How to Bypass PCM Voltage Regulator Fix The Voltage Issue


Does the voltage regulator fail to control the voltage on your vehicle? Then,you can fix it if you know how to bypass PCM voltage regulator on an alternator.

A voltage regulator is a small built-in device on your vehicle. It controls the DC voltage from the battery and supplies the engine with the proper amount of energy.

But sometimes, if the voltage regulator fails, you will face several problems. In that case, bypassing the regulator is the best solution ever. However, some other options are also available.

Here, we will show you the symptoms of a bad voltage regulator and the process to fix the issue.

Few Common Symptoms of a Bad Voltage Regulator

Few Common Symptoms of a Bad Voltage Regulator

Before you go for the solution, make sure the voltage regulator fails. To be very confident, here we have listed out some bad voltage regulator symptoms.

If you face any of these mentioned below, then it’s your regulator that needs treatment. Here they are-

  • Clusters may fail to run correctly.
  • The dashboard light is dimming or continuously giving battery flashing.
  • Gauge is showing an inaccurate reading.
  • Sudden high voltage
  • Sudden low voltage in engine start
  • No voltage showing sometimes

After facing any of the symptoms mentioned above, you should check your voltage regulator once. Sometimes, there can be a fault in the gauge system.

However, if you have a 6.7 Cummins voltage regulator, this method can help also. But, if you are very sure of the bad voltage regulator, then skip this part and proceed with the solution.

How to Test Voltage Regulator?

How to Test Voltage Regulator

Testing the voltage regulator is quite easy. You only need a multimeter and the method of checking. If you don’t have the multimeter can get one like the AstroAI is much popular for ECM checking on vehicles. You can also hire one from any mechanical store.

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Step-1: Connect the Multimeter

Connect the multimeter with the engine battery. Attach the red wire of the multimeter to the positive(+) terminal of the battery. And the black one will go to the negative(-) terminal.

Switch on the power of the multimeter by turning the knob towards the Voltage(V) DC.

Step-2: Start the Engine

Now, start the engine.  There will be a voltage reading on the multimeter screen. Remember, it will show around 12.6  Volt.

Step-3: Increase the Engine Power

Increase the fuel power and set it idle from 1500 to 2000 Rpm. If you see the voltage is increasing with the increasing rpm, then the voltage regulator needs to repair or replace.

If the voltage does not exceed 12V instead starts decreasing, the battery can not provide a proper power supplement. Or there may be the alternator is not getting an adequate charge.

In this case, check all the terminals connecting the battery to the voltage regulator. If any connections are loosened or rusty, it can fail to supply the proper voltage.

If the voltage reading is still on 12.6V or around it, it indicates there is no problem with the OEM Voltage regulator. The problem can be –the battery or the gauge.

But if you still face any of the problems mentioned, install an external voltage regulator bypass the voltage regulator. It will solve the voltage issues entirely.

How to Bypass PCM Voltage Regulator?

How to Bypass PCM Voltage Regulator

Bypassing the PCM(Powertrain Control Module) can fix the issue of the voltage supplying problem. Let’s see how you can make your own alternator that will work as an external voltage regulator.

Things You Will Need

  • Aftermarket voltage regulator
  • Regulator plug harness
  • Wires for connecting

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Before going for the steps, let’s be clear that here you have to go through 2 phases-

  1. Setup the alternator regulator
  2. Connect the regulator

Phase-1: Setup the External Alternator VR

At first, let’s make your own alternator VR. Steps for it are-

Step-1: Connect the Harness with the Alternator

Two wires from the harness plug will go to the alternator.The blue wire might be written with (F) beside will go to the alternator. The white/green one will connect to the other side of the alternator plug. If your harness plug comes with 2 wires, then, no issue, connect and take out another wire from the blue wire.

The red wiregoes to the positive side of the battery. There might be written (A) beside the red wiring connection. Two wires of the harness plug can be blue and green, can be blue and white or even two black cables only. These colors may vary for different models, so no need to worry.

Pro Tip: Connect a fuse box with the red wire that goes with the battery. It helps to prevent any drainage when you switch off the engine.

Step-2: Tape The Wires

Tape the wires properly using any good tape to protectthem from any leakage or fuse. Mount the harness plug into the alternator voltage regulator.

Phase-2: Wireup the Alternator Regulator

Now, time to connect the alternator regulator to the battery and the ECM panel.

Step-1: Open the Engine Hood

Well, the first step is to open the frontengine hood. It’s the place where you will find the voltage regulator.

Make sure the engine is cold enough as you will be working with the wires, and if the vehicle engine is hot, you may burn your hands.

Pro Tips: If possible, use hand gloves while working to avoid any injuries.

Step-2: Disconnect the Battery Terminals

Disconnect the terminals from the battery. It will block all power sources from the battery to the voltage regulator.

Detach both the red and black wires meaning the positive and negative terminal.

Step-3: Find out the Voltage Regulator

Now find out the voltage regulator. You will find it mostly on the above there on any side. It will be near the voltage regulator attached tothe vehicle computer panel. Check there is a rectangular shaped socket. And there will be four wires connected. From there, the voltage regulator wire is coming out. You have to connect your alternator with this socket.

Step-4: Mount the External Alternator

Now connecting time starts.

Mount the alternator voltage regulator on the inner fender or on the firewall using bolt screws. Use one sheet metal screw for grounding.

Step-5: Connect the Wires to the Alternator Voltage Regulator

Connect the green wire coming out from the alternator to the bottom post to the voltage regulator. And the green wire goes to the top post of the voltage regulator. It is a 12V wire from a key switch of 12V.

You can cut out the factory wires that were connected before and isolate them with taping. You don’t need them anymore.

Step-6: Connect a Fuse Box to the Voltage Regulator Switch

To connect the fuse box, you have to find out the 12V key switch from the switch board panel’s back.Observe the switches carefully. You will see a switch reference written “Power Window” herewith.

Put a fuse and hook it up into the bottom slot of the switch box.

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Step-7: Connect the Wire with Battery

Now, connect the red wire to the battery’s positive side. And thegrounding wire coming out of the alternator regulator goes to any ports on the voltage regulator.

Your bypassing is completed. So, easy!

You only need vivid knowledge to find out the ports and wiring them up to make the alternator regulator. And then you can do it all by yourself.

Wrap Up

The context is a complete guide about how to bypass PCM voltage regulatoron an alternator. But if you need to make sure about your faulty regulator, you can check this too after reading it.

Here, we have shown the bypassing process and mentioned all the symptoms and regulator checking method.