Analyzing Methods

ANALYZING DATA
Once the road test is completed, the results need to be analyzed to find and correct the exact fault that caused the symptom.

INSIGHTS FROM THE RECORDER
The use of the recorder greatly enhances the view of the Powertrain Control Module (PCM) operation when the fault occurs and allows for a systems approach to the problem. By setting the FUNCTION switch to PLAYBACK mode and inspecting the recorded channels, you can begin to evaluate the results.

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 fairly stable. Signals such as the Throttle Position (TP), Mass Air Flow (MAF), and engine rpm changing abruptly during a steady cruise are clues to correcting the problem.

Look for agreement in related signals. For example, if the TP signal changes during gentle acceleration, a corresponding change should occur in MAF, rpm, and ignition timing signals.

Make sure that signals act in proper sequence. An increase in rpm after the TP signal is increased is expected. However, if the rpm increases without a TP signal change, then a problem may exist.

ANALYZING METHODS
Use any of the following methods to further diagnose a suspected PCM signal or device. Some methods pertain to a certain type of PCM device. Follow the given strategy listed for each type of PCM signal listed in EEC-IV Monitor Measurement Methods.

- Change condition to cause response by input.

- Change input and verify output response.

- Click testing (solenoids/relays).

- Coil resistance (solenoids/relays).

- PCM input/output check.

- Harness continuity.

- Harness shorts.

- Output state check (solenoids/relays).

- Wiggle testing (DCV or OHMS).