Yesterday during a long drive back from Michigan I got the service charging system message on the DIC. No issues for the rest of the trip the voltmeter look to be about 14.5 and while running an errand today the same message came up. Anyone have any input on what I should be looking for as a possible issue? The battery was new last summer and I'm thinking it might be the alternator about to go. Any input or suggestions would be appreciated thanks!!

RJ

Suburban Chicago

 

GM had a service bulletin that warned of aftermarket spark plugs causing this:

Service Charging System Message on DIC and DTC P0621

Models:
2005-2008 Chevrolet Corvette
2004-2008 XLR and XLR-V Series

This PI was superceded to add information about aftermarket spark plugs.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

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

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.

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.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.


Diagnostic Procedure for the code:

DTC P0621: Generator L-Terminal Circuit
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
DTC P0621 is a C Type DTC.

Conditions for Clearing the DTC
DTC P0621 is a C Type 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. Refer to system schematic to confirm if the vehicle being serviced uses the sense circuit as part of the charging system.

Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the generator.
2. Ignition OFF, test for B+ between the generator sense circuit terminal D and ground.
⇒ If less than the specified range, test the generator sense circuit for a short to ground, an open/high resistance.
3. Ignition ON, test for less than 1 volt between the generator turn on signal terminal B and ground.
⇒ If greater than the specified range, test the generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
4. Engine running, test for greater than 3.5 V between the generator turn on signal and ground.
⇒ If less than the specified range, test the generator turn on signal circuit for a short to ground, an open/high resistance. If the circuit tests normal, replace the ECM.
5. If the circuit tests normal, replace the generator.

Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• Generator Replacement
• Control Module References for ECM replacement, setup, and programming


If you have aftermarket plugs, this may be of help.

 

Is your horn working? They share a common fuse, and when my horn shorted out, i would get this message. It would blow the fuse. I ended up replacing the horns. don't buy the ones at the auto parts store. I put those in first and they sounded terrible. My wife would laugh at my car. I bought them from Gene Culley, and they sounded like a Vette should.

 

I had the same problem with my 05 coupe the battery was new an still service charging system so I replaced the alternator with a billet tech alternator an never had that problem again even with after market spark plugs.

 

I tried the horn and sure enough it didn't work!! Fuse blown, replaced and my issue is resolved!! Thanks everyone for the input!!

RJ

 

Awesome!

 

Good call Stephen. In fact, outstanding!!!

 

Thanks