P0641 Open circuit of sensor A reference voltage

OBD-II Trouble Code - P0641 - Data Sheet

P0641 - Sensor A Reference Voltage Circuit Open

What does trouble code P0641 mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may differ depending on the brand / model.

When I find a stored code P0641, it means the powertrain control module (PCM) has detected an open circuit for a specific sensor; denoted in this case as "A". When diagnosing an OBD-II code, the term "open" can be replaced with "missing".

The sensor in question is usually associated with an automatic transmission, transfer case, or one of the differentials. This code is almost always followed by a more specific sensor code. P0641 adds that the circuit is open. Consult a reliable source of vehicle information (All Data DIY is a great choice) to determine the location (and function) of the sensor related to the vehicle in question. If P0641 is stored separately, suspect a PCM programming error has occurred. Obviously, you will need to diagnose and repair any other sensor codes before diagnosing and repairing P0641, but be aware of the "A" open circuit.

A voltage reference (typically five volts) is applied to the sensor in question through a switchable (key-powered) circuit. There should also be a ground signal. The sensor is likely to have a variable resistance or electromagnetic variety and is closing a specific circuit. The resistance of the sensor decreases with increasing pressure, temperature or speed and vice versa. Since the resistance of the sensor changes with conditions, it supplies the PCM with an input voltage signal. If this voltage input signal is not received by the PCM, the circuit is considered open and P0641 will be stored.

The Malfunction Indicator Lamp (MIL) may also be illuminated, but be aware that some vehicles will take multiple driving cycles (with a malfunction) for the MIL to turn on. For this reason, you must allow the PCM to enter standby mode before assuming that any repair is successful. Just remove the code after repair and drive as normal. If the PCM goes into readiness mode, the repair was successful. If the code is cleared, the PCM will not go into ready mode and you will know that the problem still exists.

Severity and symptoms

The severity of a stored P0641 depends on which sensor circuit is in the open state. Before you can determine the severity, you need to review the other stored codes.

Symptoms of a P0641 code may include:

• Inability to switch the transmission between sport and economy modes
• Gear shift malfunctions
• Delay (or lack) of turning on the transmission
• Transmission failure to switch between XNUMXWD and XNUMXWD
• Failure of the transfer case to switch from low to high gear
• Lack of inclusion of the front differential
• Lack of engagement of the front hub
• Incorrect or not working speedometer / odometer

Causes of the P0641 code

Possible causes of this engine code include:

• Open circuit and / or connectors
• Defective or blown fuses and / or fuses
• Faulty system power relay
• Bad sensor
• Defective engine control module (ECM)
• ECM harness open or shorted
• Bad electrical circuit ECM
• The sensor is shorted to 5 volts What does this mean?

Diagnostic and repair procedures

To diagnose a stored P0641 code, I will need access to a diagnostic scanner, a digital volt / ohmmeter (DVOM), and a trusted source of vehicle information (such as All Data DIY). A handheld oscilloscope can also be useful under certain circumstances.

Use your vehicle's information source to determine the location and function of the sensor in question as it relates to your specific vehicle. Check system fuses and full load fuses. Fuses that may appear normal when the circuit is very lightly loaded, often fail when the circuit is fully loaded. Blown fuses should be replaced, keeping in mind that a short circuit is likely the cause of the blown fuse.

Visually inspect the harness and connectors associated with the sensor system. Repair or replace damaged or burnt wiring, connectors, and components as needed.

Then I connected the scanner to the car diagnostic socket and got all stored DTCs. I like to write them down along with any associated freeze frame data, as this information can be helpful if the code turns out to be choppy. After that, I would go ahead and clear the code and test drive the car to see if it resets immediately.

If all system fuses are OK and the code resets immediately, use the DVOM to test the reference voltage and ground signals on the sensor in question. Generally, you should expect to have five volts and a common ground at the sensor connector.

If voltage and ground signals are present at the sensor connector, continue testing the sensor resistance and integrity levels. Use your vehicle information source to get test specifications and compare your actual results with them. Sensors that do not meet these specifications should be replaced.

Disconnect all related controllers from the system before testing resistance with the DVOM. If there is no voltage reference signal at the sensor, disconnect all associated controllers and use the DVOM to test the circuit resistance and continuity between the sensor and the PCM. Replace open or shorted circuits as necessary. If using a reciprocating electromagnetic sensor, use an oscilloscope to track the data in real time; paying particular attention to glitches and fully open circuits.

Additional diagnostic notes:

• This type of code is usually provided as support for more specific code.
• A stored code P0641 is usually associated with the transmission.

P0641 BRAND SPECIFIC INFORMATION

• P0641 ACURA Sensor Reference Sensor “A” Malfunction
• P0641 BUICK 5 Volt Incorrect reference voltage
• P0641 CADILLAC Incorrect reference voltage 5 volts
• P0641 CHEVROLET 5V reference voltage incorrect
• P0641 GMC 5 Volt Incorrect reference voltage
• P0641 HONDA Sensor Reference Voltage Malfunction "A"
• P0641 HYUNDAI Sensor Reference Sensor “A” Circuit Open
• P0641 ISUZU 5V reference voltage incorrect
• P0641 KIA Sensor “A” Reference Voltage Circuit Open
• P0641 Invalid reference voltage PONTIAC 5V
• P0641 Saab 5V Reference Voltage Incorrect
• P0641 SATURN Incorrect reference voltage 5 volts
• P0641 SUZUKI 5V reference voltage incorrect
• P0641 VOLKSWAGEN reference voltage sensor circuit open "A"

What is P0641 Engine Code [Quick Guide]

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