Dodge RAM TRUCK 1500 1995 Service Manual page 1193

GENERAL DIAGNOSIS—DIESEL ENGINE 14 -111
UPPER PART OF
INTAKE MANIFOLD J9414-105
Fig. 30 intake Manifold Air Heater
BATTERY
(LEFT SIDE)
Fig. 31 Intake Manifold Air Heater Relays
The PCM provides a ground path for the intake
manifold air heater relays. The ground path is pro­
vided if intake manifold air temperature is 15°C
(59°F) when the ignition key is initially placed in the
ON position. When the ground is provided, the air
heater is energized to start the preheat cycle.
The preheat-cycle can be tested with a voltmeter or
test light. If the intake manifold air temperature is
above 15°C (59°F), the wait-to-start warning lamp
will not illuminate and the air heater will not be en­
ergized.
(1) With the engine not running and ambient air
temperature below 15°C (59°F), turn the ignition key
to the ON position.
(2) The wait-to-start warning lamp will come on
and the air heater relays should click ON signaling
the start of the preheat cycle. If the engine starter
is engaged before the preheat cycle of the heat­
ers is complete, the PCM will stop the remain­
ing preheat cycle.
(3) Check for battery voltage at both air heater ter­
minals (Fig. 30). The heater will only be ener­
gized for 10 to 30 seconds. Refer to the following
Air Heater Cycle Chart for a time/temperature com­
parison.
AIR HEATER CYCLE CHART
mmmmmcm
mmmmim
P K W A T C Y O E I I M E
« N m 0 N 0 H , M O N E
N O T R I M N N G
POST-HOT CYOE-
Above 15° C
(59° F)
0 seconds
No
-10°Cto 15° C
(15° F to 59° F)
10 seconds Yes
-18° C
to
-10° F
( 0 ° F t o l 5 ° F)
15 seconds Yes
Below-18° C
(0° F)
30 seconds Yes
J9414-133
HEATER TEST
(1) Disconnect both negative battery cables at both
batteries.
(2) Lift the rubber shields from each of the cable
connectors at the intake manifold air heater (Fig. 30)
to expose the cable terminals. Do not disconnect ca­
ble nuts.
(3) Use an ohmmeter to test the resistance be­
tween the cable terminal (not the mounting stud)
and a ground. The resistance should be zero (0). If
not, inspect for corroded or dirty cable connections.
Clean or repair the connections and retest before re­
placing heater. Also check both ends of the ground