When your car throws a fit with multiple warning lights and systems malfunctioning, it’s enough to make any driver’s heart sink. For auto technicians, these kinds of cases are both challenging and rewarding. Recently, a 2017 Chevy Equinox rolled into the shop with a host of electrical gremlins – no power steering, a barrage of instrument panel lights, and ominous messages like “AWD Problem” and “Service Steering System” flashing on the display. The initial visual inspection didn’t reveal much, but armed with a trusty OBD2 scanner, the diagnostic journey began to uncover a fascinating communication breakdown within the vehicle’s network. While the original technician utilized a Verus Edge, the principles of diagnosing such issues remain consistent regardless of the specific scan tool—whether it’s a high-end professional model or a reliable 2016 Equinox OBD2 scanner accessible to many enthusiasts and professionals alike.
Initial Inspection and OBD2 Scanner Insights
The 2017 Chevy Equinox in question was a salvage vehicle, pieced back together after a significant collision. This history immediately raised a red flag, suggesting potential wiring or component damage from the accident. A preliminary walk-around, however, didn’t expose any glaringly obvious issues. Given the electrical symptoms, the next logical step was to connect an OBD2 scanner to delve deeper into the car’s computer systems. Using a scan tool, similar in function to a 2016 Equinox OBD2 scanner in terms of reading diagnostic trouble codes, revealed two key CAN communication fault codes stored in the Body Control Module (BCM): U0121 (Loss of Communication with Electronic Brake Control Module) and U1814 (Powertrain Wake Up Circuit Fault). The U1814 code, further specified with a subtype 02, indicated a short-to-ground condition, pointing towards a potential electrical fault in the wake-up circuit.
CAN Network Analysis and Wake-Up Circuit Suspicions
CAN communication codes often signal network disruptions, and the first step in such cases is to assess which modules are actively communicating. A scan of the network revealed a limited number of modules online – PCM, TCM, BCM, Antitheft, and SRS. Crucially, several key modules were offline, including the PSCM (Power Steering Control Module), ABS (Anti-lock Brake System), AWD module, and TPMS (Tire Pressure Monitoring System). This confirmed a significant communication issue within the vehicle’s CAN network, and the U1814 code became the primary focus. Research into the Equinox’s communication architecture indicated that the BCM is responsible for sending a 12V wake-up signal to these offline modules. The DTC logic for U1814 suggested that the BCM would intentionally withhold this wake-up signal when the fault code is active, making it a prime suspect in the communication breakdown.
Tracing the Short to Ground
To investigate the U1814 short-to-ground fault, a basic electrical circuit approach was adopted. The BCM relies on a communication signal from the PCM when the ignition is turned on. The fault code suggested that the BCM was detecting a short to ground on this circuit. To test this, the connector at the BCM was disconnected, and a PowerProbe was used to check for a path to ground on the circuit. A path to ground was indeed detected. However, this initial finding wasn’t conclusive, as it could simply be a ground path through other connected modules. A resistance test was then performed to quantify the ground path. The expectation was that a significant short to ground would present very low resistance. The multimeter reading showed 1k Ohm resistance. While lower than typical communication circuit resistance, it wasn’t definitively a hard short. Nevertheless, the investigation proceeded with the assumption of a potential short, or a module dragging the voltage down.
Module Isolation and Resistance Testing
To pinpoint the source of the potential short or low resistance, a process of module isolation was initiated. According to the wiring diagrams, the modules on the wake-up circuit included the Fuel Pump Control Module, ABS Module, PCM, and Transmission Control Module. Each of these modules was systematically disconnected, one at a time, while monitoring the resistance reading. As each module was disconnected, the 1k Ohm resistance reading remained consistent until all listed modules were unplugged. Upon disconnecting the final module in the wake-up circuit, the resistance reading jumped to infinite. This crucial observation indicated that the fault was not in the wiring itself, but rather within one of the modules connected to the wake-up circuit. Since disconnecting all external modules resulted in infinite resistance, and the resistance stayed at 1k Ohm even with all external modules disconnected, the BCM itself became the prime suspect. It appeared that the BCM was internally shorted to ground on the wake-up sense circuit.
BCM Bypass Confirmation
To definitively confirm the BCM as the culprit, a bypass test was performed. The idea was to manually supply voltage to the wake-up circuit, bypassing the BCM’s control, to see if the offline modules would come back online. A test light connected to battery positive was used to send voltage to the wake-up circuit. As the vehicle was started with this bypass in place, all previously offline modules sprang back to life, restoring communication and resolving the initial symptoms. This conclusive test confirmed the diagnosis: the BCM was indeed faulty and failing to properly send the wake-up signal due to an internal short.
Conclusion: The Power of Systematic Diagnostics and OBD2 Scanners
This case highlights the effectiveness of a systematic approach to diagnosing complex automotive electrical issues. Starting with a basic visual inspection and then leveraging the capabilities of an OBD2 scanner, whether a professional-grade tool or a 2016 Equinox OBD2 scanner, is crucial for pinpointing the root cause of malfunctions. In this instance, the OBD2 scanner provided the initial fault codes that guided the diagnostic process. The U1814 code and the subsequent CAN network scan were instrumental in focusing the investigation on the BCM and the wake-up circuit. By combining scan tool data with logical circuit analysis and component isolation techniques, the faulty BCM was identified, leading to a successful resolution. For technicians and car enthusiasts alike, understanding CAN communication and utilizing OBD2 scanners are invaluable skills in modern automotive diagnostics.
