Actron GM Code Scanner CP9001 - Manual (Page 12)

12
Using Codes
Using Trouble Codes as Part of a Basic
Troubleshooting Procedure
A driveability problem can have many
possible causes which are not related
to the computer system. Reading
codes is one part of a good trouble-
shooting procedure consisting of:
1) Visual Inspection
2) Basic Mechanical Checks
3) Reading Codes
4) Using the Vehicle Service Manual
5) Erasing Codes
1) Visual Inspection
Doing a thorough visual and “hands-
on” underhood inspection before
starting any diagnostic procedure is
essential!
You can find the cause of many
drivability problems by just looking,
thereby saving yourself a lot of time.
• Are routine maintenance items
O.K.?
– Clean air filter
– Correct fluid levels
– Recommended tire pressure
– Good ignition system components
- spark plugs, wires and the like.
• Has the vehicle been serviced
recently?
– Sometimes things get recon-
nected in the wrong place, or not
at all.
• Don’t take shortcuts.
– Inspect hoses and wiring which
may be difficult to see because of
location beneath air cleaner
housings, alternators and similar
components.
• Inspect all vacuum hoses for:
–Correct routing. (Hoses may be
missing or misconnected.) Refer
to vehicle service manual, or
Vehicle Emission Control
Information
(VECI)
decal
located in
the engine
compart-
ment.
–Pinches and kinks.
–Splits, cuts or breaks.
• Inspect wiring for:
–Contact
with sharp
edges.
(This
happens
often.)
–Contact
with hot
surfaces, such as exhaust
manifolds.
–Pinched, burned or chafed
insulation.
–Proper routing and connections.
• Check
electrical
connectors
for:
–Corrosion
on pins.
–Bent or
damaged pins.
–Contacts not properly seated in
housing.
–Bad wire crimps to terminals.
Problems with connectors are
common in the engine control system.
Inspect carefully. Note that some
connectors use a special grease on
the contacts to prevent corrosion. Do
not wipe off! Obtain extra grease, if
needed, from your vehicle dealer. It is
a special type for this purpose.
FRONT
OF CAR
U.S.A.
EM
G GAP
YST
CE BOOSTER
HVAC CRUISE
BRAKE BOOSTER
TO TRANS MODE
EGR
VAC
REG
EGR
VAC
REG
FUEL PRESS REG.