ricklovin93

The high speed GMLAN serial data buss uses two 120 ohms terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected at the data link connector (DLC) end of the link and the other is at the engine management module, engine control module (ECM) or powertrain control module (PCM), end of the link. The DLC terminating resistor resides internally in the body control module (BCM). When testing for a short between high speed GMLAN (+) and (-) with the engine management module removed, a reading off 120 ohms is normal. However, to completely analyze the buss the BCM should be temporally removed when testing for shorts between the high speed GMLAN (+) and (-) while also making sure that all modules and the scan tool are disconnected from the buss. A normal reading across the high speed GMLAN buss with the terminating resistor at the DLC remove and all module and scan tool disconnected is infinite ohms. Make certain to reconnect the BCM after testing, it is necessary for proper vehicle powermoding.

From alldata

tech2

that's what my info say's too.


the fault is gone for now. clear all dtc in all modules with a scan tool. if something resets...address it then. keep it close to home for the first little while.


how long do you have you alldata subscription for? If not long, print off all the diagrams and info you can.

I must give you credit. You know you way around that car very well.

ricklovin93

i paid for a one year. Hooking up my scanner now. Thanks for all your help! hopefully one of the connectors were just dirty and they cleaned up when I unplugged them and plugged them back in. Fingers crossed! I want to check the power and ground for the power steering module. She keeps throwing out the three same codes. Could have a dirty ground.

ricklovin93

As my scanner was connecting to the system the instrument panel reset, and flashed power steering, now the security light is on.
U2129 wont go away. Its being stored in the Instrument panel. "lost Communication with remote function actuation"

ricklovin93

excuse the double (now triple posts) But since I never received a keyless entry remote, and since the car recognizes that the remote is not in the area, could that be setting off the security light? and possibly lead to my issues?

tech2

most gm products use the remote control door lock receiver for fob functions. I can't see the fob being the problem. I will have to read the dtc test procedure.

the code set in the ipc but does your scanner say which module the ipc has lost communication with? does the scan tool show and code descriptors....a 2 number code after the dtc ie u2129 05


what model year is this car?

RobbieDobbie29

Did you guys ever find a fix? I have a 07 SS/SC doing the same thing.

tech2

check and report back with the voltages of the can bus + and - lines at the dlc connector. if a line is shorted to grd it will bring down the entire bus.
finding the short involves disconnecting the bus lines in the middle and seeing which side shows continuity to grd. You then work your way down the line.

If you have the dtc, post it.