put stage and the indicator lamp are actuated by the
ECM. The pre-heating time is calculated by the ECM
in line with the coolant temperature. The glow plug
output stage switches the current through the glow
plugs. The glow plug indicator lamp goes out after a
pre-glow period has elapsed. Component or cable fail-
ures in the pre-glow system are indicated by the glow
plug lamp and stored in the ECM.

Glow Output Stage

With the ignition key in the On position a signal is

transmitted from the ECM to the glow plug output
stager. If no data is exchanged with the ECM the
glow plug stage is terminated after two seconds. The
glow plug out put stage constantly signals the cur-
rent operating state (ON/OFF) and any system
faults. The following faults are recognized by the out
put stage and transmitted to the ECM:

• Open circuit in one or more of the glow plug

leads

• Short circuit in the glow plug circuit

• Out put stage fault or temperature related shut-

off

If a failure in the glow plug system occurs, the

glow plug indicator lamp will be illuminated only as
long as the fault is current. If the failure is no longer
present, the glow plug indicator lamp will be
switched off but a code will be stored in the ECM.

After Glow

Once the engine has started, the ECM determines

the after glow time depending on cooling tempera-
ture. During this time the glow plugs continue to be
actuated by the glow plug output stage. This results
in improved smooth running after a cold start and
improved warming up properties, elimination of blue

exhaust after a cold start up and a more stable cold
starting speed.

If no signal is received from the coolant tempera-

ture sensor the signal from the oil sensor is used as a
substitute.

SPECIAL TOOLS

GLOW PLUG

REMOVAL

(1) Disconnect the negative battery cable.
(2) Remove the engine cover.
(3) Use special tool #9286 pliers to unplug the

glow plug wiring harness connector(s) at the glow
plug.

(4) Remove the glow plug(s) (Fig. 1).

INSTALLATION

(1) Screw glow plug(s) into cylinder head and

tighten to 12 N·m (115 lbs. in) (Fig. 1).

(2) Connect the glow plug wiring harness connec-

tor(s)

(3) Install the engine cover.
(4) Connect negative battery cable.

GLOW PLUG RELAY

DESCRIPTION

The glow plug relay supplies battery voltage to the

glow plug through a timed cycle that is related to
coolant temperature. The glow plug relay is located
under the battery. The purpose of a glow plug system

GLOW PLUG PLIERS

IGNITION CONTROL

8I - 1

is to improve combustion for low emissions and to
achieve easy starting at low temperatures.

OPERATION

When the ignition key is turned to the ON posi-

tion, the glow plug output stage and pre-glow indica-
tor lamp are actuated by the ECM. The duration of
the signal depends on the coolant temperature. The
glow plug relay has processing that communicates
with the ECM. If no data exchange occurs at the trig-
gering stage, the preheating is switched off after 2
seconds.

Start glowing is initiated when the key is in the

start position. The glow plugs (R13–R17) continue to
be supplied with voltage. This makes it possible to
stabilize the cold starting speed. (After glowing is ini-
tiated when the starter reject speed is reached).

After the engine starts, the ECM determines the

afterglow period in line with coolant temperature. If
no signal is received from the coolant temperature
sensor, afterglow is maintained for thirty seconds.

The following aims are reached by the afterglow :
• Improvement in warming-up properties

• Prevention of white exhaust smoke after cold

start

• Stabilizing of the cold starting speed
The glow plug output stage constantly signals the

current operating state and faults. The following are
faults detected and transmitted to the ECM :

• Open circuit at one or several glow plugs

• Short circuit in the glow plug circuit

• Relay fault
If the Glow plug relay detects an open circuit at a

glow plug, it is stored and indicated only once the
engine is running by the preglow indicator lamp com-
ing on for about one minute and a fault is stored in
the ECM. If a short circuit, a glow plug output stage
faulty or a temperature related switching off of out-
put stages is detected, the fault is stored and indi-
cated immediately by the preglow indicator lamp
coming on. Once the fault is no longer current, the
indicator is immediately switched off, but the fault is
stored in the ECM. If the fault is constantly current,
the preglow indicator lamp remains on until the igni-
tion is switched off.

DIAGNOSIS AND TESTING - GLOW PLUG
RELAYS

Refer to the appropriate Diesel Powertrain Diagno-

sis Manual for information on diagnosing the glow
plug relays.

Fig. 1 GLOW PLUG (S)

1 - GLOW PLUG
2 - WIRING HARNESS CONNECTOR

3 - INTAKE MANIFOLD
4 - ENGINE COVER

8I - 2

IGNITION CONTROL

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