Intermittent Problem Diagnosis

NOTE: An intermittent problem may or may not illuminate the MIL or set a DTC. Unless directed there from a specific test DO NOT use DTC testing for intermittent problems. Fault must be present to locate problem.

Most intermittent problems are caused by faulty electrical connections or wiring. Perform a careful visual/physical check for following conditions:

Perform the Diagnostic System Check. See appropriate SELF DIAGNOSTICS article.
Many intermittent open or shorted circuits come and go with harness or connector movement caused by vibration, engine torque, bumps or rough pavement.
Test for intermittents by performing the applicable procedure from the following list:
1. Move related connectors and wiring while monitoring the appropriate scan tool data.
2. Move the related connectors and wiring with the component commanded ON and OFF, with the scan tool. Observe the component operation.
3. With the engine running, move related connectors and wiring while monitoring engine operation.
Verify whether the harness or connector movement affects any of the following systems:
1. Data displayed.
2. Component or system operation.
3. Engine operation.
Repair the components as necessary.
Intermittents are usually caused by one or more of the following:
1. Poor electrical connections.
2. Terminal tension.
3. Wiring problems.
Carefully inspect the suspected circuit for the following conditions:
1. Poor mating of the connector halves.
2. Terminals backed out or not fully seated in the connector body.
3. Improperly formed or damaged terminals. Test for poor terminal tension.
4. Poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
5. Corrosion to water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation, with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits.
6. Wires that are broken inside the insulation.
7. Pinched, cut, or rubbed through wiring in the harness.
8. Wiring that is in contact with hot exhaust components.
9. Repair the condition as necessary.
Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test lamp or a DVOM may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See appropriate SYSTEM WIRING DIAGRAMS article.
Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component.
An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
The following data may help to diagnose this type of intermittent condition:
1. Freeze Frame/Failure Records
2. Scan Tool Snapshot
3. Vehicle Data Recorder
If the intermittent is relate to heat, review the following data:
1. High ambient temperatures.
2. Underhood or engine generated heat.
3. Circuit generated heat due to a poor connection, or high electrical load.
4. Higher than normal load conditions, such as towing.
If the intermittent is related to cold, review the following data:
1. Low ambient temperatures. In extremely low temperatures, ice may form a connection or component. Test for water intrusion.
2. The condition only occurs on a cold start.
3. The condition is not present after the vehicle warms up.
4. Information from the customer may help to determine if the trouble follows a pattern that is temperature related.
Some electrical components or circuits are sensitive to Electromagnetic Interference (EMI) or other types of electrical noise. Perform the following procedures:
1. Inspect for a misrouted harness that is too close to a high voltage or high current device. This condition may induce electrical noise on a circuit that could interfere with normal circuit operation. Inspect for wires that are too close to the secondary ignition components, motors, or the generator.
2. Determine whether the electrical system interference is caused by a malfunctioning relay, PCM driven solenoid or switch. These components may cause a sharp electrical surge. Normally, the condition will occur when the malfunctioning component is operating.
3. Determine whether non-factory or aftermarket add-on accessories are installed in the vehicle. These accessories may lead to an emission related OBD-II failure. Determine if any of the following non-factory or aftermarket add-on accessories is causing the intermittent:
  - Lights
  - 2-Way Radios
  - Amplifiers
  - Electric Motors
  - Remote Starters
  - Alarm Systems
  - Cell Phones
Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode.
Test for proper performance of the generator.
If a DTC is determined to be intermittent, and the tests in this section do not reveal a condition, refer to the Vehicle Data Recorder later in this procedure.
There are only a few situations when reprogramming a PCM is appropriate, such as the following:
1. A new service PCM is installed.
2. A PCM from another vehicle is installed.
3. Revised software or calibration files have been released for this vehicle.

CAUTION: DO NOT re-program the PCM with the same software or calibration files that are already present in the PCM. This is not an effective repair for any type of driveability problem.

Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software of calibration. See PROGRAMMING in appropriate SELF DIAGNOSTICS article.
If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
Freeze Frame/Failure Records, where applicable contains the conditions that were present when the DTC set. Perform the following:
1. Review and record Freeze Frame/Failure Records.
2. Clear the DTCs using the scan tool.
3. Turn the key to OFF and wait 15 seconds.
4. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records, as closely as possible. The vehicle must also be operating within the Conditions For Running DTC. See CONDITIONS FOR RUNNING DTC in the supporting text of the DTC being diagnosed in the appropriate SELF DIAGNOSTIC article.
5. Monitor DTC status for the DTC being tested. The scan tool will indicate RAN, when enabling conditions have been satisfies long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
An alternate method is to drive the vehicle with the DMM connected to a suspected circuit. An abnormal reading on the DMM when the conditions occurs, may help you locate the condition.
The scan tool can be set up to take a snapshot of the parameters available via serial data. The snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combination of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets.
An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further.
Refer to the scan tool user instructions for more information on the Snapshot function.
The Vehicle Data Recorder (J 42598) is connected to the Data Link Connector (DLC) and sent with the customer. The Vehicle Data Recorder (J 42598) captures data for later retrieval and analysis by the technician. Refer to the Vehicle Data Recorder user instructions for more information.