Dead BCM? Effed Passkey III? No start on '05 Montana

Mooseman

Original poster
Moderator
Dec 4, 2011
26,007
Ottawa, ON
I've been helping a friend for the past two years (yes, two years!) on and off to start this van. I am usually pretty good in this type of stuff and for the first time ever, I'm stumped and hoping that the vast knowledge in the Nation can help me.

2005 Montana van (non SV6) with the 3.4L. About two years ago, it was left sitting for a few months and the battery died. He charged it up and when he tried to start it, it wouldn't start nor crank. He thought it was the starter so replaced it, same thing. I did some troubleshooting. Checked if the fuel pump running when turning on the key, no. Checked all fuses, all good. Checked relays, all good. Fuel pump works when relay terminals are shorted. Starter cranks when solenoid shorted with screwdriver. When I tried to connect with my code scanner, would not connect, all I get is "Link..." and nothing happens. Aux power and all fuses good. He had an aftermarket remote starter and it couldn't start it neither. Disconnected it, including the Passkey bypass, no change. At this point and we give up for a year. We have another go at it last year. Basically went over the same things as last year but at this point suspect a dead PCM due to the lack of communication. So he orders a pre-programmed PCM with the VIN off eBay. Sits for another year.

Before going at it today, I did a bunch of research on the Passkey III system in this vehicle. It cuts off fuel and will not crank if the wrong key is used or if the system is defective and is the source of many problems for no starts exactly like this. It does not cut off ignition. Armed with this info on this PITA system, swapped the PCM, did the security relearn as per included instructions, nada. During the relearn, the security light is supposed to go out after 10 minutes, it never did. Even waited 20 minutes, never went out. Still no communication to the PCM with the scanner. So, I then checked for spark while cranking and it does spark, which tells me that the PCM is alive. Put in some fresh fuel in the tank. So I bypassed the fuel pump relay to force the pump to work, which would circulate fresh fuel into the fuel rails via the pressure regulator. turned on the ignition and cranked it, no start. I figure the PCM is also cutting off the fuel injectors since there is spark. One thing we did notice today is that the radio is giving a "calibrate" message briefly when it's turned on but still works fine. Even the presets are still there.

Without access to a Tech2 (which might not work anyway), we're just shooting in the dark with this thing. I am suspecting either a defective BCM or Passkey module or possibly one of the door modules screwing up the data bus. Everything in the van works except for the rear wiper and washer pump. Before suspecting the liftgate module (as far as I can tell, there isn't one), the liftgate lock works along with all the other locks. I am suspecting that the BCM is the cause since the radio seems to be having issues with the calibrate message. And if I'm not mistaken, the OBD2 port goes through the BCM to get to the PCM. We could tow it to a dealer and if they find the problem, will want to use only new parts supplied by them and their labour at $100/hour to install it and then program it even though a good used one will do the same.

If anybody has any ideas, please help me. :confused:

PS: thank goodness I disabled this anti theft crap when I got my tune.
 

MAY03LT

Member
Nov 18, 2011
3,426
Delmarva
Mooseman said:
When I tried to connect with my code scanner, would not connect, all I get is "Link..." and nothing happens.

Does your scanner read CAN? I've seen non-CAN readers give a link error message when trying to communicate with CAN vehicles.

Put in some fresh fuel in the tank. So I bypassed the fuel pump relay to force the pump to work, which would circulate fresh fuel into the fuel rails via the pressure regulator. turned on the ignition and cranked it, no start. I figure the PCM is also cutting off the fuel injectors since there is spark.

There is a way to verify injector pulse (or, in this case, lack of) without one of those noid lights. Install a pressure gauge and use a jumper to pressurize the rail. Take off the jumper. When cranking, watch what the pressure gauge does.

Without access to a Tech2 (which might not work anyway), we're just shooting in the dark with this thing. I am suspecting either a defective BCM or Passkey module or possibly one of the door modules screwing up the data bus.

It seems to me that too much stuff works to suspect a bus fault. We had a case the other day where an audio adapter pulled down the bus, and the symptom list was massive.

Let us know what the deal is with your scanner and we'll go from there.:cool:
 

Mooseman

Original poster
Moderator
Dec 4, 2011
26,007
Ottawa, ON

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