitting still. I first noticed it after driving through a hard rain which makes me think its a matter of the computer getting wet and short circuiting. I disconnected the batteries for a little while and after sitting for a couple hours I reconnected them and things were fine. That problems has evolved into a constant issue though (wet or not) so these days when the batteries are connected, the starter will engage and the engine will run (sometimes poorly) until i disconnect the harness at the ecm.

More recently, it is having security issues. The engine will start, run for a minute, and then stop (with the security light flashing on the dash board). After a couple of starting cycles it will usually start and run (but the security light will either stay on or flash) but it will stay running until I disconnect the ecm.

Does anyone know how the ecm turns off the engine? Does it cut power to the FICM? Or perhaps the FPR? I'm looking for a bypass method for testing purposes. In theory- if it works that way, I could supply power to the FICM or another administrative device and keep it running, or turn it off while isolating the ecm issues.

Thanks for the help!

 

[MarkBroviak]

If it is an 06 then it is actually an LBZ and doesn't have a Ficm. The injectors are controlled by the ecm itself. You have a security system problem and a separate issue along with it. I would first check it for a remote start system. Other wise you have an issue with ignition switch or a fuse box is shorted out.

 

[Leesnitz]

It is definitely an lly. VIN code 2. Maybe they only put that in vans for that year, idk. Its an Express 2500.

The security system issue makes sense though, but im thinking that the ecm is married to the bcm and miscommunication or non matching flashes would behave similarly. Both are the original components so that shouldnt be the issue, but the way this thing behaves... its hard to say.

Just fishing for possible causes.

 

[zakkb787]

Doo a little searching. Cause I have one. It’s an LLY according to the vin yes. But it’s an lbz engine and 6 speed trans with an lly tune.

 

[rfletes79]

Look for the ficm, let us know if you find one.

 

[JoshH]

Sounds like maybe you have a faulty starter relay or a wiring issue to the starter relay.

I wish GM had come up with a new RPO code for the '06 LLY because it causes a lot of confusion. You should just call the motor an LBZ. It will make things much simpler when ordering parts or seeking help. You should also let people know it is a van right away because that makes things a little different also.