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P0842 OBD-II Trouble Code: Transmission Fluid Pressure Sensor/Switch A Circuit Low

Check Engine Light

P0842 code definition

The P0842 code indicates that there has been an abnormally high voltage reading from the transmission fluid pressure sensor circuit. Other shift solenoid, transmission slippage, lock up, gear ratio, or torque converter clutch codes are often stored in the PCM with the P0842 code.

What the P0842 code means

The transmission uses hydraulic pressure, controlled by solenoids, which are controlled by the PCM, to shift gears and provide torque converter lockup. The PCM calculates the necessary amount of pressure at any given time to optimize vehicle operation. If the actual pressure reading is higher than the desired amount of pressure, then the code P0842 will be stored.

What causes the P0842 code?

The most common cause of the P0842 code is a faulty electronic pressure control solenoid. Other causes can include:

  • Dirty, contaminated, or low transmission fluid.
  • Blocked transmission fluid passages.
  • Mechanical internal transmission failures.
  • A faulty PCM or TCM, in very rare cases.

What are the symptoms of the P0842 code?

In some cases, only the illumination of the Check Engine lamp will be observed. However, the symptoms of the P0842 code can include:

  • Loss of shifting ability.
  • Harsh shifting or a slipping transmission.
  • Overheated transmission.
  • Decreased fuel efficiency.
  • Lack of engagement or disengagement from the torque converter clutch.

How does a mechanic diagnose the P0842 code?

After verifying the code with an OBD-II scanner, all transmission-related faults should begin with a check of the transmission fluid. If the fluid is too low, it should be refilled; if the fluid is dirty, filled with debris, or smells burnt, it may be that the entire system must be flushed, and then refilled with clean transmission fluid.

After this, or any other repair, is performed, it’s important to clear the code from the PCM, and retest the system, to ensure that no unneeded repairs are performed. If the transmission fluid fix did not cause the code to disappear from the PCM, then next step is to inspect the electrical components, and to continue working through possible repairs until the correct issue is diagnosed.

Common mistakes when diagnosing the P0842 code

Most of the time, the biggest error made in diagnosing and repairing the P0842 code is the tendency to replace the high pressure pump, rather than the sensor, solenoid, or the electrical components. It’s important to start with the small and more commonly at-fault items before replacing any major parts when diagnosing the P0842 code.

How serious is the P0842 code?

This code still indicates a serious issue that should be addressed right away, even if serious symptoms are not observed. As time goes on, vehicle performance will decline until the vehicle is not drivable. If this code is not addressed as soon as possible, it could lead to larger and more expensive repairs later on.

What repairs can fix the P0842 code?

In order to address the P0842 code, a mechanic may attempt several repairs, including:

  • Replacing the pressure control solenoid.
  • Refilling, or flushing and replacing, the old transmission fluid.
  • Clearing blocked transmission fluid passages.
  • Addressing any mechanic internal transmission failures.
  • Replacing a faulty PCM or TCM, in rare cases.

Need help with a P0842 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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