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Home >> Buick >> 2007 >> Lucerne CX >> Repair and Diagnosis >> External Pages >> Different car >> Section 201 (Battery, Charging System And Starting System) >> Diagnostic Information and Procedures >> DTC P0621 >> Diagnostic Aids

Diagnostic Aids

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

If DTC P0621 is intermittent on the V6 engine, the B+ cable from the generator might be getting voltage induced from the spark plug wires. Shielding the B+ cable around the area of the ignition module with nickel tape might correct the intermittent condition.

DTC P0621

Step Action Yes No
Schematic Reference: Engine Controls Schematics (LX9) for the 3.5L (LX9) engine or Engine Controls Schematics for the 3.9L (LZ9) engine
Connector End View Reference: Powertrain Control Module (PCM) Connector End Views for the 3.5L (LX9) engine, Engine Control Module (ECM) Connector End Views for the 3.9L (LZ9) engine or Power and Grounding Connector End Views
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2
  1. Install a scan tool.
  2. Start the engine.
  3. With a scan tool, monitor the DTC information for DTC P0621 in Engine Controls.
Does the scan tool indicate that DTC P0621 has passed?		 Go to Testing for Intermittent Conditions and Poor Connections Go to Step 3 
3 With a scan tool, monitor the DTC information for DTC P0621 and DTC P0622 in Engine Controls.
Does the scan tool indicate that DTC P0621 and DTC P0622 have failed?		 Go to Step 6  Go to Step 4 
4 Test the generator turn on signal circuit for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 8  Go to Step 5 
5 Inspect for poor connections at the harness connector of the powertrain control module (PCM)/engine control module (ECM). Refer to Connector Repairs .
Did you find and correct the condition?		 Go to Step 8  Go to Step 7 
6 Repair the high resistance or open in the battery positive voltage circuit of the generator. Refer to Wiring Repairs .
Did you complete the repair?		 Go to Step 8  -
7
IMPORTANT: The replacement PCM/ECM must be programmed.
Replace the PCM/ECM. Refer to Control Module References for replacement, setup and programming.Did you complete the replacement?		 Go to Step 8  -
8
  1. Review and record the scan tool Fail Records data.
  2. Use the scan tool in order to clear the DTC.
  3. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.
  4. Using the scan tool, observe the Specific DTC Information for DTC P0621 until the test runs.
Does the scan tool indicate that DTC P0621 failed this ignition?		 Go to Step 2  System OK
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