Intermittent Diagnostic Techniques

INTERMITTENT DIAGNOSTIC TECHNIQUES

Intermittent diagnostic techniques help find and isolate the root cause of intermittent faults associated with the EEC system. The information is organized to help find the fault and perform the repair. The process of finding and isolating an intermittent starts with re-creating a fault symptom, accumulating PCM data and comparing that data to typical values, then analyzing the results. Before proceeding, be sure that:
- Customary mechanical system tests and inspections do not reveal a concern. (Remember, mechanical component conditions can make a PCM system react abnormally.)
- Service Bulletins, if available, are reviewed.
- Quick test and associated pinpoint tests have been completed without finding a fault, and the symptom is still present.

Re-creating The Fault

Re-creating the fault is the first step in isolating the cause of the intermittent symptom. A thorough investigation should start with a review of the customer concern on the work order, if necessary talk to the service advisor or contact the customer to obtain more details about the concern. If freeze frame data is available, it may help in re-creating the conditions at the time of a MIL DTC. Listed below are some of the conditions for re-creating the fault:

CONDITIONS TO RE-CREATE FAULT

Conditions For Re-Create Fault:

Accumulating PCM Data

PCM data can be accumulated in a number of ways. This includes circuit measurements with a multimeter or IDS or equivalent tester PID data. Acquisition of PCM

PID data using the IDS or equivalent tester is one of the easiest ways to gather information. Gather as much data as possible when the fault is occurring to prevent improper diagnosis. Data should be accumulated during different operating conditions and based on the customer description of the intermittent fault. Compare this data with the known good data values. See POWERTRAIN CONTROL MODULE (PCM) INSPECTION. Powertrain Control Module (PCM) Inspection

This will require recording data in four conditions for comparison: 1) KOEO, 2) HOT IDLE, 3) 48 km/h (30 mph) and 4) 89 km/ h (55 mph).

Analyzing Data From Playback Of Stored PIDs

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 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 RD. 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 fault may exist.

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. See POWERTRAIN CONTROL MODULE (PCM) INSPECTION. The charts apply to different vehicle applications (i.e., model, engine, transmission, etc.). Powertrain Control Module (PCM) Inspection