What does it mean?
This generic powertrain/drivetrain diagnostic trouble code typically applies to all OBD-II equipped vehicles, including but not limited to Chevrolet, Acura, Honda, Saturn, Jeep, Toyota, etc.
The Transmission Fluid Pressure Sensor/Switch (TFPS) is typically found attached to the side of the valve body inside the transmission, although it may sometimes be found screwed into the side of the transmission case/body itself.
The TFPS converts 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 using the vehicle’s data communication bus.
The PCM/TCM receives this voltage signal to determine transmission operating pressure or when a shift occurs. This code is set if this “B” input does not match normal operating voltages stored in the PCM/TCM memory. This may also be due to internal mechanical problems within the transmission. Refer to a vehicle-specific repair manual to determine what the “B” circuit is for your particular vehicle.
P0847 is typically an electrical circuit issue (TFPS sensor circuit). This cannot be ignored in the troubleshooting phase, especially when dealing with an intermittent problem.
Troubleshooting steps may vary depending on the manufacturer, TFPS sensor type, and wire colors.
Related Transmission Fluid Pressure Sensor B Circuit Codes:
- P0845 Transmission Fluid Pressure Sensor/Switch “B” Circuit
- P0846 Transmission Fluid Pressure Sensor/Switch “B” Circuit Range/Performance
- P0848 Transmission Fluid Pressure Sensor/Switch “B” High
- P0849 Transmission Fluid Pressure Sensor/Switch “B” Circuit Intermittent
Code Severity and Symptoms
Severity depends on which circuit the failure occurred in. Since this is an electrical failure, the PCM/TCM may compensate to some extent. The failure may mean the PCM/TCM alters transmission shifting if it is electronically controlled.
Symptoms of a P0847 engine code may include:
- Malfunction Indicator Lamp illuminated
- Change in shift quality
- Vehicle starts in 2nd or 3rd gear (limp mode)
Causes
Typically, the causes for this code to set are as follows:
- Short to ground in the signal circuit to the TFPS sensor – possible
- Failed/internally shorted TFPS sensor – probable
- Failed PCM – unlikely (programming required after replacement)
Diagnostic and Repair Procedures
A good starting point is always to check the Technical Service Bulletins (TSBs) for your particular vehicle. Your issue may be a known problem with a known fix issued by the manufacturer and could save you time and money when diagnosing.
Next, locate the Transmission Fluid Pressure Sensor/Switch (TFPS) on your particular vehicle. The TFPS is typically found attached to the side of the valve body inside the transmission, although it is sometimes screwed into the side of the transmission case/body itself. Once located, visually inspect the connector and wiring. Look for chafing, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connector 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 mounted outside the transmission case. Use electrical contact cleaner and a plastic bristle brush if cleaning the terminals is necessary. Let dry and apply electrical grease where the terminals make contact.
If you have a scan tool, clear the diagnostic codes from memory and see if the P0847 code returns. If it does not, the connections were likely your problem.
This is the most common area of concern for this code, as external transmission connections have the most corrosion issues.
If the P0847 code returns, we will need to test the TFPS sensor and its associated circuits. With the key off, disconnect the electrical connector from the TFPS sensor. Connect a black wire from the digital voltmeter (DVOM) to the ground or low reference terminal at the TFPS sensor wiring harness connector. Connect the red wire from the digital voltmeter to the signal terminal at the TFPS sensor wiring harness connector. Turn the key to the engine off position. Check manufacturer specifications; the voltmeter should read 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 previous test passed, connect one wire of an ohmmeter to the signal terminal of the TFPS sensor and the other wire to the ground or low reference terminal of the sensor. Check manufacturer specifications for sensor resistance to accurately test resistance to pressure when no pressure is applied to it. Wiggle the transmission fluid pressure sensor/switch connector while monitoring the resistance. If the ohmmeter readings do not pass, replace the TFPS.
If all previous tests passed and you continue to get a P0847, this would most likely indicate a faulty TFPS sensor, although a faulty PCM/TCM cannot be ruled out, nor can internal transmission malfunctions until the TFPS sensor has been replaced. If in doubt, seek help from a qualified automotive diagnostician. PCMs/TCMs must be programmed or calibrated to the vehicle in order to be installed correctly.