P0641 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

The ECM/PCM uses the sensor reference voltage A circuit to provide a regulated 5-volt supply to various sensors on the vehicle. When the ECM/PCM detects an open or short in the sensor reference voltage A circuit, it will set the P0641 code and illuminate the Check Engine Light.

Causes

Common causes for this code include:

• Faulty Sensor
• Damaged, corroded, broken or loose wiring and connectors
• Poor electrical connection
• Inoperative or blown fuses
• Defective system power
• Failed PCM

Symptoms

The symptoms of a P0641 code are:

• Malfunction of transmission shifting
• Failure of transmission to shift from sport to economy mode
• Delayed or no transmission engagement
• Failure of the transfer case to shift from low to high gear
• Failure of the transmission to switch between all-wheel and two-wheel drive modes
• Lack of front hub engagement
• Lack of front differential engagement
• Inoperative or erratic speedometer/odometer

Diagnosis

To diagnose a P0641 DTC code, a technician would:

1. Scan for codes in the ECM and look at the freeze frame data for failure.
2. Visually inspect the wiring and connectors for any damage or loose connections.
3. Check for any blown fuses in the ECM/PCM fuse panel.
4. Test the sensor reference voltage A circuit for an open or short.
5. If the sensor reference voltage A circuit passes all tests, then the ECM/PCM will need to be replaced.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a P0641 code:

• Not thoroughly inspecting all the wiring and connectors for damage or loose connections
• Not clearing the codes and testing the system to see if the code returns
• Failing to check for blown fuses in the ECM/PCM fuse panel
• Replacing parts without first doing a thorough diagnosis

How serious is this?

A P0641 code is a serious code because it can cause a wide variety of drivability issues. If the code is not diagnosed and repaired in a timely manner, it could lead to more serious problems such as transmission failure or engine damage.

What repairs can fix the code?

The following are solutions that may fix this problem:

• Broken or faulty wirings must be repaired or replaced as needed
• All connectors must be inspected for damage or loose connection and repaired or replaced as needed
• All fuses must be checked and replaced as needed
• The sensor reference voltage A circuit must be tested for an open or short and repaired as needed
• The ECM/PCM may need to be replaced if all other repairs fail.

Related codes

A P0641 is related to and may be accompanied by the following codes:

P0640 – Sensor Reference Voltage B Circuit Open

P0642 – Sensor Reference Voltage A Circuit Low

P0643 – Sensor Reference Voltage A Circuit High

B0000 – Body Code

C0000 – Chassis Code

U0000 – Network Code

Conclusion

In conclusion, the P0641 code is a diagnostic trouble code that refers to a problem with the voltage output from the sensor reference voltage A circuit. The code is set when the ECM/PCM detects an open or short in the sensor reference voltage A circuit. This can cause a wide variety of drivability issues and should be diagnosed and repaired as soon as possible.