Dodge RAM TRUCK 1500 1995 Service Manual page 441

8F • 2 AUDIO SYSTE1S
B R
and should be checked in the case of RFI or EMI
noise complaints include the following:
• radio antenna base ground
• engine-to-body ground strap
• resistor-type spark plugs
• radio suppression-type secondary ignition wiring.
In addition, if the source of RFI or EMI noise is
identified as a component on the vehicle (i.e.:genera-
tor, blower motor, etc.), the ground path for that com­
ponent should be checked. If excessive resistance is
found in that circuit, repair as required before con­
sidering any component replacement.
Fleet vehicles are available with an extra-cost RFI-
suppressed Powertrain Control Module (PCM). This
unit reduces interference generated by the PCM on
some radio frequencies used in two-way radio com­
munications. However, this unit will not resolve com­
plaints of RFI in the commercial AM or FM radio
frequency ranges.
D I A G N O S I S
RADIO
(1) Check fuses 7, 17 and 18 in fuseblock module
and fuses 1 and 2 in Power Distribution Center
(PDC). If OK, go to next step. If not OK, replace fuse.
(2) Check for battery voltage at fuses 1 and 2 in
PDC. If OK, go to next step. If not OK, repair feed
circuit from battery to PDC as required.
(3) Turn ignition switch to ON position. Check for
battery voltage at fuse 7 in fuseblock module. If OK,
go to next step. If not OK, repair circuit to ignition
switch as required.
(4) Turn ignition switch to OFF position. Discon­
nect battery negative cable. Remove instrument clus­
ter bezel. Remove radio, but do not unplug any
connections. Check for continuity between the radio
chassis and a good ground. There should be continu­
ity. If OK, go to next step. If not OK, repair radio
ground circuit as required.
(5) Connect battery negative cable. Turn ignition
switch to ON position. See Radio and Speaker Con­
nectors chart. Check for battery voltage at cavity 6 of
left (gray) radio connector. If OK, go to next step. If
not OK, repair circuit to fuse 7 as required.
(6) Turn ignition switch to OFF position. Check for
battery voltage at cavity 7 of left (gray) radio connec­
tor. If OK, replace radio. If not OK, repair circuit to
fuse 17 in fuseblock module as required.
SPEAKERS
(1) Turn radio on and adjust balance and fader
controls to check performance of each individual
speaker. Note the speaker locations that are not per­
forming correctly. Go to next step.
If vehicle has Infinity premium speaker package
and all speakers lack bass or low frequency re­
sponse, see Filter Choke/Speaker Relay diagnosis.
(2) Turn radio off. Disconnect battery negative ca­
ble. Remove instrument cluster bezel and remove ra­
dio. See Radio and Speaker Connector chart. Check
both the speaker feed and return cavities at radio for
continuity to a good ground. There should be no con­
tinuity. If OK, go to next step. If not OK, repair wir­
ing circuit as required.
(3) Check resistance between speaker feed and return
cavities. Meter should read between 3 and 8 ohms
(speaker impedance). If OK with Infinity speakers, go to
next step. If OK without Infinity speakers, see diagnosis
for Radio. If not OK, go to step 5.
(4) Install a known good radio. Connect battery nega­
tive cable. Turn on radio and test speaker operation. If
OK, see diagnosis for Radio. If not OK, disconnect battery
negative cable, remove test radio and go to next step.
(5) Unplug speaker wiring connector. Check for
continuity between speaker feed cavity at radio and
at speaker. Repeat check between speaker return
cavity at radio and at speaker. There should be con­
tinuity. If OK with Infinity speakers, go to next step.
If OK without Infinity speakers, replace speaker. If
not OK, repair wiring circuit as required.
(6) Check for continuity between cavity 1 of
speaker connector and a good ground. There should
be continuity. If OK, go to next step. If not OK, re­
pair wiring circuit to ground as required.
(7) Install radio. Connect battery negative cable. Turn
radio on. Check for battery voltage at cavity 4 of
speaker connector. If OK, replace speaker. If not OK, re­
pair circuit to filter choke/speaker relay as required.
FILTER CHOKE/SPEAKER RELAY
The radio filter choke/speaker relay is used to switch
power to the individual speaker amplifiers used with
the Infinity premium speaker package. The choke and
relay are serviced only as an assembly. If all speakers
operate, but have no bass or low frequency response,
the choke/relay is suspect. However, before replacement
make the following checks of the circuit:
(1) Check fuse 17 in fuseblock module. If OK, go to
next step. If not OK, replace fuse.
(2) Check for battery voltage at fuse 17 in fuse-
block module. If OK, go to next step. If not OK, re­
pair circuit to Power Distribution Center as required.
(3) Remove knee blocker and unplug choke/relay
connector. See Radio and Speaker Connectors chart.
Check for battery voltage at cavity 1 of choke/relay
connector. If OK, go to next step. If not OK, repair
circuit to fuse 17 as required.