A car fails smog due to incomplete monitors and a "no communication" DTC. What should a technician do FIRST when diagnosing the issue?

When a car fails a smog check due to incomplete monitors and a "no communication" diagnostic trouble code (DTC), the first step in diagnosis should involve examining the communication between the vehicle's onboard diagnostics (OBD) system and the scan tool. Specifically, inspecting Pin 4 and Pin 5 for ground and Pin 16 for power is crucial because these pins are part of the OBD-II connector, which is integral for proper communication.

Pin 4 (Chassis Ground) and Pin 5 (Signal Ground) are essential for establishing a common ground for the communication, and issues with grounding can lead to the "no communication" DTC. Pin 16 provides battery power to the OBD-II system. If there is a problem with power or ground at these pins, the vehicle's computer system may not send or receive data appropriately, resulting in both the failure of the smog test due to incomplete monitors and the communication error.

Beginning diagnostics by checking these connections allows the technician to quickly identify whether a fundamental electrical issue exists that can be resolved, making it a logical first step before moving on to other tests or repairs. Other options, while potentially relevant later in the troubleshooting process, would not address the underlying communication issue as directly or