Service Charging System Message on DIC and DTC P0621

Models: 2005-2008 Chevrolet Corvette

2004-2008 XLR and XLR-V Series

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This PI was superceded to add information about aftermarket spark plugs. Please discard PIC4536A.

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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Some customers may comment that the Service Charging System message displays on the DIC. Using the Tech2, DTC P0621 is stored. This may be a result of aftermarket spark plugs or an open in circuit number 2540.

Recommendation/Instructions:
1. Check for aftermarket spark plugs. Plugs that are designed with a "Pulse" technology may interfere with this circuit and cause the Service Charging System message to illuminate on the IP and/or P0621 DTC store in the ECM. If aftermarket plugs are installed, replace plugs with OEM parts. This is not considered a warranty repair and all cost associated with this repair will be the customers responsibility.

2. Circuit 2540 is supplied voltage from the Horn fuse, position #2 in the UBEC. Apply the horn to see if it works. If the horn does not work, suspect an open fuse. This fuse may open if the horn is shorted due to water intrusion. If the horn is functional, check the integrity of circuit 2540 between the UBEC and the generator. Refer to SI document 1481125 for the schematic. Repair circuit 2540 as needed and re-evaluate the customers concern.


DTC Descriptor
DTC P0621: Generator L-Terminal Circuit


Diagnostic Fault Information
Circuit
Short to Ground
Open/High Resistance
Short to Voltage
Signal Performance

Generator Turn ON Signal
P0621
P0621
P0621
P0621


Circuit/System Description
The engine control module (ECM) uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the ECM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn on signal circuit. The ECM should detect low voltage on generator turn on signal circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect high voltage on the generator turn on signal circuit. The ECM performs Ignition ON and RUN tests to determine the status of the generator turn on signal circuit.

Conditions for Running the DTC
Ignition ON Test
• No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.

• The ignition is in RUN position.

• The engine is not running.

Run Test
• No generator, CKP sensors, CMP sensor DTCs are set.

• The engine is running.

Conditions for Setting the DTC
• During the Ignition ON test, the ECM detects high voltage on the generator turn on signal circuit for 5 seconds.

• During the RUN test, the ECM detects low voltage on the generator turn on signal circuit for 15 seconds.

Action Taken When the DTC Sets
• The ECM will command the charge indicator and or warning message to be illuminated on the instrument panel cluster (IPC) and the driver information center (DIC), if equipped.

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

• The ECM will store conditions, which were present when the DTC set as Failure Records data only.

Conditions for Clearing the DTC
• The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• Using the scan tool Clear DTC Information function can clear the DTC.

Diagnostic Aids
On vehicles equipped with a sense circuit connected to the voltage regulator.This circuit must have voltage for the charging system to operate properly.This circuit is used as a reference to control system voltage. All circuits must be tested at the generator before replacing any components.