P0651 OBD-II Trouble Code: Sensor Reference Voltage B Circuit Open

P0651 code definition

The P0651 indicates that the sensor reference voltage B circuit is open. This code applies to all manufacturers.

What the P0651 code means

This generic code shows that there is some type of fault in the sensor reference voltage "B", and is detected by one of the other sensor 5 voltage circuits or the engine control module or ECM. The voltage could be higher or lower than expected.

What causes the P0651 code?

A number of different things could potentially cause the P0651 code. The common causes include:

• A faulty engine control module (EMC).
• An open or shorted ECM harness.
• Poor quality electrical connection in the ECM circuit
• Shortened sensor on a 5-volt circuit.

What are the symptoms of the P0651 code?

The symptoms of a P0651 code can vary, so it is important to get an understanding of the different issues you might face. It might include a hard or no start condition, the engine could start running rough, or you might notice that the vehicle no longer has the same fuel efficiency that it once did. The engine might misfire, and you would likely notice a lack of power in the vehicle. If the trouble code is stored, and the Check Engine Light isn’t on, it might show the code as pending. However, in other cases, the engine light might be on.

How does a mechanic diagnose the P0651 code?

The Onboard Diagnostics II standardized system is a computer system in many cars and trucks today that allows the vehicle to run self-diagnostics and reports. A mechanic will utilize an OBD-II scanner to diagnose the problem with your vehicle and access data regarding the fault and necessary repair. They will examine the data to determine when a code was set, reset the codes, and then test the vehicle to determine when the code returns, if it does. In many cases, the mechanic will be able to determine the problem based on the data they receive. Determining that it is the P0651 code and not one of the other trouble codes lets them know the next actions they need to take to help get the vehicle back in shape.

Common mistakes when diagnosing the P0651 code

The biggest mistakes when dealing with the P0651 code diagnosis, or any diagnosis for that matter, is spending time looking at symptoms and stored codes that are present in the vehicle that might not have anything to do with the P0651 code. If a mechanic tries to rush through the job or skips parts of the testing process, they will not get an accurate result, and they will often misdiagnose the vehicle’s actual problems. Naturally, this will lead to repairs that do not work.

How serious is the P0651 code?

The P0651 sensor code can be a big problem for your vehicle. While it might still be possible to drive the vehicle, at least for a time, the fuel efficiency may suffer. As mentioned earlier, in some cases the vehicle will be more difficult to start, and it might not start up at all. It’s always a good idea to get any issues with your vehicle fixed as quickly as possible.

What repairs can fix the P0651 code?

The following are some of the common ways to deal with the P0651 code:

• Have a mechanic use an OBD-II scanner to check the code.
• Reset the codes, after which the mechanic will take the vehicle for a road test. In many cases, the code will not come back.
• Check the connectors, circuits, and wiring – replace if needed.
• Check the engine control module, and all components on that circuit.

Additional comments for consideration regarding the P0651 code

Many vehicles will start to have sensor issues as they get older and have more miles put onto them, and it doesn’t always mean it is a sign to worry. Have the mechanic check with the OBD-II scanner, test the vehicle, and reset the codes. Many times, the codes will not return, and you will not need to do any repairs to the vehicle. However, if the code does come back and the issues with your vehicle continue or get worse, you will want to take it in for repair.

Need help with a P0651 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.