P063C Diagnostic Trouble Code: Generator Voltage Sense Circuit Low

Fault code P063C is called “Generator Voltage Sense Circuit Low” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P063C

The OBD-II fault code P063C is a generic fault code, which is defined as “low voltage alternator voltage measurement sensor circuit”. In this case, the error indicates the specific circuit with which the problem occurred.

P063C Diagnostic Trouble Code: Generator Voltage Sense Circuit Low

The alternator is designed to generate the current needed by the vehicle at a given time. This is accomplished by a circuit in the control module that estimates the total power consumption.

The alternator voltage measurement circuit is designed to monitor the alternator and battery voltage while the vehicle is running. The alternator output voltage must be at the proper level.

The alternator needs to compensate for the charge consumption of the battery and electrical components, including the starter, lights, and various accessories. In addition, the voltage regulator must deliver power output to provide enough voltage to charge the battery.

This fault in the vehicle is related to the alternator voltage sensing circuitry. When the powertrain control module (PCM) detects low voltage in the alternator voltage sensing circuit, code P063C will be set.

When the error occurs, the battery warning lamp may illuminate, and the engine check lamp, or both.

Symptoms of vehicle malfunctions

The main signal that an error P063C has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be recorded in the memory as a fault).
  2. The battery check lamp illuminates.
  3. Some gauges or sensors on the instrument panel may be inactive.
  4. The engine does not crank well on startup.
  5. Problems with starting the engine.

When error P063C appears, the engine may not start, so this code should be considered serious. Therefore, it is better to correct this error as soon as possible.

Factors that can cause this error code

The error code P063C can mean that one or more of the following problems have occurred:

  • Faulty alternator.
  • Faulty voltage regulator.
  • Open or short circuit in wiring harness.
  • Loose or damaged connectors.
  • Poor grounding is a common cause.
  • Blown fuse or fusible link.
  • Low charge level or fully discharged battery.
  • Loose or damaged timing belt.
  • Defective battery.
  • Sometimes faulty PCM or programming error is the cause.

How to fix or reset OBD-2 code P063C

Some suggested steps for troubleshooting and fix the error code P063C:

  1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P063C appeared.
  2. Clear the error codes from the computer memory and test-drive the vehicle to find out if the malfunction appears again.
  3. If the error code appears again, visually inspect the electrical wires and control module connector.
  4. Visually inspect and test the alternator.
  5. If necessary, repair or replace the alternator and any defective wires.
  6. Check the voltage regulator and battery pack.
  7. Pay attention to the timing belt.
  8. If there are no defects, check the PCM itself and its program part.

Diagnose and repair of problems

Other errors may sometimes be present when trouble code P063C occurs. Associated codes usually refer to abnormal system voltages. And also to performance range mismatch codes, which may refer to various sensors.

If there are no additional codes, the first thing to do is to check the battery to determine its state of charge and overall performance. If the battery is discharged or damaged, recharge or replace it.

Checking the wiring

After checking the battery, visually inspect all wiring associated with the alternator. If necessary, repair or replace to ensure effective load transfer.

If no visible signs of shorts or other damage are found, use a voltmeter to check the resistance and ground. Replace if necessary to ensure that all electrical values are within the limits specified by the manufacturer.

Also locate any fuses that are in any way connected to the charging system. After checking, replace any damaged or suspect fuses.

Testing the alternator

If all the wiring is checked, you need to test the alternator itself with a multimeter. In most cases, it is the faulty alternator that causes error P063C.

If the defect in the alternator is confirmed, replace it with a new or remanufactured alternator, as this is almost always more cost-effective than repairing it. However, make sure that the unit being replaced is identical to the original in all respects, including mounting brackets and specifications.

After replacement, start the engine and watch the indicator light on the dashboard to make sure the alternator is working properly. The warning light should go out within a few seconds.

If the charging lamp does not come on, it may be the cause of the error. Therefore, you need to test and troubleshoot the alternator check lamp.

You can also measure the system voltage, it should be between 14.2 and 14.8 volts. Allow the vehicle to run at least one full drive cycle before re-scanning the system. Most likely there will be no P063C error, but sometimes additional clearing with the scan tool is necessary.

On which vehicles does this problem occur most frequently

Fault code P063C can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chrysler
  • Dodge (RAM)
  • Jeep
  • Land Rover (Range Rover)
  • Mazda

Fault code P063C can sometimes be found with other errors. The most common are the following: P063A, P063B, P063D.


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