V1 No Start Issue - B+ Terminal/Fuse Box

[Gtstorey]

I don’t know. Nothing gets powered because it’s all shut down when doing the no start. I could clear them while it’s reset though

I don’t think the codes are causing the no crank then. Check and see if you are getting power supply to the obd2. If nothing is powered up you have a wiring problem. The only final check would be to power the obd2 port straight off of the battery to try and enable communication.

 

[Robinjo]

I don’t think the codes are causing the no crank then. Check and see if you are getting power supply to the obd2. If nothing is powered up you have a wiring problem. The only final check would be to power the obd2 port straight off of the battery to try and enable communication.

I do not have OBD2 port power when the issue is occurring. I do not understand how unplugging the cables at the battery and not disturbing the wiring system is giving this still giving this condition. This seems more like something is resetting, not a connection problem.

 

[Gtstorey]

The obd2 port is not ignition on powered, it is full time power from what I remember.

 

[Robinjo]

But it gets power after the reset condition is what confuses me.

 

[Gtstorey]

Maybe you have more than one problem.

The only thing I can think of that could tie what should be basically a full time hot circuit to the ecm/bcm is a bad/corroded connection that carries current when cool/initial power, but fails after some time under load and has to completely cool by eliminating even parasitic draw before it will carry load again. That does seem a little out there. This is why you sometimes have to check continuity with test light/load instead of just a voltmeter though.

I would start with the wiring diagram for the obd2 power circuit and see where that is loosing power. I might be available to help this weekend if you can't resolve it.

 

[Desert Sasqwatch]

Believe the BCM controls the power to the OBD? Maybe you have something intermittent at the BCM, either a signal or a ground. Have you checked these connections?

 

[Robinjo]

I’m going to do a bit of investigation and see what I can find.

 

[Joebob]

I just went through a crippling electrical issue on my car last weak. Drove off a steep drop off +/- 4" and went into limp mode with everything from brake, cruise, transmission, communication, ect errors. It would run right for a few minutes but after 5-10 minutes or plugging anything into the OBDII port would again cripple it. Turned out to be a loose connector or pins in the BCM related to the CAN BUS tan/tan/BK twisted pair. For your symptoms I would:

1. Make sure anything not plugged in or wired up is not grounding out or shorting to ground. Tape all cut ends off conductive surfaces and each other. These computers are so interconnected that one thing can trip another.
2. Make sure you have great grounds at all locations.
3. Look over Bar-Air's plug wiring tables or Alldata to trace communication (high and low speed LAN) wires through the system to confirm continuity. They are not for your car but should be 90%

V1 - BAR-AIR's build up in Buffalo N.Y.

Yes those are 5 3/4” lenses. Just make sure they are the DOT lenses. Those were advertised as DOT lenses but when they showed up no DOT markings. Took about a month of back and forth with the manufacturer before they sent a set of DOT lenses. Nate’s car is using a set of 5 3/4” headlight shells...

dfkitcar.com

4. Watch this video to check the OBDII port and CANBUS system for confirmation all computers are communicating.

Let us know what happens and good luck.

Joe

 

[Robinjo]

I just unplugged the BCM power line at the battery connector, accidentally with key into run position and everything immediately lit up came on. So, it appears to be at the BCM end of things. I'll begin checking things here. Fuses, then connections, and then go further as needed.

Hopefully my BCM isn't rubbish, but I guess that would be easier than tracing every wire.

 

[Joebob]

I just unplugged the BCM power line at the battery connector, accidentally with key into run position and everything immediately lit up came on. So, it appears to be at the BCM end of things. I'll begin checking things here. Fuses, then connections, and then go further as needed.

Hopefully my BCM isn't rubbish, but I guess that would be easier than tracing every wire.

Be careful not to plug and unplug any computer under power or it can mess them up. make sure the battery is disconnected and depowered before plugging and unplugging things.

 

[Gtstorey]

Believe the BCM controls the power to the OBD? Maybe you have something intermittent at the BCM, either a signal or a ground. Have you checked these connections?

According to the diagram Ross posted here;
(4) No power to obd2 port | DF Kit Car Forum
The OBD2 is fed directly off of the lighter fuse with no connection to bcm/ecm or even a relay. Maybe Robinjo ran it off something else.
I know the newer models are ran off battery voltage. I think all GMs (and maybe part of the OBD2 protocol) are done this way.

 

[Robinjo]

Let me double check the no power condition. I have s better feel for the ports on the OBD2 plug after following the video posted.

 

[Gtstorey]

I doubt anything with the CAN is causing the problem, but here is most of the same info as the video, just written out.
SECTION ‘X’ CONTENTS (aeswave.com)

 

[Robinjo]

The video was actually quite helpful. It talked about then showed what to do.

 

[Robinjo]

According to the diagram Ross posted here;
(4) No power to obd2 port | DF Kit Car Forum
The OBD2 is fed directly off of the lighter fuse with no connection to bcm/ecm or even a relay. Maybe Robinjo ran it off something else.
I know the newer models are ran off battery voltage. I think all GMs (and maybe part of the OBD2 protocol) are done this way.

I just checked, I do have power at the OBD-2 port in terminal 16 eve while the no start condition is occurring.

 

[Gtstorey]

but no communication with the modules ecm/bcm etc? You need to study the wiring diagram for the power feeding the BCM and see how that is routing to to the BCM.

I wonder if there is any chance this is a key/ignition switch issue?

 

[Ross]

Here is all the wiring for the GM High Speed LAN. (Pin 6 to pin 14 on the OBDii port.)
Here is the wiring for the GM Low Speed LAN. (Pin 1 on the OBDii port.)

 

[Robinjo]

I did check the High and Low outputs that the video said. It checked proper. 2.6v high and 2.4 low, equaling 5v.

 

[Joebob]

Are you getting 60 Ohms at the terminals? That was my issue. LAN was connected to power steering but lost the ECU. Car would run until hit the error count threshold and then would go to limp mode.

 

[Gtstorey]

Maybe I’m miss understanding your symptoms. Does anything work when you turn the key? Fuel pump? Do you have relays clicking in the fuse box? Any lights on the instrument cluster?