FICM Failure??? Code P1658

[03LB704.5LLY]

Hi guys so I was driving my Lb7 to Daytona (it’s about a 2 hour drive from me) to pick up some parts for my work truck. So I was going around 70 on the interstate when my truck had a decrease in speed and the CIL came on. I pulled over and shut it off to see if I could find the issue. It was running like it was in tractor mode (like a 4 cyl diesel) the only time I have heard a change in the engine similar was when the pigtail to the engine temp sensor failed so I pulled it off and ice picked it and put it back on. It started normally but CEL still on and showing no fuel although I had a full tank. I took off down the road for 5 minutes or so and the tractor mode came back. I was able to slowly drive (15mph) to an Autozone two miles away to get a code read out (below). I got my truck home after realizing that if I let off and eased into the pedal the trans would shift. Top speed was around 45 but I made it home. Now two days later (FICM en route via rock auto) I went to start and move my truck and it will crank normally but not start. It’s got me worried that another issue is the cause but I read that p1658 can only be caused by an internal error in the FICM. Any help would be appreciated as I do not want to jump down a rabbit hole on this truck. I have just replaced the bed, put new wheels/tires, and made it look very much like a new one inside and out.

Codes present
P0202
P0203
P0205
P0208
P1658
P2149

All codes are listed twice on the readout

 

[2004LB7]

Before condemning the FICM, I would check all the injectors listed (2,3,5,8) for shorts or bad wires. Maybe pull the connectors off the ficm and prob the injector wires there too to see what resistance you get and check to ground also

 

[03LB704.5LLY]

Before condemning the FICM, I would check all the injectors listed (2,3,5,8) for shorts or bad wires. Maybe pull the connectors off the ficm and prob the injector wires there too to see what resistance you get and check to ground also

Do you have a schematic to show which wires are which?

 

[Ron Nielson]

Wiring diagrams available here: https://www.gmupfitter.com/pdflists/view/6

 

[TheBac]

Check every wire in the harness just off the FICM right behind the alternator. Known problem area. You've probably got a wire cut/chafed there that is grounding out.