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1F – 364 ENGINE CONTROLS
Before Starting
Before using this section you should have performed the
On-Board Diagnostic (EOBD) System Check and deter-
mined that:
D The engine control
module (ECM) and the Malfunction Indicator Lamp
(MIL) are operating correctly.
D There are no Diagnostic Trouble Codes (DTCs)
stored.
D The scan tool data is within normal operating range.
Verify the customer complaint, and locate the correct
symptom in the table of contents. Check the items indi-
cated under that symptom.
Important: The problem may or may illuminate the Mal-
function Indicator Lamp (MIL) or store a Diagnostic
Trouble Code (DTC). Do not use the DTC tables for inter-
mittent problems. The fault must be present to locate the
problem.
Most intermittent problems are caused by faulty electri-
cal connections or wiring. Perform a careful visual/physi-
cal check. Check for the following conditions:
D Poor mating of the connector halves or a terminal not
fully seated in the connector.
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 re-
moving the terminal from the connector body to
check.
The vehicle may be driven with a Digital Voltmeter
(DVM) connected to the suspected circuit. An abnormal
voltage when a malfunction occurs is a good indication
that there is a fault in the circuit being monitored.
A scan tool can be used to help detect intermittent con-
ditions.
Using a scan tool's Freeze Frame buffer can aid in locat-
ing an intermittent condition. Review and record the in-
formation in the freeze frame associated with the
intermittent DTC being diagnosed. The vehicle can be
driven within the conditions that were present when the
DTC originally set.
SYMPTOM DIAGNOSIS
IMPORTANT PRELIMINARY CHECKS
INTERMITTENTS
Visual/Physical Check
Several of the symptom procedures call for a careful
visual/physical check. The importance of this step can-
not be stressed too strongly. It can lead to correcting a
problem without further checks and can save valuable
time. This check should include:
D ECM grounds for being clean, tight, and in their
proper location.
D Vacuum hoses for splits, kinks and proper connec-
tions. Check thoroughly for any type of leak or restric-
tion.
D Air leaks at throttle body mounting area and intake
manifold sealing surfaces.
Wiring for proper connections, pinches and cuts.
To check loss of DTC memory, disconnect the Throttle
Position (TP) sensor and idle the engine until the MIL
comes ON. DTC P0122 should be stored in memory
and kept in memory when ignition is turned OFF. If not,
the
ngine control
module (ECM) is faulty. When this test is completed,
make sure that you clear the DTC from memory.
An intermittent MIL 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 wire to ECM shorted to ground.
D Poor ECM grounds.
Check for an electrical system interference caused by a
defective relay, ECM driven solenoid, or switch.
They can caused a sharp electrical surge. Normally the
problem will occur when the faulty component is oper-
ated.
Check for improper installation of electrical options such
as lights, cellular phones, etc.
Check for open diode across the A/C compressor clutch
and check for other open diodes.
DAEWOO T-154 BL2,3
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