P0642 Code: Sensor Reference Voltage “A” Circuit Low

On-board diagnostic (OBD) codes help mechanics and car owners identify issues in a vehicle. However, before you can resolve these issues, you must first understand what these codes mean.

P06xx trouble codes (xx being other numbers) indicate a fault inside the powertrain control module (PCM) or a related circuit specific to it. If your scan tool reads a P0642 code, read on to find out what it means.

What Does the P0642 Code Mean?

Diagnostic trouble code (DTC) P0642 stands for “Sensor Reference Voltage “A” Circuit Low.” 

Engine sensors receive a 5-volt reference signal from the powertrain control module (PCM). If the PCM identifies an inaccurate output signal or a voltage signal that’s lower than a programmed limit, it sets code P0642.

The P0642 code indicates that the PCM has identified a low reference voltage signal for the circuit designated “A.” The  circuit in question will vary by vehicle.  

In most cases, the P0642 code is set alongside other error codes. 

Note: The definition of code P0642 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 P0642 Code?

• Malfunctioning sensor
• Bad or blown fuses and/or fusible links
• Circuit issues, such as a damaged wire or poor connection
• An issue with the PCM

What are the Common Symptoms of the P0642 Code?

• Illuminated check engine light
• Engine and transmission problems, ranging from a no-start condition to rough running, depending on the vehicle and affected sensors

How to Diagnose the P0642 Code

The P0642 code is a generic code that can be logged on different vehicles. However, this does not mean that there is a universal solution to determining its underlying problem.

The steps for diagnosing this code can differ depending on the vehicle. Check out this video to get an idea of what the diagnostic process for this code might involve:

How to Fix the P0642 Code

The repair procedure for the P0642 code varies, depending on the vehicle’s make and model. For example, the repair steps for a P0642 Dodge might differ from the steps that will fix the same code in a P0642 Honda.

If you’re an experienced automotive DIYer, and you want to solve the issue yourself, make sure you consult a vehicle-specific repair manual or an online repair database. Alternatively, you can leave the job to a professional.