L5P trouble codes, need help

Rreeck43 · March 19, 2023

Hey guys, I’m new here and I’m looking for info. I have a 2018 L5P and It has custom tuning and has for the last 2+ years and 25k+ miles, I was driving the other day and it went into limp mode, it’s throwing 3 codes P0046 U18A2 & U0076. I have the can bus dummy plug and nox sensor plugs on the truck. I have replaced all 4 plugs just for safe measure as I live in northern Wisconsin where the salt gets at everything. I called my tuner and they said it’s not a problem with tuning but the truck. I’m thinking maybe it could be a bad turbo actuator? Or could there be just a broken wire somewhere in the harness for the canbus? My fuel gauge does not work, turbo builds no boost and I don’t have enough fuel pressure to get over 2k rpms. Any help and info would be great! Thanks!

newdude · April 26, 2023

U18A2 is Lost Communication with Fuel Pump Driver Control Module.

U0076 is Control Module Communication Powertrain Sensor CAN Bus Off.

P0046 is Turbocharger Boost Control Position Performance.

In the schematic, the ECM, turbo VGT actuator, reductant control module, NoX 1 and 2, exhaust particulate filter and fuel pump driver control module are all on the same CANBUS/GMLAN wire network. The network circuits they all share are circuit 4498 which is a blue wire with brown stripe (GM LAN +), and circuit 4499 which is a white wire (GM LAN - )

So if the VGT actuator were bad, it could be breaking the communication chain on that. You could have an open or shorted wire somewhere on those two circuits also. So those two wires would need to be properly tested at each component to see if the circuit has full integrity, or if there is a bad spot.