Volvo VNL Service Manual page 46

Group 30 Electrical System—VNL, VNM
Battery Charging and Jump Starting
Do not connect battery charging or jump starting cables
to any part of an engine electronic system. This can
damage sensitive electrical devices. It is preferable not
to jump start vehicles which are electronically controlled.
The electronic control units can be damaged by voltage
spikes and current surges created by jump starting. When
charging batteries, always disconnect the battery cables
and charge each battery separately. This will prevent
the voltage coming into the battery from damaging other
system circuits.
Welding
CAUTION
Welding on trucks can damage the vehicle electrical
system/components due to the voltage and current
spikes that normally occur when welding. It is prefer-
able to avoid welding on an assembled truck, but if
any structure on or in contact with the vehicle must be
welded, follow the recommendations below:
•
Before welding on the vehicle, disconnect power to
the component being welded.
•
Disconnect both the positive (+) and negative (-)
battery cables. Disconnect the negative cable first.
Reconnect the positive cable first.
•
Disconnect engine/starter ground from the chassis.
Disconnect the power harness and vehicle interface
harness at the engine Electronic Control Unit (ECU).
•
If vehicles are equipped with systems with their own
Electronic Control Units (ECUs), such as Anti-lock
Brake or some transmission systems, disconnect the
system ECU.
•
Disconnect the electrical connectors at the rear of the
instrument cluster.
•
Attach the welder ground cable as close to the weld
as possible (no more than 2 feet from the part being
welded).
•
Do not connect the welder ground cable to the engine
ECU or the ECU cooling plate.
WARNING
Do not weld on the engine or engine components.
Welding on the engine or components mounted on the
engine can cause serious damage to the engine ECU.
44
Preventing Electrostatic Discharge
(ESD)
Anti-static wrist strap and mat
CAUTION
A wrist grounding strap must be worn when working
on electronic equipment such as the instrument cluster.
This is to prevent electrostatic discharge (ESD), which
can damage electronic components. To use the wrist
strap in a vehicle, attach the alligator clip to the nearest
electrical ground such as a metal mounting screw, a
ground terminal or preferably a ground stud.
CAUTION
Make sure the workbench has an anti-static mat which
is grounded to the nearest electrical outlet when work-
ing on electronic equipment such as the instrument
cluster. When working at an anti-static workbench, al-
ways keep the wrist strap connected to the anti-static
mat. This is to prevent electrostatic discharge (ESD),
which can damage electronic components.
Human skin can hold more than 1000 volts of static
electricity. Although getting a static shock is annoying, it is
not dangerous because there is so little energy stored by
clothing. But when dealing with circuits designed to sense
differences smaller than 1 volt, electrostatic discharge
can be a subtle but destructive problem. Circuit boards
mounted in the instrument cluster or in modules mounted
elsewhere may not fail immediately after being hit with
a static discharge. Rather they may work for a while,
then fail for no apparent reason. The culprit then is often
the normal warming up and cooling down process of the
module, engine or cab interior.
Grounding straps and anti-static mats are available for
minimal cost from electronic supply stores. Grounding
straps consist of a wrist strap, a coiled extension wire
and an alligator clip. Be sure to purchase one with a long
enough extension wire to allow free movement.
An anti-static wrist strap is available from Kent-Moore
(see Tools section of this manual). Call 1-800-328-
6657.
An anti-static mat is available from Newark (see Tools
section of this manual). Call 1–910–292–7240.
Service Procedures