Transmission gears provide varying levels of torque and speed, enabling your vehicle to drive smoothly. As such, being able to shift gears is important. When error codes like P0842 are stored, they often indicate problems with the vehicle’s transmission, which can lead to shifting problems.
Learn more about what code P0842 means, what causes it, and how you can fix it.
What Does Code P0842 Mean?
The P0842 code stands for “Transmission Fluid Pressure Sensor/Switch “A” Circuit Low.” Diagnostic trouble code (DTC) P0842 is one among several codes in your vehicle’s On-Board Diagnostics II (OBD-II) system that indicate a problem with the transmission fluid pressure sensor/switch. Vehicle makes like Honda, Acura, and Chevy have been reported to store the P0842 code.
The transmission fluid pressure sensor/switch (TFPS) is located on the side of the valve body inside the transmission, although depending on the model of your vehicle, may also be found screwed into the side of the transmission body itself. The TFPS converts the mechanical transmission pressures into signals for the powertrain control module (PCM) to interpret. When the TFPS input fails to meet the expected value stored in the PCM, error code P0842 is stored.
Honda’s service manual notes that when error code P0842 is stored, it is usually due to an electrical circuit problem and not a mechanical problem in the transmission.
What Causes Code P0842?
A variety of reasons can cause the error code P0842 to be stored. Some common causes include:
- Faulty TFPS
- Circuit problems
- Low transmission fluid level
- Malfunctioning PCM
Faulty TFPS
A malfunctioning TFPS may provide incorrect pressure readings, triggering the P0842 code. This can be due to sensor wear, internal damage, or contamination.
Circuit Problems
Wiring issues like shorts or corroded connectors in the TFPS circuit can disrupt communication with the PCM. Poor electrical continuity affects sensor performance and accuracy in readings.
Low Transmission Fluid Level
Insufficient fluid level leads to inadequate hydraulic pressure, causing erratic transmission operation.
Malfunctioning PCM
A defective or failing PCM can misinterpret signals from the pressure sensor or fail to properly control transmission function, even if the sensor itself is functioning correctly.
What Are the Symptoms of Code P0842?
As with many other DTCs, the first and most common symptom of error code P0842 is an illuminated check engine light. Here are the specific symptoms you should look out for:
- Check engine light
- Improper transmission shifting
- Vehicle starts in limp mode
Check Engine Light
As mentioned, the first symptom you will likely observe when your vehicle stores code P0842 is an illuminated check engine light.
Improper Transmission Shifting
The transmission may shift roughly, erratically, or get stuck in a single gear due to faulty pressure readings. This may lead to poor drivability, reduced fuel efficiency, and potential damage to transmission components if left unresolved.
Vehicle Starts in Limp Mode
Limp mode may be activated to prevent further damage when the transmission pressure sensor malfunctions. In this mode, the transmission is locked into a single gear, limiting speed and drivability.
How to Diagnose Code P0842
It may feel daunting, diagnosing code P0842 if you’ve never done it before, but you’ll find it relatively straightforward as long as you have the knowledge and the right tools. Here are some troubleshooting steps for diagnosing error code P0842:
Check Technical Service Bulletins (TSBs)
Checking known TSBs specifically for your vehicle is a good place to start when diagnosing code P0842. It may be a known issue with an established fix provided by the vehicle manufacturer.
Review Stored DTCs
There may be more than one stored DTC that’s affecting your vehicle’s drivability. Plug in your OBD-II scanner and review its stored codes to rule out all possible issues your vehicle may be experiencing.
Check Transmission Fluid
Check the condition and level of the transmission fluid. Dirty, burnt, or low fluid can affect sensor performance and should be replaced or topped up as needed.
Inspect Transmission Fluid Pressure Sensor
Locate the transmission fluid pressure sensor and conduct a visual inspection. Check for signs of physical damage, corrosion, or misalignment.
Check PCM/TCM
A failing PCM/TCM is most likely the cause if you continue to receive a P0842 after thorough testing. Correct installation of PCM/TCMs requires that they be calibrated or programmed to the vehicle.
How to Fix Code P0842
Once you’ve determined the root cause of the P0842 error code, it’s time to fix the issue. Keep in mind that there’s no single solution for OBD-II codes. That said, here are some common fixes for the P0842 code:
Repair or Replace Defective TFPS
If your diagnosis has determined that the TFPS is the problem, installing a new sensor should restore accurate pressure readings and proper transmission operation.
Flush and Fill Transmission Fluid
Do this fix only if your vehicle has contaminated transmission fluid. Perform a fluid flush and replace with fresh new fluid to ensure the transmission operates smoothly.
Repair or Replace Faulty Wiring or Connectors
Inspect the TFPS circuit for damaged wires, poor connections, or corrosion. Repairing or replacing compromised electrical components restores proper communication between the sensor and PCM, resolving the low circuit issue.
Address Mechanical Transmission Issues
Internal transmission problems, such as blocked fluid passages or component failures, can cause abnormal pressure readings. Addressing these properly should resolve the code.
Replace PCM
Although rare, a failing PCM can misinterpret or fail to process the sensor's signals correctly. If all other potential issues are ruled out, replacing the PCM may be necessary.
Other Codes Related to P0842
DTCs related to P0842 involve errors with the transmission range sensor. These are some related codes that could also appear if you’re dealing with ECM problems:
P0840
Error code P0840 is stored when the PCM/TCM receives a voltage signal different from the normal operating voltages stored within it.
P0841
The P0841 code is logged when there is a possible problem with the transmission fluid pressure sensor or switch "A" circuit. It means that the PCM has detected an issue with the transmission fluid pressure.
P0843
Code P0843 is triggered when the PCM detects a voltage signal from the transmission fluid pressure sensor (TFPS) that is different from normal.
P0844
A stored P0844 indicates a problem with the transmission fluid pressure sensor or switch "A" circuit.
FAQ
How much does it cost to replace a transmission fluid pressure sensor?
The cost to replace a transmission fluid pressure sensor depends on the make, model, and year of your vehicle, as well as on local labor rates. On average, the cost to replace a transmission fluid pressure sensor ranges from $15 to $150.