Jeep 1996 Grand Cherokee Service Manual page 470

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DESCRIPTION AND OPERATION (Continued)
ELECTROSTATIC DISCHARGE (ESD) SENSITIVE
DEVICES
All ESD sensitive components are solid state and a
symbol (Fig. 6) is used to indicate this. When han-
dling any component with this symbol comply with
the following procedures to reduce the possibility of
electrostatic charge build up on the body and inad-
vertent discharge into the component. If it is not
known whether the part is ESD sensitive, assume
that it is.
(1) Always touch a known good ground before han-
dling the part. This should be repeated while han-
dling the part and more frequently after sliding
across a seat, sitting down from a standing position,
or walking a distance.
(2) Avoid touching electrical terminals of the part,
unless instructed to do so by a written procedure.
(3) When using a voltmeter, be sure to connect the
ground lead first.
(4) Do not remove the part from its protective
packing until it is time to install the part.
(5) Before removing the part from its package,
ground the package to a known good ground on the
vehicle.
Fig. 6 Electrostatic Discharge Symbol
DIAGNOSIS AND TESTING
TROUBLESHOOTING TOOLS
When diagnosing a problem in an electrical circuit
there are several common tools necessary. These tools
are listed and explained below.
• Jumper Wire - This is a test wire used to con-
nect two points of a circuit. It can be used to bypass
an open in a circuit.
WARNING: NEVER USE A JUMPER WIRE ACROSS
A LOAD, SUCH AS A MOTOR, CONNECTED
BETWEEN A BATTERY FEED AND GROUND.
• Voltmeter - Used to check for voltage on a cir-
cuit. Always connect the black lead to a known good
ground and the red lead to the positive side of the
circuit.
8W - 01 GENERAL INFORMATION
CAUTION: Most of the electrical components used
in today's vehicle are solid state. When checking
voltages in these circuits use a meter with a 10-me-
gohm or greater impedance.
• Ohmmeter - Used to check the resistance
between two points of a circuit. Low or no resistance
in a circuit means good continuity.
CAUTION: - Most of the electrical components used
in today's vehicle are Solid State. When checking
resistance in these circuits use a meter with a
10-megohm or greater impedance. In addition, make
sure the power is disconnected from the circuit.
Circuits that are powered up by the vehicle electri-
cal system can cause damage to the equipment and
provide false readings.
• Probing Tools - These tools are used for probing
terminals in connectors (Fig. 7). Select the proper
size tool from Special Tool Package 6807, and insert
it into the terminal being tested. Use the other end
of the tool to insert the meter probe.
Fig. 7 Probing Tool
INTERMITTENT AND POOR CONNECTIONS
Most intermittent electrical problems are caused
by faulty electrical connections or wiring. It is also
possible for a sticking component or relay to cause a
problem. Before condemning a component or wiring
assembly check the following items.
• Connectors are fully seated
• Spread terminals, or terminal push out
• Terminals in the wiring assembly are fully
seated into the connector/component and locked in
position
• Dirt or corrosion on the terminals. Any amount
of corrosion or dirt could cause an intermittent prob-
lem
• Damaged connector/component casing exposing
the item to dirt and moisture
• Wire insulation that has rubbed through causing
a short to ground
• Wiring broke inside of the insulation
8W - 01 - 5