GMC Troubleshooting Questions? Ask a Mechanic for Answers
Let's see if we can get you going again.
First, can you check the PCMB fuse to see if it's blown?
Also, check the fuel pump relay for signs of excessive heat.
Verify the "IGNA" 40 amp fuse in the Underhood Electrical Center (UHEC).Check for voltage at the Red wire at the Ignition Switch in pin F.If no voltage is present, check pin A10 at connector C201 at the base of the steering column.If no voltage is present, check the bottom of the UHEC for rodent damage.Check the Red wire in 68 cavity Gray connector at pin B12.If voltage is present, replace the Red wire circuit #142.
It's in the ignition switch connector.
Sorry, the UHEC is just the book's way of saying under hood fuse box.
Right, pin F feeds voltage to the ignition switch.
You would only need to replace the red wire circuit if there is no voltage at the ignition switch. The #142 circuit is at the PCM.
Do any other electrical circuits work? Door locks, power mirror (if equipped), power window etc.
How do the IGN0 and IGN3 fuses in the under dash fuse box look? Do they have 12 volts with key on or off?
When you first turn the key to the run position can you hear the fuel pump run for a few seconds?
When you jumped the starter to get it to crank did you have the key in the run position?
If you jumper the fuel pump relay will the pump run?
Jump pin 30 and 87 together. It should run the pump.
You should also be able to jump pin 30 and 87 together on the starter relay to get it to crank.
Do you have a scan tool to check for communication with the PCM and BCM?
I'm leaving the shop in a few minutes here, I might have to catch back up with you this evening.
Can you command the fuel pump to run with the scan tool?
No comms huh? Might be a PCM problem. Let me look at the schematic and see where we should look next.
1. Locate the splice pack SP205, which is taped to the harness above the left side footwell light under the Instrument Panel (IP) on the left side near the back of the fuse block.2. Remove the "Comb". Connect a scanner to the DLC. Use a suitable jumper to short pin D, a Purple wire to the Dk Green wire at pin B. Attempt to communicate with the Powertrain Control Module (PCM).3. If communications work, use another jumper to short pins B and D to each of the other pins in SP205 one at a time. Determine which wire/module is causing the communications failure. When that wire/module is shorted to pins B and D, the scanner will go to "No Communications".4. Go to that module for a circuit failure in the Class 2 data circuit or power or ground issue going to that particular module.
My guess is that it's the IPC- Pin G
If you don't get any communication in step 3, then there is probably a PCM problem.
That is worded kind of weird. The scan tool plugs into the Data Link Connector like normal, not the SP205. You just unplug SP205 and jumper the pins while you have the scan tool plugged into the DLC.
Check the connector at the BCM for corrosion or water intrusion. All of those codes have to do with the BCM connector.
You should also check the ground point at the back of the engine; that point to the U1305 code. It's right at the firewall on the transmission bell-housing or the cylinder head.
Just to the right of the column. Here is the replacement procedure. It shows where the connectors are. I would pull the connectors and put some dielectric grease in there and then plug them back in.
So will it crank now that the communication network is back up?
I didn't realize you hadn't yet jumpered the other module pins. I thought you meant it just started communicating again.
You will want to jumper the other pins one at a time to the b-d jumper until the scan tool drops communications.
Whichever pin it drops communications on has a faulty corresponding module.
You need another wire to jump from those two to another pin in the connector. Going from B to D just wakes up the network.
This should be the SP205 pin out view. This is where the jumper from b-d is currently right?
I forgot the attachment.
From there you jump to each of the other pins one at a time while watching the scan tool.
I would probably start by jumping b-d to pin g. Then check communication. The most common fault on these trucks is the IPC.
Instrument panel cluster. If it dropped comms when you jumped to that pin then the short is in the instrument cluster.
The mileage is the only thing that won't be correct. It should allow the engine to start if the connector is the same on the 2002. I couldn't say off hand whether they are the same.
You might even be able to start it if you unplug the cluster connector. I know the 2000 and back models will start with no cluster; never tried on a 2004.
It's worth a try since you can get the cluster out in about 2 minutes on this one.
Disconnected or with the 2002 IPC?
Did your communication come back at the scan tool?
How do the wires look under the underhood fuse box?
It's a good place for rodents to chew wires.
You can remove the plastic cover and pull the box up and see all of the harnesses underneath.
Here is the starting circuit.
I'm sorry I didn't notice your response the other day. Your question dropped onto my timed out list for a lack of rating.
I'm not showing a pats option on the 2004 2500hd. That could be wrong though. What does your key look like? Is it black with the little plus symbol on the key?
Your question has dropped to my timed out list for a lack of a positive rating. This also means that I have not been compensated for my time; we initiated this conversation a month ago.