Analyzing PCM Data
Look for abnormal events or values that are clearly incorrect. Inspect the signals for abrupt or unexpected changes. For example, during a steady cruise most of the sensor values should be relatively stable. Sensors such as throttle position (TP), mass air flow (MAF), and RPM that change abruptly when the vehicle is traveling at a constant speed are clues to a possible concern area.
Look for agreement in related signals. For example, if TP changes during acceleration, corresponding changes should occur in idle air control (IAC), RPM, and SPARK ADV PID.
Make sure the signals act in correct sequence. An increase in RPM after the TP is increased is expected. However, if RPM increases without a TP change, then a fault may exist.
Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in values. (Refer to the following TP1 example). Service the major jump in the TP1 voltage while scrolling through the information. This example would require a smooth and progressive accelerator pedal travel during a key on and engine off mode.