What is OBD-II Code P084C – Transmission Fluid Pressure Sensor/Switch H Circuit Low

What is OBD-II Code P084C – Transmission Fluid Pressure Sensor/Switch H Circuit Low

As a mechanic, one of the most common problems that vehicle owners face is the check engine light illuminating on their dashboard. When this happens, it may indicate a specific problem with their vehicle, which can be diagnosed through an On-Board Diagnostics (OBD) system. One such fault code that is often encountered is P084C, which stands for “Transmission Fluid Pressure Sensor/Switch H Circuit Low.”

When the OBD system detects a problem, it will trigger a fault code, and this fault code P084C indicates an issue with the transmission fluid pressure sensor or switch, Circuit H being the identified low-pressure circuit. This code usually affects automatic transmission vehicles, and when the vehicle is in a low-pressure state, it can cause severe issues and even a complete transmission failure. To remedy this problem, it is crucial to understand what causes it and how to repair it.

What are the causes of P084C?

Fault code P084C is usually caused by an issue in the transmission fluid pressure sensor, which measures the pressure of the transmission fluid and sends the data to the powertrain control module (PCM). Sometimes the switch in the circuit can be faulty, which disrupts the proper communication between the sensors and the PCM, this switch also puts the transmission into low-pressure mode. There are several reasons why this issue occurs, including:

– Low transmission fluid levels: When there is not enough transmission fluid, the pressure sensor cannot accurately detect the pressure in the transmission system, and the PCM may receive false signals.
– A faulty transmission fluid pressure sensor: When the sensor is faulty, it may send incorrect data to the PCM, which can trigger fault code P084C.
– A damaged wiring or connector: If the wiring or connector in the transmission fluid pressure sensor circuit is damaged, it may cause low transmission pressure, leading to the fault code.
– Problems with the transmission hydraulic circuit: This is usually the most severe cause of fault code P084C, and it requires an overhaul or complete replacement of the transmission.

How to repair P084C?

To resolve the P084C issue, it is essential first to understand the cause of the fault code. The fixes for the problem are usually specific to the cause, as explained below:

– Check and top-up transmission fluid: If low transmission fluid levels are causing the problem, it is recommended to check the fluid level using the dipstick and top it off to the recommended levels.
– Replace the transmission fluid pressure sensor: If the sensor is faulty, it may need to be replaced, so it is crucial to check the wiring, contacts, and connector pins before replacing.
– Repair or replace the wiring or connector: If the wiring or connector is damaged, you must either repair the damaged wire or replace the connector completely.
– Overhaul or replace the transmission: If the above fixes fail to resolve the fault code, the hydraulic circuit in the transmission may be damaged, requiring an overhaul or complete transmission replacement.

If you encounter P084C, we recommend consulting with a professional mechanic to diagnose the problem and ensure appropriate repair. Proper care and timely remedies can prevent significant transmission failures and other expensive problems.

Frequently Asked Questions (FAQs)

1. How do I know if my vehicle has OBD-II?
OBD-II systems are installed in all cars manufactured after 1996. You can easily find the OBD port below the dashboard on the driver’s side. You can purchase an OBD-II code reader for DIY diagnostics on your vehicle.

2. How much does it cost to fix a transmission pressure sensor?
The cost of repairing or replacing a transmission pressure sensor can vary from a few hundred to a few thousand dollars, depending on the extent of the damage and the make and model of the vehicle.

3. How often should I check my vehicle’s transmission fluid level?
It is recommended to check the transmission fluid level about once a month or every 3,000 miles, whichever occurs first. Low transmission fluid can lead to various problems, including fault code P084C.

4. Can I continue to drive my car with a fault code P084C?
It is not advisable to continue driving with a fault code P084C, as it can cause further damage to your vehicle’s transmission. It is recommended to have your vehicle inspected and repaired immediately.

5. What are the most common symptoms of a transmission fluid pressure sensor/switch H circuit low?
The most common symptoms of a transmission fluid pressure sensor/switch H circuit low include problems with shifting gears or a drop in overall power in the vehicle. In severe cases, the transmission may fail to engage entirely.


OBD-II codes can signal potential problems in your vehicle, and fault code P084C is no exception. Generally, problems with the transmission fluid pressure sensor or switch can compromise the entire automatic transmission system. It is important to have your vehicle diagnosed by a professional mechanic to understand the extent of the problem and how to resolve it. Proper care and timely service can help prevent significant transmission problems in the long run.

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