A technician is diagnosing a vehicle that was towed into the shop with a “cranks, but won’t start” complaint. After verifying the symptom, he connects a scan tool to the DLC and turns the ignition...

A technician is diagnosing a vehicle that was towed into the shop with a “cranks, but won’t start” complaint. After verifying the symptom, he connects a scan tool to the DLC and turns the ignition switch on. The scan tool displays a “No communication” message. At that point, he disconnects the bus bar to isolate all the nodes on the data bus (star configuration). He then uses a jumper wire to connect just the PCM to the DLC. With the ignition switched on, the scan tool begins communicating with the PCM. What type of problem is indicated, and how can the technician isolate the problem?