The PCM is continually monitoring and communicating with the different electronic systems of the vehicle. It monitors input data from sensors and uses this data to command solenoids, relays, switches, and indicator lamps. When the incoming data is within range and the PCM and output devices are functioning properly, the vehicle operates as it should.
But when one or more of these three variables (inputs, PCM, outputs) is out of range, a driveability problem can occur. If a Diagnostic Trouble Code is stored, identifying the problem is relatively simple. For non-code conditions, however, diagnosis requires pinpointing where the cause lies.
The Tech 1 “Scan” tool makes the search easier. It allows you to see data and activity on electrical circuits as seen by the PCM.
This distinction is important to understand. If the PCM is not seeing data correctly, it may set a code even though nothing is actually wrong with engine operation. This is why the OBD check must be performed before beginning any diagnostics. The OBD verifies proper PCM diagnostics.
The Tech 1 accesses vehicle electronic information through the Diagnostic Link Connector (DLC). Through this capability, you can witness actual voltage signals on a particular circuit and compare them to what should be the normal signals for that circuit. The Tech 1 not only reads data, it can also send data to allow you to command various switches, solenoids, and relays “ON” and “OFF.” This two-way capability is what makes the Tech 1 “bidirectional.” When connected to the DLC, the Tech 1 allows you to:
• conduct tests to monitor input data
• retrieve diagnostic data or codes
• control output functions
