When the P0840 code is stored, it indicates that there has been an abnormal voltage reading issuing from the transmission fluid pressure sensor circuit.
What does the P0840 code means?
In order to shift gears and offer torque converter lockup, the transmission makes use of hydraulic pressure, controlled by solenoids that are controlled by the PCM. Using the engine speed and various other factors, the PCM calculates the necessary volume of pressure at any given time to optimize vehicle operation. If the required amount of pressure and the actual pressure reading, do not match, then the code P0840 will then be stored.
What causes the P0840 trouble code?
The most regular cause of the P0840 code is a faulty electronic pressure control solenoid. However, it is equally common for dirty, contaminated, or low transmission fluid to be the issue. Other causes may include:
- A blocked transmission fluid passages.
- Mechanic internal transmission failures.
- A faulty PCM or TCM, in rare cases.
What are the symptoms of the P0840 trouble code?
Some car owners may notice no symptoms at all, and only observe the Check Engine lamp illuminating. However, the signs of the P0840 code can include:
- Loss of shifting ability.
- Lack of engagement or disengagement from the torque converter clutch.
- Harsh shifting or a slipping transmission.
- Overheated transmission.
- Decreased fuel efficiency.
- Other shift solenoid, transmission slippage, lock up, gear ratio, or torque converter clutch codes being stored in the PCM.
How can a mechanic diagnose the P0840 code?
After confirming the code with an OBD-II scanner, all transmission-related faults should start with a check of the transmission fluid. If the fluid pressure 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 fix, is performed, it’s vital to clear the code from the PCM, and retest the system. This process assists the mechanic narrow down the exact cause of the issue. If the transmission fluid fix did not make the code to disappear from the PCM, then next step is to inspect the electrical part, and to continue working through possible repairs until the correct issue is discovered.
Common mistakes made when diagnosing the P0840 code
Most of the times, the biggest error made in diagnosing and fixing the P0840 code is the tendency to change the high pressure pump, which is never in fault as often as the sensor, solenoid, or the electrical part. It’s important to begin with the small and more commonly at-fault items before replacing any major component when diagnosing the P0840 code.
How serious is the P0840 trouble code?
While some car owners may not observe any symptoms, this code still shows a serious issue that should be addressed as soon. As time goes on, car performance will decline until the car is not drivable, and ignoring this trouble code could lead to greater problems down the road.
What repairs can correct the P0840 code?
Fix to fix the P0840 code include:
- Change the pressure control solenoid.
- Refilling, or flushing and changing, the old transmission fluid.
- Clearing blocked transmission fluid passages.
- Addressing any mechanic internal transmission failures.
- Changing a faulty PCM or TCM, in rare cases.