DTC P0621 Generator L-Terminal Circuit. GMC Truck Sonoma Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2000 🢒 Sonoma Pickup - 2WD 🢒 Engine 🢒 Engine Controls - 2.2L (L43) 🢒 DTC P0621 Generator L-Terminal Circuit

Circuit Description

The L-terminal circuit from the generator is a discrete circuit that has no splices and only one source and destination into the PCM. The PCM applies a voltage to the generator L-terminal circuit. A small amount of current flows from this circuit through the generator windings to ground to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L-terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.

The PCM expects to detect low voltage on the L-terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to have voltage potential when the generator is operational. When the PCM detects a fault, circuit shorted to ground, or circuit shorted to voltage.

Conditions for Running the DTC

The ignition switch in the ON position or the engine is operating.

Conditions for Setting the DTC

•	The PCM detects the L terminal as Active with the key ON and the engine not running or the PCM detects the L-terminal as Inactive with the engine running.

•	All conditions met for 6 seconds.

Action Taken When the DTC Sets

•	The PCM stores the DTC information into memory when the diagnostic runs and fails.

•	The malfunction indicator lamp (MIL) will not illuminate.

•	The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

•	A message is displayed on the Drivers Information Center.

Conditions for Clearing the DTC

•	A last test failed, or current DTC, clears when the diagnostic runs and does not fail.

•	A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.

•	Use a scan tool in order to clear the DTC.

Diagnostic Aids

Important:

•	Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the module. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM.

•	For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit prevents damage to the harness/component terminals.

•

Use a scan tool in order to diagnosis the generator circuits. The scan tool should display Inactive for the L terminal when the ignition is ON and the engine OFF, if not test the circuit for short to ground. When the engine is operating, the display should indicate that the L terminal is Active, if not test the circuit for an open.

•	A generator fault, such as a shorted output diode, malfunctioning regulator, open or shorted rotor, battery feed may cause a low battery charge.

DTC P0621 Generator L Terminal

Step	Action	Values	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Important: The following tests assumes that the generator belt is installed correctly and in good condition. The battery is adequately charged. Install a scan tool. Turn ON the ignition leaving the engine OFF. Monitor the DTC Information using a scan tool. Did P0621 set?	--	Go to Step 3	Testing for Intermittent Conditions and Poor Connections
3	Start the engine. Monitor the DTC Information using a scan tool. Did DTC P0621 fail this ignition?	--	Go to Step 4	Go to Diagnostic Aids
4	Turn OFF the engine. Disconnect the generator harness connector. Turn ON the Ignition with the engine OFF. Measure the voltage at the harness connector generator L - terminal and ground. Does the voltage measure equal to or greater than the specified value?	4.5 V	Go to Step 6	Go to Step 5
5	Turn OFF the ignition. Disconnect the PCM connector. Test the continuity of the L terminal circuit from the PCM harness connector to the generator harness connector with the DMM. Does the DMM indicate continuity within the specified range?	0-2ohms	Go to Step 7	Go to Step 8
6	Inspect for poor connections at the generator electrical connector. Refer to Connector Repairs in Wiring Systems. If you find a poor connection, repair the connection as necessary. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 12	Go to Step 9
7	Inspect for a poor connection at the PCM harness connector. Refer to Connector Repairs in Wiring Systems. If you find a poor connection, repair the connection as necessary. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 12	Go to Step 10
8	Repair the open/high resistance in the generator L - Terminal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete?	--	Go to Step 12	--
9	Replace the generator. Refer to Generator Replacement in Engine Electrical. Is the action complete?	--	Go to Step 12	--
10	Important: Program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete?	--	Go to Step 12	--
11	Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool. Start the engine and idle at the normal operating temperature. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable. Does the scan tool indicate that this diagnostic ran and passed?	--	Go to Step 12	Go to Step 2
12	Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed?	--	Go to the applicable DTC table	System OK