If an intermittent problem is evident, follow the guidelines below.
Preliminary Checks
Before using this section, you should have already performed the Diagnostic
System Check - Engine Controls.
Perform a thorough visual inspection. This inspection can often lead to correcting
a problem without further checks and can save valuable time. Inspect for the following
conditions:
| • | Engine control module (ECM) grounds for being clean, tight, and in their
proper location |
| • | Vacuum hoses for splits, kinks, collapsing and proper connections as shown
on the vehicle emission control information label--Inspect thoroughly for any
type of leak or restriction. |
| • | Air leaks at the throttle body mounting area and the intake manifold sealing
surfaces |
| • | Ignition wires for cracks, hardness, proper routing, and carbon tracking |
| • | Wiring for proper connections |
| • | Wiring for pinches or cuts |
Diagnostic Trouble Code (DTC) Tables
Do not use the DTC tables to try to correct an intermittent fault. The fault
must be present to locate the problem.
Incorrect use of the DTC tables may result in the unnecessary replacement of
parts.
Faulty Electrical Connections or Wiring
Most intermittent problems are caused by faulty electrical connections or wiring.
Perform a careful inspection of suspect circuits for the following:
| • | Poor mating of the connector halves |
| • | Terminals not fully seated in the connector body |
| • | Improperly formed or damaged terminals--All connector terminals in
a problem circuit should be carefully inspected, reformed, or replaced to insure contact
tension. |
| • | Poor terminal-to-wire connection--This requires removing
the terminal from the connector body. |
Road Test
If a visual inspection does not find the cause of the problem, the vehicle can
be driven with a voltmeter or a scan tool connected to a suspected circuit. An abnormal
voltage or scan tool reading will indicate that the problem is in that circuit.
If there are no wiring or connector problems found and a DTC was stored for
a circuit having a sensor.
Fuel System
Some intermittent driveability problems can be attributed to poor fuel quality.
If a vehicle is occasionally running rough, stalling, or otherwise performing badly,
ask the customer about the following fuel buying habits:
| • | Do they always buy from the same source? If so, fuel quality problems
can usually be discounted. |
| • | Do they buy their fuel from whichever fuel station is advertising the
lowest price? If so, check the fuel tank for signs of debris, water, or other contamination. |
Use the following tables when diagnosing a symptom complaint:
