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Glow Plug System Test

NOTE: If engine coolant temperature is above 86°F (30°C), disconnect wire from coolant temperature sensor for all tests. Unless otherwise noted, perform all tests with engine off.
  1. Turn ignition on. Check voltage between glow plug buss bar and engine block. If voltage is at least 10 volts for 1-6 seconds after ignition is turned on, go to step 9. If not, go to next step.
  2. Check for battery voltage on battery side of glow plug relay No. 1. If voltage exists, go to next step. If not, repair or replace circuit between battery and relay No. 1. Repeat step 1.
  3. Connect voltmeter between pin No. 1 of control module and ground. Turn ignition and read voltage. If voltage is at least 10 volts, go to next step. If not, replace ignition switch or repair circuit to control module. Repeat step 1.
  4. Turn ignition off. Check for continuity between glow plug relay No. 1 and buss bar. If continuity exists, go to next step. If not, repair or replace circuit as needed. Repeat step 1.
  5. With voltmeter connected between pin No. 2 of control module and ground, turn ignition on. If voltmeter reads at least 10 volts for 1-6 seconds after ignition is turned on, replace glow plug relay No. 1, then repeat step 1. If not, go to next step.
  6. Disconnect coolant temperature sensor and control module connector. Check for continuity between pin No. 13 of control module and ground. If continuity is indicated, repair short to ground in pin No. 13 circuit. If no continuity exists, go to next step.
  7. Reconnect control module connector (leave sensor disconnected). Connect voltmeter between pin No. 2 of control module and ground. Turn ignition on. Voltmeter should read at least 10 volts for 1-6 seconds after ignition is turned on. If not, replace control module and repeat step 1. If voltage is correct, go to next step.
  8. Remove coolant temperature sensor. Place sensor in 68°F (20°C) water. Check sensor resistance. If resistance is 2800-3800 ohms, repair circuit between pin No. 13 of control module and coolant temperature sensor. If not, replace sensor. After repairing circuit or replacing sensor, repeat step 1.
  9. Connect voltmeter between buss bar and ground. Turn ignition on. Voltage should be 5-8 volts for 6 seconds after glow plug relay No. 1 turns off. If reading is correct, go to step 14. If reading is incorrect, go to next step.
  10. Check for battery voltage at glow plug relay No. 2. If voltage exists, go to next step. If not, repair circuit between battery and relay No. 2. Repeat step 1.
  11. Turn ignition off and check for continuity between buss bar and glow plug relay No. 2. If continuity exists, go to step 13. If not, go to next step.
  12. Disconnect glow plug system dropping resistor from wiring harness. With ohmmeter multiply knob on "X1" setting, check continuity of resistor. If continuity exists, repair circuit as needed. If not, replace resistor and repeat step 1.
    CAUTION: Use care when handling resistor, as it becomes very hot during glow plug system testing.
    Fig 1: Glow Plug System Wiring Diagram
    G10522
  13. Connect voltmeter between pin No. 4 of control module and ground. Read voltage while cranking engine. If voltmeter indicates 10 volts or more for 7 seconds after cranking, replace glow plug relay No. 2 and repeat step 9. If it does not, replace control module and repeat step 1.
  14. Connect voltmeter between pin No. 4 of control module and ground. Read voltage while cranking engine. If meter reads 9 volts or more while cranking engine, go to step 16. If not, go to next step.
  15. Connect voltmeter between pin No. 3 of control module and ground. If voltmeter reads at least 9 volts while cranking engine, replace control module and repeat step 1. If not, replace ignition switch and/or repair wiring to pin No. 3 of module. Repeat step 1.
  16. Disconnect glow plug buss bar. Remove glow plugs and inspect for breaks, cracks or other damage. If plugs are okay, go to next step. If not, check engine compression and then go to next step.
  17. Measure resistance of each glow plug. Resistance should be no more than .23 ohms at 68°F (20°C). Replace plugs as needed. Install good and/or new plugs and buss bar. Repeat step 1. If plugs are okay, go to next step.
  18. With control module and engine harness connectors disconnected, check continuity between pin No. 7 of control module and pin No. 4 of engine harness connector (harness side). Also check continuity between pin No. 9 of control module and pin No. 4 of engine harness connector. If continuity exists in both circuits, leave engine harness disconnected and go to next step. If not, repair defective circuit(s) and repeat step 1.
  19. Check continuity between pin No. 4 of engine harness connector (engine side) and ground. If continuity exists, reconnect engine harness and go to next step. If not, repair circuit and repeat step 1.
  20. Attempt to start engine. If engine starts, turn ignition off and go to next step. If engine does not start, glow plug system is okay. Reconnect coolant temperature sensor. Go to ENGINE PERFORMANCE DIAGNOSIS  .
  21. Connect voltmeter between buss bar and ground. Start engine. Voltmeter should indicate 5-8 volts for 6-30 seconds. If so, problem is located outside of glow plug system. If no voltage is read after engine starts, turn engine off and go to next step. If voltage is correct, but lasts for more than 30 seconds, turn engine off and go to step 24.
  22. Connect voltmeter between pin No. 12 of control module and ground. Start engine. If voltage is about 14 volts, turn engine off and go to next step. If voltage is 12 volts or less, repair wiring between pin No. 12 and alternator. Repeat step 1.
  23. Connect voltmeter between pin No. 4 of control module and ground. Start engine. If voltmeter reads 10 or more volts for 6-30 seconds, repeat steps 9 through 13 as they were incorrectly performed. If reading is not as indicated, replace control module and repeat step 1.
  24. Connect voltmeter between buss bar and engine block. Reconnect coolant temperature sensor. Start engine and observe voltmeter while disconnecting sensor. If voltmeter reads 5-8 volts with sensor connected and zero voltage with sensor disconnected, problem is located outside of glow plug system. If not, repeat step 21.
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