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 the TP, MAF and RPM that change abruptly when the vehicle is traveling at a constant speed are clues to a possible fault area.

Look for agreement in related signals. For example, if the APP1, APP2 and APP3 are changed during acceleration, a corresponding change should occur in TP1, TP2, LOAD, RPM and MAF V PIDs.

Make sure the signals act in proper sequence. An increase in RPM after the TP1 and TP2 are increased is expected. However, if RPM increases without a TP1 and TP2 change, then a fault may exist.

Table Format (Figure 2): Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in the values. (Refer to the following TP 1 example). Notice the major jump in the TP 1 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.

Graph Format: Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in the linear lines showing the transformation of values to the line graph. This example requires smooth progressive accelerator pedal pressure with the key ON and the engine OFF.

Fig 1: Scan Tool Display - PID Data

Courtesy of FORD MOTOR CO.