Service manual

G424F(FE) Service Manual 233 Chapter 8. Basic Troubleshooting
Basic Troubleshooting
Intermittents
An intermittent fault is the most difficult to
troubleshoot since the MIL flashes on at random,
causing uncertainty in the number of flashes or the
conditions present at the time of the fault. Also, the
problem may or may not fully turn “ON” the MIL light
or store a code.
Therefore, the fault must be present or able to be
recreated in order to locate the problem. If a fault is
intermittent, use of diagnostic code charts may
result in the unnecessary replacement of good
components.
Corrective Action
Most intermittent problems are caused by faulty
electrical connections or wiring. Perform careful
visual/physical check for:
• Poor mating of the connector halves or terminal
not fully seated in the connector body (backed
out)
• Improperly formed or damaged terminal. All
connector terminals in problem circuit should be
carefully reformed or replaced to insure proper
contact tension
• Loose connections or broken wires
• Poor terminal to wire connection crimp
If a visual/physical check does not find the cause of
the problem, perform the following:
(1) Drive the vehicle with a voltmeter or “Service”
tool connected to a suspected circuit. Check if
circuit is active and signal is reasonable.
(2) Using the “Service” tool, monitor the input signal
to the SECM to help detect intermittent
conditions.
(3) An abnormal voltage, or “Service” reading, when
the problem occurs, indicates the problem may
be in that circuit.
(4) If the wiring and connectors check OK, and a
diagnostic code was stored for a circuit having a
sensor, check sensor.
An intermittent “Service Engine Soon” light with no
stored diagnostic code may be caused by:
• Ignition coil shortage to ground and arcing at
spark plug wires or plugs
• MIL light wire to ECM shorted to ground
• SECM grounds (refer to SECM wiring diagrams).
Check for improper installation of electrical options
such as lights, 2-way radios, accessories, etc.
EST wires should be routed away from spark plug
wires, distributor wires, distributor housing, coil and
generator. Wires from SECM to ignition should have
a good connection.