3: Accumulating PCM Data

Powertrain Control Module (PCM) data can be accumulated in a number of ways. Gather as much data as possible when the malfunction is occurring to prevent misdiagnosis. Data should be accumulated during different operating conditions and based on the customer description of the intermittent fault. Reference the known good data values located in the Diagnostic Reference Value Charts.

This will require recording data in four conditions for comparison:
1. Key On Engine Off (KOEO)
2. HOT IDLE
3. 30 MPH
4. 55 MPH

Acquisition of PCM PID data using a scan tool is one of the easiest ways to gather information.

NOTE: Listed below are instructions for gathering PID data using a New Generation Star (NGS) scan tool.

Selecting and Viewing PIDs

NGS Main Menu:

1. Select Vehicle and Engine Selection and enter the proper year, vehicle and engine package from the menu.
2. Select DIAGNOSTIC DATA LINK.
3. Select POWERTRAIN CONTROL MODULE (PCM).
4. Select PID/DATA MONITOR AND RECORD.

NGS PID Menu:

5. Select the PIDs from the intermittent symptom chart or the PCM Pinpoint test. The star symbol next to each PID on the screen indicates that PID has been selected.
6. Turn ignition key ON or start vehicle.
7. Select the START key and access the PIDs.

Storing PIDs
1. When ready to capture and store the selected PIDs, press the trigger button.
2. Press trigger again when ready to save information.
3. The information is now located in the main recording area. Store to a viewing area before starting another recording or the data will be overwritten.

Recording Measurements Along with PIDs
1. Select DIGITAL MEASUREMENT SYSTEM.
2. Select one of the meters (i.e., VOLT METER).
3. Select LINK.
4. Select PID/DATA MONITOR.
5. Select PCM.
6. Select the PIDs and START to record.
7. Press REC to save DVOM function and PID data.
8. Press TRIGGER to save, store and view.

Playback of Stored PIDs
Look for abnormal behavior 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 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 TP is changed during acceleration, a corresponding change should occur in IAC, RPM and SPARK ADV PIDs.

Make sure the signals act in proper sequence. An increase in RPM after the TP is increased is expected. However, if RPM increases without a TP change, then a problem may exist.
1. Select VIEW RECORDER AREAS.
2. Select a viewing area.
3. Select up to four PIDs to review in the table format or two PIDs to review in the graph mode.

Possible Fault - Table Format:

4. Table Format: Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in the values. (Reference the EEC-V Charts and Graphs). Notice the major jump in the TP voltage while scrolling through the information. This example would require a smooth and progressive throttle pedal travel during a key ON and engine OFF mode.

Possible Fault - Graph Format:

5. 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. (Reference the EEC-V Charts and Graphs) This example would require a smooth and progressive throttle pedal with the key on and the engine off.

Peripheral Inputs
Some signals may require certain peripherals or auxiliary tools to aid in diagnostics. In some cases, these devices can be inserted into the measurement jacks of the scan tool or DVOM. The NGS is capable of recording the value from the measurement jacks on the NGS while storing the value from other PIDs. For example, connecting an electronic fuel pressure gauge to monitor and record the fuel pressure voltage reading, and capturing the data, would help find the fault. Listed are two types of peripheral devices available.
- Multi-Point Auxiliary Adapter - A/C, Fuel Pump (Rotunda 007-00023 or equivalent)
- Electronic Fuel Pressure/Vacuum Adapter - Fuel Pressure, Vacuum (Rotunda 007-00022 or equivalent)