Car Repair Advice by Professional Automotive Experts
Your Car "Service
Engine Soon" Illuminates While Driving You
Have Trouble Code The Main Engine/Transmission management
system (PCM - Powertrain Control
Module) is what controls your car
engine, transmission and emissions
systems. The PCM is a small
dedicated computer loaded with a
operating program. The "Service
Engine Soon" is illuminated when
the PCM has detected a malfunction
in the monitoring system. A computer
scanner can read trouble codes to
inform you on the particular system
that has failed. The oxygen sensor
(02 sensor) is a maintenance
item and should be replaced every
60,000 to 90,000 miles and can cause a "service engine soon"
light. After scanning your vehicle you
will receive a trouble code that
will indicate the sensor or system
that is out of operation range. Additional conditions can effect the
sensor or system that needs to be
considered.
Example:1
If scanning indicates a
MAS (Mass Air Flow) problem. Inspect
the intake boot or PCV Valve for
cracks or tears. Losing vacuum
between the throttle body and the
mass air flow can cause a false
reading.
Example:2 If
scanning indicates a EVAP
(Evaporative Emissions) system
failure. Inspect gas cap to be
fastened properly. Your PCM
pressure tests the fuel vapor system
in your car and can tell you there is a leak in the system, just
not where, so check the obvious,
check the remainder of the EVAP
system from there.
How to Use a ODB II Code Reader
Scanner "Check Engine" light warning
(This service can be performed by a novice on most vehicles)
If you see a "check engine" or a "service
engine soon" light in your instrument
cluster; your car has stored a diagnostic
trouble code. This means the computer system
on your vehicle has detected a problem with
the various systems it controls. Your car or
truck has many different sensors that
monitor the various vehicle systems. If the
trouble code light has been illuminated your
vehicle enters into "limp mode" this means
it is running on a predetermined program
that causes less efficient mileage and increased
emissions. A engine trouble coder reader is
an easy to use communication tool. All 1996
vehicles and newer utilize a "D" style plug
in connector that connects to the code
reader. Most vehicles connector is located
at the drivers compartment. Once the code
reader is plugged in you can retrieve
trouble codes the engine computer has stored
has in its memory. These codes are the same
codes the dealer and repair shops use to
replace sensors and clear codes.
1. Malfunction Indicator Lamp
The MIL has illuminated during driving this means there is a malfunction trouble code stored in the vehicles computer.
2. Locate Your Vehicles Computer Connector
Locate your vehicles computer connector (ALDL) most vehicles are on the drivers side lower. Some vehicles you might need to look
around a little, on the passengers side, and around the center console under a plastic cover.
3. Connecting to The Computer to Read Codes
Connect your code reader to the under
dash connector. The code reader will
automatically turn on and prompt you to the
next step for code retrieval. Once the code
has been identified look up the
identification on the trouble code chart
supplied with your code reader. After repair
has been made clear trouble codes and
recheck system. After codes have been
cleared the computer system is ready for
internal testing, this means that while the
car or truck is operation the onboard
computer is performing tests. These test are
called "monitors" most cars have between 4
and 8 monitor systems. The computer goes
though it testing procedure in about 40 to
60 miles.
Common Problems
1. After a car repair has been
performed the MIL indicator will illuminate
because the technician neglected to plug in
a sensor.
2. A blown fuse can cause the MIL to
illuminate.
3. A shorted sensor can cause the MIL to
illuminate.
Basic Tests 1.
Testing for DTS's
(Diagnostic Trouble Codes)for
this you need a PCM Scanner
this is a small hand held
electronic device that plugs
in to your cars OB2 (OBD11)
diagnostic connector (under
dash on left side, mostly).
This device can tell you the
trouble code that was stored
in your cars Main PCM.
(Power Train Control
Module).
Trouble Code Chart
2.
Testing fuel pressure
test to
see if you have the right
fuel pressure test with
gauge on fuel rail, most FI
(Fuel Injected) cars run
between 35 and 65 psi. If no
or little fuel pressure the
fuel pump maybe suspect.
3. Check
for vacuum leaks, listen for
obvious leaks.
Inspect air intake boot for
tears, this will fool the MAF (Mass Air Flow) sensor
into thinking the engine air
intake value is less than
what it is. Or a IAC (Idle
Air Control) bypass hose can
develop tears/holes in the
middle of the hose so
inspect thoroughly.
4. Check
for plugged exhaust system.
Excessive back pressure can
cause exhaust not to flow
causing engines to surge and
buck and lose power. Most
exhaust systems need to be
replaced between 60,000 and
120,000 miles.
5. Test for
weak ignition spark,
remove spark plug wire. Insert an extra spark plug into end of wire, attach
spark plug to ground then crank engine. You should observe blue spark between
spark plug gap. If a yellow spark is observed, your ignition coil is weak and
needs to be replaced. If your spark is not consistent you may need a ignition
module
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