Error Code P0868 is referred to as Transmission Fluid Pressure Low. This is a generic trouble code, meaning it applies to vehicles equipped with the OBD-II system, particularly those made from 1996 up to present. Specifications on the definition, troubleshooting, and repairs may vary depending on the manufacturer, year model, and powertrain configuration.
Error Code P0868 is set when the Powertrain Control Module (PCM) finds out that the transmission fluid pressure is lower than expected or minimum allowable value.
Vehicles with automatic transmission use pressured transmission fluid to engage or disengage the clutch pucks and other components, especially the lock-up torque converter clutch, to complete gearshifts. This pressure, however, is not constant. In some cases, the pressure is relieved temporarily when specific transmissions are moved. In a fully functional system, the internal pressure pump (usually driven by the engine) provides the pressure. The PCM directs pressurized fluid into various hydraulic passages through electronically controlled solenoids and other valves to shift the transmission.
Thus, when the pressure falls below the minimum specified limit set, the PCM or the Transmission Control Module (TCM) will not be able to initiate the gearshifts, since the is required minimum pressure to initiate the gearshift is not met on the one hand, and maintain gear selection on the other. The keep a selected gear, the transmission fluid pressure must be adequate to keep the present selected clutch pack from slipping.
To monitor transmission fluid pressure, transmissions are fitted with pressure-sensitive sensors which transmit actual fluid pressure to the PCM continuously. The sensor is usually supplied with a 5V reference voltage by the PCM. When the fluid pressure change, the resistance in the sensor also changes with more or less current (aka signal voltage) sent back to the PCM.
The PCM then interprets the signal voltage as pressure and will set the Error Code P0868 and activate the Check Engine light if it sees that the transmission fluid pressure is lower than the specified value.
In some cases, the PCM may initiate the fail-safe or limp mode to protect the transmission.
- Strong burning smell from overheated transmission
- Failing or slipping transmission
- Insufficient transmission fluid level due to leak
- Slipping or malfunctioning transmission
- Defective transmission high-pressure pump
- Defective transmission temperature sensor
- Overheating engine
- Defective PCM (rare)
How to Check
As with most error codes, this code must be diagnosed with a standard OBD-II code scanner.
Use the scanner to retrieve the freeze frame data along with other trouble codes. The code will reset if there are no drivability issues detected beforehand if the vehicle is restarted. If the code doesn’t come back, it was likely triggered incorrectly.
If the code remains, then continue the diagnosis by inspecting the transmission fluid levels. If the fluid level is low, then you can assume that there’s a leak in the system. Search where the leak is and fix it. Depending on the location of the leak, it may be possible to repair, and the issue may be resolved. In cases that suggests further damage to the transmission; the transmission must be removed and rebuilt, if not replaced.
If there is an adequate level of transmission fluid, then proceed on checking the transmission temperature sensor. Only after this step should you proceed on searching for more severe problems, such as malfunctioning PCM or failed transmission.
Repairing or replacing the faulty components should get rid of the error code once the vehicle is restarted.
How to Fix
- Repair of leaks in the transmission system
- Replacement of transmission temperature sensor
- Replacement of transmission high-pressure pump
- Rebuild or replacement of transmission
- Replacement of PCM (rare)
This error code is pretty severe as it can damage the transmission. Even if the vehicle can operate normally, it mustn’t be driven if this code is present, as it can cause complete damage to the transmission, which is both dangerous and expensive.