Guide To P0840 OBD Error Code Solutions

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OBD error code P0840 is an OBD-II generic code. Thought its generic, the steps to resolve it might vary a bit depending upon the specific make and model. Your vehicle will flash this OBD error code P0840 when it has few troubles with the transmission fluid pressure sensor for circuit A. If you wish to know more about this error code, you can go through our subsequent sections.

Wondering what this alien word obd P0840 actually means? Well, in a layman language we can say that it is the code that indicates a problem with transmission fluid pressure sensor “A” circuit. Your vehicle’s TFPS, also known as Transmission Fluid Pressure Sensor is located to the side of your valve body in your vehicle’s transmission system. It is responsible for converting the mechanical transmission pressure into an electrical signal for the TCM/PCM. OBD error code may start flashing because of an electrical circuit issue, but might also be set due to some mechanical issues such as broken wires or internal leaks. To know more about its few common causes, have a look at the following section.

What causes this problem Transmission Fluid Pressure Sensor/Switch "A" Circuit?

• Possible opening in the TFPS sensor signal circuit
• There is a possibility of voltage shortage in the TFPS sensor circuit
• Possible shortage to ground in the TFPS signal circuit
• Malfunctioning TFPS sensor
• Malfunctioning Powertrain Control Module

1. Transmission Control Module - You can find with us high end TCM for your beloved vehicles. Considering that P0840 error might damage transmission control module, changing them to new ones might solve your problem.
2.  Digital Voltmeter - Browse through our range of best diagnostic tools including digital voltmeters, ohm’s and much more online and be ready to become that DIY guy you always wished to be.
3. Powertrain Control Module - P0840 code might not end with just damaging your transmission system it might also damage the PCM of your vehicle. You can find powertrain control module with us for your vehicle.
4. Transmission Fluid Pressure Sensor - if you need transmission fluid pressure sensor or any other transmission system parts to correct your obd error code P0840 then you can simply browse through PartsAvatar Canada and get your hands on the best selection of parts available.
5.  Automatic Transmission Module - With us you can also find a wide variety of automatic transmission module from top auto brands to fix this OBD Error code P0840.
6. Engine Control Module - if you need engine control module to correct your obd error code P0840 then you can simply browse through PartsAvatar Canada and get your hands on the best selection of parts available.

It is essential to know the symptoms of an issue as only then you will be able to solve the problem. So that’s why we have listed out some major symptoms of OBD Code P0840 here:

Common Symptom

• Flashing of check engine light
• Changing shift quality
• Limp in mode in 2nd or 3rd gear

Here are some ways with the help of which you will be able to correct the OBD Code P0840

• Correct or replace the faulty transmission fluid pressure sensor
• Inspect all the related wiring and connectors and replace the faulty one
• Also, check your vehicle’s powertrain control module and transmission control module for any fault or defect. If found faulty, you will definitely to replace it

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Here are some steps which you should follow in order to diagnose this fault code:

To begin with check the technical service bulletins, specific to your vehicle’s make and model. This will not only help you to understand the specific issue but also help you to understand steps on how to fix it. Believe us it will save you a lot of time and money while diagnosing not only this code but for any other code too.

Also, you should start your diagnosis with all the power related error code or with the multiple code diagnosis as it will help you in understanding the reasons behind the error code P0840. Next on your list to do is to locate transmission fluid pressure sensor/switch on your vehicle to begin with the specific diagnosis. It will likely be attached to your vehicle’s valve body side inside the transmission. Once you figure out its location, next step for you to do is to check the connectors and wirings for any loose ends, bare wires, rubbing, scraping, burn spots or melted plastics. Now, take the connector apart and inspect the terminals very carefully inside the connector. Make sure that they don’t look burnt or have a green tint indicating corrosion. Make use of an electrical contact cleaner and a plastic bristle brush if cleaning of the terminals needs to be cleaned. Let dry and apply electrical grease where the terminals contact.

Now, take hold of a scan tool and clear all the existing trouble code from memory, and check if the P0840 code returns. In case it does not then the problem was mainly with the connectors only. In case it does return then the connections were most likely your problem. This is a common area of concern for this code, as the external transmission connections have the greatest number of issues with corrosion.

In case the code returns, then you will need to inspect the TFPS sensor and all the related connectors and circuits. Turn off the key and disconnect the electrical connectors at the TFPS sensor. Now, connect the digital voltmeter either to the ground or to the low reference terminal at the TFPS sensor wiring harness connector. Also connect the red lead of the DVOM to the signal terminals at the TFPS sensor wiring harness connector.

Now, turn on the key and check for the manufacturer’s specifications. Make sure that the voltmeter reads either 12 volts or 5 volts. Wiggle the connections to check if they change. In case the voltage is incorrect, repair the power or ground wire, or replace the PCM/TCM. Now, if this test is passed then 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. Next, check for the manufacturer’s specifications on the resistance of the sensor to accurately test the resistance to pressure when there is no pressure applied to it. Again, 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 you still continue to get the P0840 error code in spite of passing all these prior tests then it is signalling 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 you are in doubt, we suggest you to seek help from a trained automotive diagnostician. PCM/TCMs must be programmed or calibrated to the vehicle in order to be installed correctly.

Common Mistakes When Diagnosing the P0840 Code

Few of the common mistakes that you can commit while diagnosing this P0840 generic obd code is listed as follows:

• Failing Transmission Control Module (TCM)
• Pretty low Transmission fluid level
• Failing Transmission fluid pressure sensor
• Wiring issue