An automatic transmission operates by converting the engine’s rotational force into hydraulic pressure. This pressure is then used to do things like change gears and propel you down the road. But if there is an inconsistency between how much hydraulic pressure the ECU wants, and the amount that is actually available, a P0840 DTC will be set.
How Serious is the Code?
A P0840 diagnostic trouble code, is fairly serious and can result in a number of transmission problems that include erratic shifting behavior and transmission overheating.
Symptoms of a P0840 include:
- Delayed, harsh or erratic shifts
- Transmission not able to shift gears
- Torque converter clutch failure
- Transmission overheating
- Reduced fuel economy
- Insufficient transmission fluid
- Dirty transmission fluid / filter
- Frayed wiring / damaged connectors
- Faulty transmission pump
- Torque convertor problems
- Failing transmission fluid pressure sensor
- Failing pressure control solenoid
- Failing pressure regulator
- Pressure blockage
- Valve body issue
- TCM failure
- Transmission fluid leak
How to Diagnose the Code?
When trying to determine the cause of a P0840 OBDII trouble code, it’s important to first look at the condition and level of transmission fluid. Any dirt and debris can reduce the hydraulic pressure and cause the transmission problems that are associated with this code. The wiring and connectors may also need to be inspected, along with any electrical switches that are related to hydraulic pressure. After that, more in-depth diagnosis of the transmission’s mechanical components may be needed.
What Repairs Will Fix P0840?
- Change transmission fluid and filter
- Repair leaks
- Repair or replace damaged wiring and connectors
- Replace transmission fluid pressure sensor
- Repair or replace torque converter
- Repair or replace valve body
- Replace transmission pump
- Replace pressure control solenoid
- Replace pressure regulator
- Reprogram or replace TCM