Diagnosis of the Glow Plug System

Figure 3 - Glow Plug Thermal Switch:

SYSTEM CHECK


CAUTION: To prevent possible personal personal injury from a moving vehicle or operating engine do the following before performing the checks:
1. Engage the parking brake and block the wheels.
2. Place the automatic transmission in park or the manual transmission in neutral.

1. Release the two latches holding the passenger seat to the floor and lift the seat for access to the engine.

2. Disconnect the thermal switch connector (figure 3).

Figure 4 - Glow Plugs Installed:

3. Connect one end of an unpowered test lamp to the tip of a glow plug and the other end to ground (figure 4).
4. Turn the engine control switch to ON. Do not crank the engine.

5. The indicator lamp should come on for 2.5 to 4.5 seconds. The test lamp should light for 15 to 21 seconds. If either of the above fails to occur, check battery voltage and circuit wiring. Then refer to "Component Inspection."

Figure 5 - Fusible Link:

COMPONENT INSPECTION

FUSIBLE LINK
1. Disconnect the fusible link between the starter and the glow plug relay located in the left frame rail slightly forward from the starter
2. Check for continuity with an ohmmeter (figure 5).

Figure 6 - Glow Plug Relay:

GLOW PLUG RELAY
1. For relay location and removal, refer to "Glow Plug Relay Replacement."
2. Mark the relay and the two single prong connectors before disconnecting them to help identify the connections for reinstallation (figure 6).
3. Disconnect the three connectors.
4. Connect an ohmmeter to relay terminals A and B (figure 6).
5. At an ambient temperature of 20~C (68~F), the resistance should measure 13.5 ohms. If not, replace the relay.
GLOW PLUGS
1. Disconnect the negative battery cable and the connector to the bus bar
2. Loosen the nuts on the glow plugs and remove the bus bar.

Figure 7 - Testing A Glow Plug:

3. Connect one end of an unpowered test lamp to the battery connection at the starter
4. Reconnect the negative battery cable.
5. Touch the other end of the test lamp to the tip of each glow plug. The lamp should light. If not, either the plug needs to be replaced or it is not grounding properly
6. To check a plug, remove it from the engine. Check the threads for dirt or corrosion. Connect one lead of an ohmmeter to the tip of the plug and the other lead to the threads (figure 7). The resistance reading must be 0.


7. To replace a plug, refer to "Glow Plug Replacement."

Figure 8 - Glow Plug Timer:

GLOW PLUG TIMER
1. The timer is located under the instrument panel behind the heater hose. Lift out the heater hose. Remove the two screws holding the timer to the back of the bracket.
2. Disconnect the thermal switch connector
3. Backprobe terminals 5 and 6 with an unpowered test lamp (figure 8).
4. Turn the engine control switch to ON. The lamp should remain off for 15 to 21 seconds and then should turn on. If not, replace the timer Refer to "Glow Plug Timer Replacement."

Figure 9 - Thermal Switch:

THERMAL SWITCH
1. Remove the thermal switch (figure 9). Refer to "Thermal Switch Replacement."
2. Check the switch with an ohmmeter. In an ambient temperature above 0~C (32~F), the switch should be closed, and the resistance reading 0. Below 0~C (32~F), the switch should be open and the resistance reading 1.0 or infinite. If not, replace the switch.