AutoCodes - Nissan - P0840 Nissan Show
- Code Popularity: 84,458 Views - Repair Importance Level: 3/3 - Repair Difficulty Level: 3/3 What is this? Table of contents By AutoCodes.com - Updated Jun 22, 2020
 What does this mean? |Code P0840 Nissan Possible Causes
|How do I Fix the Code P0840 Nissan?Check the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins. Does your Nissan have Safety Recalls? → Check here What does this mean? |Code P0840 Nissan Tech NotesThere is a factory service bulletin for the following Nissan Models: 2007-2008 Nissan Altima 2007 Nissan Maxima For Nissan vehicles with CVT transmission, Nissan has extended the CVT warranty from 5 years/60,000 to 10 years/120,000 miles
|What is the Cost to Diagnose the Code P0840 Nissan?Labor: 1.0The cost of diagnosing the P0840 Nissan code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle's make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour. |What are Code P0840 Nissan Possible Symptoms?
|Code P0840 Nissan DescriptionThe Transmission Fluid Pressure Sensor 'A' (primary pressure sensor) detects primary pressure of Continuously Variable Transmission (CVT) and sends the Transmission Control Module (TCM) the signal. The Diagnostic Trouble Code (DTC) will set when the TCM detects no signal from the Transmission Fluid Pressure Sensor 'A'. Search P0840 Nissan Questions and Answers → |Need More Information on the P0840 Nissan Code?Need more information on how to fix the P0840 Nissan code? Get Access to Factory Service Manuals |Need Help with the P0840 Nissan Code?Get the P0840 Nissan code diagnosed by a professional: Find a repair shop in your area Related Information
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code. What are the symptoms on your vehicle for the P0840 Nissan code? Have you replaced any parts? P0840 Transmission Fluid Pressure Sensor / Switch A CircuitOBD-II Trouble Code Technical DescriptionArticle by Randy Worner ASE Certified Master Technician Transmission Fluid Pressure Sensor / Switch "A" Circuit What does that mean?This generic powertrain/engine diagnostic trouble code typically applies to all OBD-II equipped vehicles including but not limited to Nissan, Dodge, Chrysler, Honda, Chevrolet, GMC, Toyota, etc. but seems to be most commonly seen on Nissan vehicles. 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 "A" 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 "A" circuit for your particular vehicle. P0840 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 A 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 P0840 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 P0840, 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 P0840. 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 P0840 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 P0840 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 P0840, 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 p0840 code?If you still need help regarding the P0840 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 low transmission fluid pressure?What Repairs Will Fix P0868?. Change the transmission fluid and filter.. Repair transmission fluid leaks.. Repair or replace damaged wiring and sensors on the transmission wiring harness.. Replace the transmission pump.. Replace transmission fluid pressure sensor.. Replace transmission fluid temperature sensor.. How do you check transmission fluid pressure switch?In order to test the switch you can connect your multimeter between the pin and the senders body. You should find the switch is closed while the engine is at rest. When the engine is running, the switch should open. As you can see this switch has only one pin, so the switch works between ground and the pin.
What does a transmission fluid pressure sensor do?The transmission oil pressure sensor's primary function is to relay information to the ECM that regulates control of the transmission. However, if the switch is damaged or not sending information correctly to the ECM, the transmission may default into "limp" mode.
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2008 Nissan Altima transmission fluid pressure sensor location
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