Please Help: Crank, but no start - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Twisted Illusionz · 08-21-2023, 08:13 AM

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** · 08-21-2023, 06:14 PM

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, ...
Name: OBDII port 2005 Silverado.gif
Views: 139
Size: 19.7 KB

Name: OBDII port 2005 Silverado.gif
Views: 139
Size: 19.7 KB

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

Terminal 6 is CAN +
Terminal 14 is CAN -

**AussieinNC** · 10-05-2023, 06:23 PM

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.

08-21-2023, 08:13 AM	#1
Twisted Illusionz Registered User Join Date: Feb 2012 Location: Waller, TX Posts: 5	Please Help: Crank, but no start 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.

08-21-2023, 06:14 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,915	Re: Please Help: Crank, but no start 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 Terminal 6 is CAN + Terminal 14 is CAN - __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful. Last edited by hatzie; 08-21-2023 at 06:21 PM.

10-05-2023, 06:23 PM	#3
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,157	Re: Please Help: Crank, but no start 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. __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.