OBD-II Trouble Code Technical DescriptionArticle by  Randy Worner ASE Certified Master Technician Show Transmission Fluid Pressure Sensor / Switch "B" Circuit Range Performance Rationality What does that mean?This generic powertrain/engine diagnostic trouble code typically applies to all OBD-II equipped vehicles including but not limited to Jeep, Dodge, Mazda, Nissan, Honda, GM, etc. The Transmission Fluid Pressure Sensor/Switch (TFPS) is usually found attached to the side of the valve body inside the transmission, although sometimes it may be found screwed into the side of the transmission case/body itself. The TFPS converts the mechanical transmission pressures into an electrical signal for the Powertrain Control Module (PCM) or Transmission Control Module (TCM). Typically, the PCM/TCM will then inform other controllers utilizing the vehicle's data communication bus. The PCM/TCM receives this voltage signal to determine transmission operating pressure or when a shift is occurring. This code is set if this "B" input does not match normal operating voltages stored in the PCM/TCM's memory. It may also be due to internal mechanical issues inside the transmission. Refer to a vehicle specific repair manual to determine which is the "B" circuit for your particular vehicle. P0846 is typically an electrical circuit (TFPS sensor circuit) issue, although as previously stated this code may also be set due to mechanical issues (internal leaks, cracked or missing check balls in the valve body, low system operating pressure/main line pressure, stuck valve in the valve body). This cannot be overlooked in the troubleshooting stage, especially when dealing with an intermittent problem. Troubleshooting steps may vary depending upon manufacturer, type of TFPS sensor and wire colors. Related trans fluid pressure sensor B circuit codes:
Code Severity & SymptomsSeverity depends upon which circuit the failure has occurred in. Since this is an electrical failure, the PCM/TCM can compensate to some degree. The failure may mean that the PCM/TCM modifies the shifting of the transmission if electronically controlled. Symptoms of a P0846 engine code may include:
CausesTypically the causes for this code to set are:
Diagnostic and Repair ProceduresA good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis. A good example of this would be if there are any known power related codes set along with the P0846, or if there is more than one pressure sensor/switch code set. If so, begin your diagnosis with the power related fault code first, or with the multiple code diagnosis first, as this may be the reason for the P0846. Next, locate the Transmission Fluid Pressure Sensor/Switch (TFPS) on your particular vehicle. The TFPS is usually found attached to the side of the valve body inside the transmission, although sometimes it may be found screwed into the side of the transmission case/body itself. Once located, visually inspect the connector and wiring. Look for scraping, rubbing, bare wires, burn spots or melted plastic. Pull the connector apart and carefully inspect the terminals (the metal parts) inside the connector. See if they look burned or have a green tint indicating corrosion, especially if they are attached outside the transmission case. Use electrical contact cleaner and a plastic bristle brush if cleaning of the terminals is needed. Let dry and apply electrical grease where the terminals contact. If you have a scan tool, clear the diagnostic trouble codes from memory, and see if P0846 code returns. If it does not, then the connections were most likely your problem. This is the most common area of concern for this code, as the external transmission connections have the greatest number of issues with corrosion. If the P0846 code does return, we will need to test the TFPS sensor and its associated circuits. With the Key Off, disconnect the electrical connector at the TFPS sensor. Connect a Digital Voltmeter (DVOM) black lead to the ground or low reference terminal at the TFPS sensor wiring harness connector. Connect the red lead of the Digital Voltmeter to the signal terminal at the TFPS sensor wiring harness connector. Turn Key On Engine Off. Check manufacturer's specifications; voltmeter should read either 12 volts or 5 volts. Wiggle the connections to see if they change. If the voltage is incorrect, repair the power or ground wire, or replace the PCM/TCM. If the prior test passed, connect one lead of an ohmmeter to the signal terminal at the TFPS sensor and the other lead to the ground or low reference terminal at the sensor. Check manufacturers specifications on the resistance of the sensor to accurately test the resistance to pressure when there is no pressure applied to it. Wiggle the connector at the Transmission Fluid Pressure Sensor/Switch while monitoring the resistance. If the ohmmeter readings do not pass, replace the TFPS. If all prior tests have passed and you continue to get a P0846, this would most likely indicate a failed TFPS sensor, although a failed PCM/TCM could not be ruled out, nor could internal transmission malfunctions until the TFPS sensor had been replaced. If unsure, seek assistance from a trained automotive diagnostician. PCM/TCMs must be programmed, or calibrated to the vehicle in order to be installed correctly. Related DTC Discussions
Need more help with a p0846 code?If you still need help regarding the P0846 trouble code, please post your question in our FREE car repair forums. NOTE: This information is presented for information purposes only. It is not intended as repair advice and we are not responsible for any actions you take on any vehicle. All information on this site is copyright protected. How do you fix P0845?What repairs can fix the P0845 code?. Replace a faulty electronic pressure control solenoid.. Replace a faulty transmission fluid sensor.. Cleaning blocked transmission fluid passages.. Addressing any internal transmission failures.. Refilling low transmission fluid.. How do I fix code P0843?What repairs can fix the P0843 code?. The most common repairs for a P0843 are as follows:. Replacing the transmission fluid pressure sensor.. Replacing the transmission fluid pressure control solenoid.. Replacing and flushing the transmission fluid.. Repairing damaged or blocked fluid hoses.. How do I fix code P0842?What repairs can fix the P0842 code?. Replacing the pressure control solenoid.. Refilling, or flushing and replacing, the old transmission fluid.. Clearing blocked transmission fluid passages.. Addressing any mechanic internal transmission failures.. Replacing a faulty PCM or TCM, in rare cases.. |
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