I’m encountering a frustrating issue with my 1998 GMC Suburban and its OBD2 port. My INNOVA scanner, which works perfectly on my 1996 Silverado, 1997 Acura, and even newer 2017 VW Golfs, fails to connect to the Suburban. To isolate the problem, I’ve swapped the computer (PCM) between the Suburban and the Silverado. Interestingly, the Suburban’s PCM communicates with the scanner when installed in the Silverado. However, the Silverado’s computer also fails to connect when placed in the Suburban. This suggests the issue lies within the Suburban itself, not necessarily the PCM.
Following the GM Repair manual for troubleshooting, I’m focusing on potential communication faults. The manual references “CKT 800, no commo on the UART Data Line” and “CKT 1870 No Commo on Class-2 Data Line” as possible causes. I’m assuming the wiring diagrams and troubleshooting steps are consistent between 1997 and 1999 models, as I’m currently using manuals for those years while awaiting the 1999 specific documentation.
The first step in the manual states: “If the Powertrain Control Module (PCM) is not accessible with a scan tool, check for an open in Purple (PPL) (1807) wire.” I performed this test and confirmed connectivity between the Data Link Connector (DLC) pin 2 and the PCM’s #3 connector at its C8 pin out. This purple wire appears to be intact.
OBD2 Scanner Connection Issue in 1998 GMC Suburban
Moving through the other circuit tests – checking grounds, connectivity, voltages, and resistance at specified pin outs and components – I discovered an anomaly. There’s excessive voltage present on both the purple wire (2.4 VDC) at connector 2 (top row, second from the left) and the tan wire (4.5 VDC) at connector 9 (bottom row, 1st one on the left) of the DLC. The manual indicates “Greater than 1 VDC = repair the wire.” For comparison, I ran the same tests on the Silverado, and all voltage readings were below 1VDC, as expected.
This raises two key questions: What is the source of this ‘extra’ voltage in the Suburban’s DLC? And what does “BPMV” stand for, as mentioned in relation to a splice for the purple wire located “on the ‘Engine Harness approx. 13 cm into [the] BPMV Breakout.”? Is “BPMV” related to the braking system, perhaps “Break Pressure Modulator Valve”?
Data Link Connector Voltage Readings on 1998 GMC Suburban
I will continue to investigate the wiring diagrams and troubleshooting checklists in the repair manuals to pinpoint the source of the excess voltage and understand the role of the BPMV in this circuit. Hopefully, the detailed troubleshooting steps will lead to a solution for this OBD2 communication problem on my 1998 GMC Suburban.
