Fault code P0641 is called “Sensor Reference Voltage “A” Circuit Open” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.
Technical description and explained code P0641
Stored code P0641 means that the Powertrain Control Module (PCM) has detected an open sensor reference voltage in circuit “A”. In this case, it is not a specific sensor, but any of the sensors in circuit “A”.
Typically this circuit energizes the fuel tank pressure (FTP), barometric pressure (BARO), and fuel distributor tube pressure (FRP) sensors. As well as air conditioner refrigerant pressure and camshaft position.
All of these sensors have a 5V reference voltage on the same circuit as the PCM, and a signal is received. If this input voltage signal is not received by the PCM, the circuit is considered open and P0641 will be stored.
Thus, if an open circuit occurs in the “A” reference voltage circuit, all sensors that share this circuit may be affected. But in many cases this error will be accompanied by other codes. Which will help narrow down the general area where the circuit break is present.
Regardless of whether other codes are present or not, this error means that an open circuit exists in the “A” voltage reference circuit.
Symptoms of vehicle malfunctions
The main signal that an error P0641 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
- Additionally, there may be codes indicating a problem with a particular sensor.
- Inability to shift transmission between sport and economy modes.
- Shifts may be abrupt, or the transmission may not shift at all.
- Failure of the transmission to shift between four-wheel drive and front-wheel drive modes.
- The transfer case does not shift between high and low range.
- The speedometer may be unstable or may not work at all.
The severity of the stored fault code P0641 depends on which of the circuit sensors the breakage occurred in. Therefore, the degree of criticality will be different in each case.
Factors that can cause this error code
The error code P0641 can mean that one or more of the following problems have occurred:
- Fuel tank pressure sensor (FTP) is defective.
- Barometric pressure sensor (BARO) has failed.
- Problem with fuel distributor pipe pressure sensor (FRP).
- Faulty air conditioner refrigerant pressure sensor.
- One or more camshaft position sensors are defective.
- Problem with connection wires or connector as melted or broken.
- Fuse or fusible link blown.
- Faulty system power relay.
- Sometimes faulty PCM module is the cause.
How to fix or reset OBD-2 code P0641
Some suggested steps for troubleshooting and fix the error code P0641:
- First, connect an OBD-II scanner to the vehicle’s onboard computer and read all stored data and error codes.
- Then clear the error codes from the PCM memory and test-drive the vehicle to find out if error P0641 appears again.
- If the error code appears again, check the wires and connectors.
- Test the sensors in the “A” reference circuit, and replace if necessary.
- Check the control module (PCM), replace or reprogram if necessary.
Diagnose and repair of problems
Connect the scan tool to the vehicle’s diagnostic port and retrieve all stored codes. Then clear them and test-drive the vehicle. If code P0641 does not appear, then the error was temporary. If it appears, continue testing.
Perform a visual inspection of the wiring and connectors associated with the “A” reference circuit sensors. Replace damaged wiring or connectors if damage is detected. After that, reset the errors again, test drive and read them again.
Check the sensors
If code P0641 reappears, refer to the manual to determine which sensors are serviced by the “A” voltage reference circuit. Since manufacturers do not always follow part, circuit, and sensor labeling conventions.
Check resistance, reference voltage, continuity, and grounding continuity for all relevant sensor wiring. Compare all data obtained with the values given in the manual.
Test the operation of each sensor using an oscilloscope, a library of waveforms will be required. If such equipment and reference data are not available, continuing with the diagnostic procedure is not recommended.
Improper testing procedures can cause serious damage to the electrical system and to one or more control modules.
On which vehicles does this problem occur most frequently
Fault code P0641 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- Audi
- Cadillac
- Chevrolet (Aveo, Cobalt, Cruze, Impala, Silverado, Suburban, Tahoe, TrailBlazer)
- Daewoo (Gentra)
- Fiat (Ducato)
- Ford
- GMC (Sierra)
- Honda (Brio)
- Hover
- Hyundai (Starex)
- Land Rover (Freelander)
- Mahindra (Bolero)
- Mercedes-Benz
- Nissan (Pathfinder)
- Opel (Astra, Insignia, Mokka)
- Peugeot (Boxer)
- Renault
- Skoda (Octavia)
- Suzuki (Swift)
- Tata
- Volkswagen (Crafter, Passat, Polo, Tiguan, Touareg)
- GAZelle (Next)
- LADA (Kalina)
Fault code P0641 can sometimes be found with other errors. The most common are the following: P0642, P0643, P0651, P0697, P069E, P06A6, P1682, P2228.
