For a complete wiring diagram Refer to Section 8WWhen Monitored:With the ignition on and the Glow Plugs commanded on.Set Condition:The Glow Plug Control Module reports a power supply circuit fault to the ECM.Possible CausesINTERMITTENT DTC(F344) FUSED ASD RELAY OUTPUT 2 CIRCUIT OPEN OR HIGH RESISTANCE(A29) FUSED B+ CIRCUIT OPEN OR HIGH RESISTANCE(Z906) GROUND CIRCUIT OPEN OR HIGH RESISTANCEGLOW PLUG MODULEENGINE CONTROL MODULE (ECM)Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.(Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)1. DTC IS ACTIVEDiagnose and repair any system voltage or ASD Relay DTCs before continuing with this test.Ignition on, engine not running.With the scan tool, Clear DTCs in the Engine Control Module (ECM).With the scan tool, actuate the Glow Plugs.Monitor the scan tool for at least two minutes.With the scan tool, select View DTCs.Is the status Active for this DTC?YesGo To 2NoRefer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure.(Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)2. (F344) FUSED ASD RELAY OUTPUT 2 CIRCUIT OPEN OR HIGH RESISTANCE

Turn the ignition off.Disconnect the Glow Plug Module harness connector.Turn the ignition on.Using a 12 volt test light connected to ground, check the (F344) Fused ASD Relay Output 2 circuit in the Glow Plug Module harness connector.The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.Is the test light illuminated and bright?YesGo to 3NoRepair the (F344) Fused ASD Relay Output 2 circuit for an open circuit or high resistance.Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - STANDARD PROCEDURE)3. (Z906) GROUND CIRCUIT OPEN OR HIGH RESISTANCE

Turn the ignition off.Using a 12 volt test light connected to B+, check the (Z906) Ground circuit in the Glow Plug Module harness connector.The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.Is the test light illuminated and bright?YesGo to 4NoRepair the (Z906) Ground circuit for an open circuit or high resistance.Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - STANDARD PROCEDURE)4. (A29) FUSED B+ CIRCUIT OPEN OR HIGH RESISTANCE

Using a 12 volt test light connected to ground, check the (A29) Fused B+ circuit in the Glow Plug Module harness connector.The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.Is the test light illuminated and bright?YesGo to 5NoRepair the (A29) Fused B+ circuit for an open circuit or high resistance.Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - STANDARD PROCEDURE)5. GLOW PLUG MODULEReplace the Glow Plug Module in accordance with the Service Information.Turn the ignition on.With the scan tool, Clear DTCs.With the scan tool, actuate the Glow Plugs.Monitor the scan tool for at least two minutes.With the scan tool, select View DTCs.Is the status Active for this DTC?YesGo to 6NoTest Complete.Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - STANDARD PROCEDURE)6. ENGINE CONTROL MODULE (ECM)Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Glow Plug Module and the Engine Control Module (ECM).Look for any chafed, pierced, pinched, or partially broken wires.Look for broken, bent, pushed out or corroded terminals.Refer to any Technical Service Bulletins that may apply.Were any problems found?YesRepair as necessary.Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoReplace the Engine Control Module (ECM) in accordance with the Service Information.Perform the ECM Verification Test Ver. 1. (Refer to 9 - ENGINE - STANDARD PROCEDURE)