P0840 Transmission fluid pressure sensor/switch A circuit

P0840 – OBD-II Trouble Code Technical Description

Transmission Fluid Pressure Sensor/Switch Circuit "A"

What does the fault code mean P0840?

An automatic transmission converts the engine's rotational force into hydraulic pressure to change gears and move you down the road. Code P0840 can occur due to a discrepancy between the ECU's required hydraulic pressure and actual pressure, which is usually associated with the transmission fluid pressure sensor/switch (TFPS). This is a common problem for many brands, including Nissan, Dodge, Chrysler, Honda, Chevrolet, GMC, Toyota and others. Repair steps may vary depending on the manufacturer and type of TFPS sensor. Related codes related to transmission fluid pressure include P0841, P0842, P0843, and P0844.

Possible reasons

Reasons for setting a P0840 code include:

• Open circuit in the signal circuit to the TFPS sensor
• Short to voltage in the TFPS sensor signal circuit
• Short to ground in TFPS signal circuit
• Faulty TFPS sensor
• Internal problem with manual transmission
• Lack of transmission fluid
• Contaminated transmission fluid/filter
• Worn wiring/damaged connectors
• Transmission fluid leak
• Transmission control module (TCM) problems
• Internal transmission failure
• Valve body problems.

What are the symptoms of a fault code? P0840?

Reasons for setting a P0840 code include:

• Open circuit in the signal circuit to the TFPS sensor
• Short to voltage in the TFPS sensor signal circuit
• Short to ground in TFPS signal circuit
• Faulty TFPS sensor
• Internal problem with manual transmission
• Lack of transmission fluid
• Contaminated transmission fluid/filter
• Worn wiring/damaged connectors
• Transmission fluid leak
• Transmission control module (TCM) problems
• Internal transmission failure
• Valve body problems.

How to diagnose a fault code P0840?

Deciphering the P0840 code can be challenging. When this error appears, there may be problems with the wiring, TFPS sensor, TCM, or even internal transmission problems. It is recommended to start by checking the Technical Service Bulletins (TSBs) and perform a visual inspection of the TFPS connector and wiring. For diagnostics, you can use a digital voltmeter (DVOM) and an ohmmeter. If any faults are found, the relevant components should be replaced and the PCM/TCM units programmed for your vehicle. If in doubt, it is better to contact a qualified automotive diagnostician.

Diagnostic errors

When diagnosing a P0840 code, common errors may include:

1. Insufficient checking of technical service bulletins (TSBs) for known issues and fixes related to this code.
2. Incomplete or poor inspection of the wiring and connectors leading to the transmission fluid pressure sensor (TFPS).
3. Poor interpretation of diagnostic results, especially regarding manufacturer specifications for resistance and voltage.
4. Failure to check for internal transmission problems such as leaks, pressure blockages or valve body problems.
5. Neglecting to properly program or calibrate the PCM/TCM after replacing components.

Given the difficulty of diagnosing this problem, it is recommended that you contact a qualified technician or auto repair shop for accurate and effective diagnosis and repair.

How serious is the fault code? P0840?

Trouble code P0840 indicates a problem in the transmission control system related to the transmission fluid pressure sensor/switch. Depending on the specific cause and conditions of use of the vehicle, the severity of this code may vary. Some of the possible consequences may include unusual gear shifting, increased fuel consumption, or other transmission problems.

It is important to pay attention to the symptoms and begin diagnosis and repair immediately to avoid worsening the problem and possible damage to the transmission. It is recommended to contact a qualified specialist for more accurate diagnosis and troubleshooting.

What repair will help eliminate the code? P0840?

The following repairs may be required to resolve the P0840 code:

1. Check and replace damaged or broken wires in the transmission fluid pressure sensor/switch (TFPS) circuit.
2. Replacing a faulty transmission fluid pressure sensor/switch.
3. Checking and servicing transmission fluid, including replacing the filter and removing contaminants.
4. Diagnose and, if necessary, replace the transmission control module (TCM) or engine control module (PCM) if the problem is related to them.
5. Check and repair any internal transmission problems such as leaks, pressure blockages or valve body problems.

It is recommended that you contact a qualified technician or auto repair shop for a more accurate diagnosis and appropriate repair work.

What is P0840 Engine Code [Quick Guide]

P0840 – Brand-specific information

The meaning of the P0840 code may vary depending on the make and model of the vehicle. Here are some decodings for specific brands:

1. For Ford vehicles: P0840 may indicate a problem with the transmission fluid pressure sensor circuit.
2. For Toyota vehicles: P0840 may indicate a failure in the transmission fluid pressure sensor circuit.
3. For BMW vehicles: P0840 may indicate a faulty or signal problem with the transmission fluid pressure sensor.
4. For Chevrolet vehicles: P0840 may indicate a problem with the transmission fluid pressure control circuit.

Given the differences between makes and models, it is recommended that you consult your specific vehicle's owner's manual or repair manual for more accurate information.