6E–262
ENGINE DRIVEABILITY AND EMISSIONS
Symptom Diagnosis
Preliminary Checks
Before using this section, perform the “On-Board
Diagnostic (OBD) System Check” and verify all of the
following items:
D
The powertrain control module (PCM) and malfunction
indicator lamp (MIL) (Service Engine Soon lamp) are
operating correctly.
D
There are no DTC(s) stored.
D
Tech 2 data is within normal operating range. Refer to
Typical Scan Data Values.
D
Verify the customer complaint and locate the correct
symptom in the table of contents. Perform the
procedure included in the symptom chart.
Visual/Physical Check
Several of the symptom procedures call for a careful
visual/physical check. This can lead to correcting a
problem without further checks and can save valuable
time.
This check should include the following items:
D
PCM grounds for cleanliness, tightness and proper
location.
D
Vacuum hoses for splits, kinks, and proper
connections, as shown on the “Vehicle Emission
Control Information” label. Check thoroughly for any
type of leak or restriction.
D
Air intake ducts for collapsed or damaged areas.
D
Air leaks at throttle body mounting area, mass air flow
(MAF) sensor and intake manifold sealing surfaces.
D
Ignition wires for cracking, hardness, and carbon
tracking.
D
Wiring for proper connections, pinches and cuts.
Intermittents
IMPORTANT:
An intermittent problem may or may not
turn on the malfunction indicator lamp (MIL) or store a
DTC. DO NOT use the Diagnostic Trouble Code (DTC)
charts for intermittent problems. The fault must be
present to locate the problem.
Most intermittent problems are caused by faulty electrical
connections or wiring. Perform a careful visual/physical
check for the following conditions:
D
Poor mating of the connector halves or a terminal not
fully seated in the connector (backed out).
D
Improperly formed or damaged terminal.
D
All connector terminals in the problem circuit should be
carefully checked for proper contact tension.
D
Poor terminal-to-wire connection. This requires
removing the terminal from the connector body to
check.
Road test the vehicle with a J 39200 Digital Multimeter
connected to a suspected circuit. An abnormal voltage
when the malfunction occurs is a good indication that
there is a fault in the circuit being monitored.
Use Tech 2 to help detect intermittent conditions. Tech 2s
have several features that can be used to locate an
intermittent condition. Use the following feature to find
intermittent faults:
D
Using Tech 2’s “Freeze Frame” buffer or “Failure
Records” buffer can aid in locating an intermittent
condition. Review and record the information in the
freeze frame or failure record associated with the
intermittent DTC being diagnosed. The vehicle can be
driven within the conditions that were present when the
DTC originally set.
To check for loss of diagnostic code memory, disconnect
the MAP sensor and idle the engine until the MIL (Service
Engine Soon lamp) comes on. DTC P0107 should be
stored and kept in memory when the ignition is turned
“OFF.” If not, the PCM is faulty. When this test is
completed, make sure that you clear the DTC P0107 from
memory.
An intermittent MIL (Service Engine Soon lamp) with no
stored DTC may be caused by the following:
D
Ignition coil shorted to ground and arcing at ignition
wires or plugs.
D
MIL (Service Engine Soon lamp) wire to PCM shorted
to ground.
D
Poor PCM grounds. Refer to the PCM wiring
diagrams.
Check for improper installation of electrical options such
as lights, cellular phones, etc. Route ignition coil wiring
away from the ignition coils. Check all wires from the
PCM to the ignition coil for poor connections.
Check for an open diode across the A/C compressor
clutch and check for other open diodes (refer to wiring
diagrams in
Electrical Diagnosis).
If problem has not been found, refer to
PCM Connector
Symptom tables.