Please Help: Crank, but no start

[Twisted Illusionz]

I am having a problem with my 05 z71 suburban. It was driving fine, shut it off after getting home from work. Went out a couple of hours later and now it will crank and crank and not start. If I stop trying to crank it and go to try again it won't even try to crank. Then if I shut the truck and lock it, then unlock it allows me to crank it again, but only the one time. I tried scanning it, but it shows that it can not communicate with the ecu. I'm thinking new ecu, but would like some suggestions please. I checked all grounds and fuses already.

[hatzie]

No PCM comms means the PCM doesn't have power or the CAN, Class II serial data, power, or ground are not present on the diag port. 2007 & earlier likely do not have CAN.

Check for power and ground on the diag port with a meter. DO NOT plug a meter into terminal 2, 6, or 14 of the J1962 port.
Check for power at the PCM connectors. You're going to need to get some service information on this. Probably will require a purchase from Alldata DIY or Mitchell or ...
You can check at terminal 2 for serial data with a logic probe or oscilloscope. DO NOT plug a meter into the serial line. This is not RS232 serial. You can let the magic smoke out of the UART on the PCM.

This is the government mandated DLC, OBD II port, SAE J1962 port, Diag port, ...

• Terminal 2 is the Class II Serial data from the PCM BCM Radio ...
• Terminal 4 is the diag port ground
• Terminal 5 is the PCM ground
• Terminal 16 is BATTERY positive power

If the truck has GMLAN (CAN) like my 2009 Impala

1. Terminal 6 is CAN +
2. Terminal 14 is CAN -

[AussieinNC]

Check the ground connection under the drivers door on the chassis...remove the bolt and clean it well....cut the terminal ends off and replace them, soldering on new connectors.