Intermittent Symptoms

Intermittent diagnostic techniques help find and isolate the root cause of intermittent faults associated with the EEC system. This information is organized to help find the fault and perform the repair. There are examples that illustrate the diagnostic techniques. The process of finding and isolating an intermittent fault starts with recreating the fault symptom, accumulating Powertrain Control Module (PCM) data and comparing that data to typical values and analyzing the results.

Before proceeding, be sure that:
- Customary mechanical system tests and inspections do not reveal a problem. (Remember, mechanical component problems can make a PCM system react abnormally.)
- Technical Service Bulletins (TSBs) have been reviewed.
- Quick Test and associated pinpoint diagnosis have been completed without finding a fault, and the symptom is still occurring.

Recreating the Fault
Recreating the fault is the first step in isolating the cause of the intermittent symptom. If Freeze Frame Data is available, it may help in recreating the condition(s) at the time of a Malfunction Indicator Lamp Diagnostic Trouble Code (MIL DTC). Listed below are some of the conditions for recreating the fault:

Engine Type Conditions Non-Engine Type Conditions
Engine Temperature Ambient Temperature
Engine RPM Moisture conditions
Engine Load Road conditions
Engine idle/accel/decel (smooth-bumpy)

Accumulating PCM Data
Powertrain Control Module (PCM) data can be accumulated in a number of ways. Gather as much data as possible when the fault is occurring to prevent misdiagnosis. Data should be accumulated during different operating conditions, and based on the customer description of the intermittent fault. Refer to the known good data values located in the end of Diagnostic Reference Value Charts. This will require recording data in four conditions for comparison: 1) KOEO, 2) HOT IDLE, 3) 48 kph, 30 MPH and 4) 88 kph, 55 MPH. Acquisition of PCM 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) tester scan tool.

Selecting and Viewing PIDs
1. Key ON or start vehicle.







2. Select VEHICLE & ENGINE SELECTION and enter the proper year, vehicle and engine package from the menu.
3. Select DIAGNOSTIC DATA LINK.
4. Select POWERTRAIN CONTROL MODULE (PCM).







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. Select the START key and access the PIDs.

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 New Generation Star (NGS) Tester or Digital Volt Ohm Meter (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
- Electronic Fuel Pressure/Vacuum Adapter - Fuel Pressure, Vacuum

Analyzing PCM Data
Once the fault area is identified, the circuit must be checked to determine if the wiring or component is at fault. When making circuit and component measurements, make sure all accessories, as well as dome, trunk and hood lights are off. Use any of the following methods to diagnose a suspected PCM wire circuit or device. Some methods are specific to a certain type of PCM device.
- Click testing/output test mode (solenoids/relays)
- Coil resistance (solenoids/relays)
- Harness opens
- Harness shorts

Change Input and Verify Output Response
The purpose is to verify how the PCM and actuator circuit respond to sensor input.
1. Select, view and record the appropriate sensor PID(s).
2. Create a condition to cause input condition to change.
3. Observe change in actuator PID or actuator signal circuit measured by use of NGS.

Example:
- Increase Throttle Position (TP) under load, observe IAC PID and circuit change.

Click Testing (Solenoids/Relays)
The purpose is to activate a solenoid or relay from the PCM by entering Output Test Mode.
1. Key ON.
2. Enter Active Command Mode.
3. Turn outputs on and then off.
4. Listen for relays to click ON and OFF.

Examples:
- FP relay and cooling fan relays.