Accumulating PCM Data

Accumulating Powertrain Control Module (PCM) data can be done in a number of ways. Gather as much data as possible when the malfunction is occurring to prevent misdiagnosis. Data should be accumulated in different operating conditions and based on the customer description of the intermittent fault. This will require data recording in these four conditions for comparison: 1) Key On Engine Off (KOEO), 2) HOT IDLE, 3)30 MPH and 4)55 MPH. Acquisition of PCM Parameter Identification (PID) data using a scan tool is one of the easiest ways to gather information. 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. Information saved is now located in the main recording area. Save 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 a meter (i.e., VOLTMETER).
3. Select LINK and LINK MONITOR.
4. Select the PIDs and START recording.
5. Press REC to save DVOM function and PID data.

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 Accelerator Pedal (AP), Manifold Absolute Pressure (MAP) 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 AP position is changed during acceleration, a corresponding change should occur in RPM.

Make sure the signals act in proper sequence. An increase in RPM after the AP is increased is expected. However, if RPM increases without a AP 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.

AP Sensor Values:

4. Table Format: Scroll through the PID data while analyzing the information. Look for sudden drops or spikes in the values. (Refer to the AP example). Notice the major jump in the AP voltage while scrolling through the information.

TP Graph:

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. (Refer to the Throttle Position (TP) example.) This example only applies to an analog signal.

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

PID Values (Example):

Comparing PCM Data
After the PCM values have been acquired, it is necessary to determine the fault area. Typically, it will require the comparison of the actual values from the vehicle to the typical values. Refer to the pinpoint test procedures.