Error Code P063B is defined as Generator Voltage Sense Circuit Range/Performance. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. This includes vehicle models from, but not limited to, Chrysler, Cummins, Dodge, Jeep, Land Rover, Mazda, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and power configuration.

Error Code P063B is associated with the generator voltage sense circuit. When the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) determines an improper signal within the generator voltage sense circuit code, then this code will be set.

The job of the generator voltage sense circuit is to oversee the voltage of both the alternator and battery during the vehicle’s operation. The output voltage of alternator must be a level capable of compensating for battery draws from electrical components including starter, lighting, and other accessories. Aside from that, the voltage regulator must change the output to provide the right amount of voltage to charge the battery.

Error Code P063B is set when the PCM sees an out-of-range situation, or a performance problem within the generator (alternator) sense circuit.

Other Generator Voltage Sense Circuit related codes include:

Common Symptoms

As with most codes, this code registers to the memory system and activates the Check Engine light. Other symptoms usually include:

  • Engine no start condition
  • Engine cranks slower than normal
  • Battery Warning light activated

Possible Causes

There are multiple reasons behind this code, some of the most common causes are:

  • Defective alternator
  • Defective voltage regulator
  • Defective serpentine belt tensioner
  • Damaged or loose serpentine belt
  • Blown fuse or fuse-able link (if applicable)
  • Corroded or damaged battery cable
  • Corroded or damaged connector
  • Faulty wiring
  • Defective PCM
  • Defective battery

How to Check

The first thing that must be done to diagnose this code accurately is to check the TSB (technical service bulleting) for the specific vehicle year, model, and power plant. This usually points to the right direction of diagnosis.

Next is to check all the associated wirings and connectors; search for signs of damage such as burnt wires, burnt spots, and bare wires caused by rubbing or scarping. Connections and connectors must be checked as well; look for signs of damages on the pins, corrosion, and other security and connectivity issues. This process must include all wiring connectors, connections, to the alternator, battery, PCM, and voltage regulator.

Vehicles can differ in charging system configurations. Some may be more complex including relays, fuse-able links, and fuses in some circumstances. Thus, visual inspections must also include checking the conditions of the serpentine belt and belt tensioner. The belt must be tight, with a good amount of flexibility; the tensioner must be able to move freely and apply the right amount of pressure on the serpentine belt. Based on the configuration of the charging system, in most cases, damaged or defective voltage regulator must require an alternator replacement.

Advanced Steps

Advanced steps for diagnosis vary from one vehicle to another and may require specific advanced equipment and tools, such as a digital multi-meter, and specific technical references for the vehicle. Voltage requirements also vary based on the specific year and model of the vehicle.

Voltage Checks

Battery voltage should be around 12V, and the starter should have battery voltage with the ignition switch in the start position. The presence of voltage with the starter not engaging is a sign of a defective starter or starter solenoid. The lack of voltage means the ignition switch is faulty, or there’s a problem in the wiring.

If this process determines the absence of a power source or ground, then perform a continuity test to check the integrity of the wiring, ignition switch, and other components. Continuity test must be performed with the power removed from the circuit while reading for wiring and connections must be at 0 ohms of resistance, unless otherwise specified in the technical data of the vehicle. Resistance or no continuity means there’s a faulty wiring problem (open or short) and must be repaired or replaced.

How to Fix

Depending on the diagnosis, common repairs for this code include:

  • Replacement of alternator
  • Replacement of blown fuse or fuse-able link (if applicable)
  • Repair or replacement of wiring
  • Cleaning corrosion off connectors
  • Repair or replacement of battery cables or terminals
  • Replacement of the serpentine belt
  • Replacement of the serpentine belt tensioner
  • Replacement of battery
  • Re-flashing or replacement of PCM

The most common misdiagnosis in this code is replacing the alternator, battery, or PCM when the problem is on the wiring or another component.