An OBD2 scanner retrieves Diagnostic Trouble Codes (DTCs) stored in the Powertrain Control Module (PCM). While it doesn’t directly control car components, understanding how the starting system works alongside the PCM can help pinpoint why a car won’t crank. The PCM controls components like the Fuel Pump Relay and Fuel Gauge. When the ignition switch is turned to the “Run” position, the PCM energizes the Fuel Pump Relay for about three seconds. This primes the fuel system for starting. The PCM requires power for both the Fuel Pump Relay and Fuel Gauge to function correctly.
Turning the ignition to “Crank” sends battery power (+12V DC) through the Starter Fuse to the Neutral Safety Switch (automatic transmissions) or Clutch Safety Switch (manual transmissions). A closed safety switch allows power to flow to the Starter Solenoid Relay coil. If the vehicle has an anti-theft system, the anti-theft module controls the ground for this relay. When the Starter Solenoid Relay is energized, it sends power to the Starter Solenoid coil, which in turn engages the starter motor.
A non-engaging starter motor might indicate issues outside the PCM’s direct control. Check for clean and tight battery connections, as high resistance can prevent the starter from drawing sufficient current. Worn Starter Solenoid contacts are another potential cause of starting problems. While an OBD2 scanner may not directly identify these issues, it can provide clues by revealing related DTCs stored in the PCM. For example, codes related to the crankshaft position sensor or immobilizer system can indirectly point towards starting problems.
