Customer had a service Airbag message and indicator. The scan tool is identifying two codes related to the Service air bag message. What GM calls the supplemental inflatable restraint system.
U0151 – has to do with lost communication between the instrument panel cluster and the SIR restraints control module. B0081-5A has to do with Passenger presence system having a plausibility failure. There are 2 Air Bag modules in the truck. 1. SDM (sensing and diagnosing module) 2. PPM (passenger presence module.). The SDM is the main brain and does all the work. The first code U0151 is a loss of communication with the SDM. The second code B0081-5A s a communication problem between the SDM and the PPM. There is likely an issue with the SDM since the scan tool cannot communicate with it from the OBD2 port and after reviewing the wiring schematic I suspect a wiring issue or a bad module. To verify I need to diagnose the SDM to see why it is not present on the network. Both the SDM and the PPM are located under the driver and passenger seats. At this point I will need to remove the front seats to diagnose further
I have the interior out and saw some areas that look questionable which I need to investigate highlighted them in yellow. Particularly there is a split in the harness in the entrance to the driver’s seat and the rear seat. I Circled it in one of the pictures.
All the electrical tests have come back fine. The Air bag system fuses are good. The module receives 12v full time power. The module is also receiving ignition power when the key is turned on. Neither is shorted to ground or open.
The data communication line is not open or short at the harness. There is a clear communication signal pattern present at the module with it disconnected. The signal is also clean upstream at the Data link splice.
I pulled the SAS module, and bench tested it to see if it would generate a comm signal and it does not. At this point, based on the diagnostic test results, it appears the SDM module has failed and needs to be replaced. I’ve ordered a new one and will follow up after it’s installed.
With the new SDM module on order I opened the old module to see why it stopped working and discovered the driver component failed.
A new module was installed, and we used GM factory software to program the calibration based on the VIN, then used the Scan tool to set up the new module configuration and paired the Key with the BCM. With the new SDM module visible on the CAN both the IPC and PPS modules were able to communicate with it. The Service Air Bag Message was no longer displayed on the dash and the previous codes went away but the air bag indicator light was still present.
Though the original problem was fixed we needed to find out why the airbag indicator light was on. The system was rescanned and two new codes came up now that the new SDM is online.
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B0087-00 “Left Rear Side Impact Sensor”
B1019-00 “Sensing and Diagnostic Module (SDM) System
Configuration Error”
These codes are related to each other and identify a problem with the left rear side impact sensor. I will conduct further inspection for wiring issues. The failed sensor was preexisting but not visible because the old SDM module was not online. The new module setup failed to complete and generated trouble codes for the rear left impact sensor, however all other loops were enabled and learned.
The 2 new DTCs were Supplemental Inflatable Restraint (SIR) B0087-00 Left Rear Side Impact; Supplemental Inflatable Restraint (SIR) B1019-00 Sensing And Diagnostic Module (SDM) System Configuration Error
Circuit testing identified issues, I found a previous wiring repair in flexible conduit between the door and the body where the solder had failed creating a cold contact and repaired it. The repaired wire was the primary sensing wire for the side impact sensor. Further investigation required me to remove the rear seat and interior trim to inspect a harness connector which checked out fine and inspection of the harness continued down the line to SDM X2. A Scope was used to analyze the signal and ground side of the circuit with the connector attached to the SDM but no signal was present
The circuit was tested with the X2 disconnected from the SDM and the circuit proved fine with no short to ground or power and no opens. Further inspection of the X2 connector revealed pin 28 used for the ground side of the sensor circuit was damaged and had poor connection. A repair was made to the connector and the signal was restored. however, the Side impact sensor was not responding and needed to be replaced.
Ordered a new side impact sensor and installed it. All modules are green, and no service messages or indicator lamps are present.
That’s a diagnosis and repair.
