P0651 Code: Sensor Reference Voltage “B” Circuit / Open

Plugging in a scan tool into your vehicle’s OBD-II port allows you to view codes that have been set, which can help you figure out what’s wrong with it. If this is your first time encountering the P0651 fault code, you might wonder what it means and what are its possible causes. This guide will help you know more about this code.

What Does the P0651 Code Mean?

Diagnostic trouble code (DTC) P0651 stands for “Sensor Reference Voltage “B” Circuit/Open.” This code sets if the powertrain control module (PCM) detects a potential issue with its 5-volt reference signal.

The PCM sends out a five-volt reference signal to all applicable engine sensors. As the sensor resistance changes in response to varying pressure, temperature, or speed conditions, it sends the PCM an input voltage signal.

If the PCM discovers a potential problem with this reference signal or if it doesn’t receive an input signal from one of the engine sensors, it will set the P0651 code.

The P0651 fault code is typically accompanied by more specific sensor codes. However, if it’s stored alone, there might be a problem with the PCM’s programming.

The severity of the P0651 code depends on which circuit is having the open condition. To properly determine the severity of this code, one might need to check other trouble codes stored in the vehicle’s memory alongside this code.

Note: The definition of code P0651 might be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0651 Code?

Trouble codes can have several possible triggers. Here are some of the most common causes of the P0651 code:

• Open circuits or connectors
• Defective or blown fuses or fusible links
• Defective system power relay
• Faulty engine sensor 
• PCM failure
• Wiring issues

What are the Common Symptoms of the P0651 Code?

When you’re dealing with certain DTCs, you might notice several symptoms, but that’s not always the case. Some DTCs might not show any signs at all. As for the P0651, here are some of the most common signs you might notice:

• Illuminated malfunctioning indicator lamp or check engine light
• Engine might not start
• Vehicle stuck in “limp” mode
• Engine performance problems, such as rough running and misfiring
• Transmission might not shift properly
• Other powertrain malfunctions

How to Diagnose the P0651 Code

Different trouble codes can share the same symptoms, potential causes, and areas of concern, making DTC repair complicated. Before you make any repairs or replace parts, you need to perform a thorough diagnosis first. Doing so can help you avoid damaging your vehicle even further and racking up a hefty repair bill. If you’re not familiar with DTC troubleshooting, you will need the expertise of a professional.

If you want to know more about how diagnostic and repair procedures are conducted for the P0651 fault code, there are a lot of resources available today. Of all these resources, vehicle-specific repair manuals are your best choice. That’s because they contain detailed repair information as well as helpful illustrations and diagrams.

Here are some videos that explain P0661 diagnosis and repair in more detail:

How to Fix the P0651 Code

As previously mentioned, trouble codes can have multiple possible causes, each with its own set of possible solutions. These solutions can vary depending on the vehicle manufacturer. This is why there are no magic bullet solutions for DTCs. A solution to the P0651 in a Chevy truck might not be able to fix the P0651 in a VW car.

Proper troubleshooting is important before you can proceed with repairs. That said, not everyone has access to the specialized tools and know-how needed to fix and diagnose the P0651. If you’re not confident in your knowledge of DTC repairs, it’s best to have a mechanic do the job for you so you can avoid more severe problems later on.