What are the symptoms of the P0715 fault code?
By
Vroomouk
This blog will explain the symptoms of the P0715 fault code and answer the following questions: How to fix the P0715 fault code? Can you drive a vehicle with a P0715 fault code? How much does it cost to fix the P0715 fault code?
What are the symptoms of the P0715 fault code?
The fault code P0715 occurs when there is an implausible input speed signal in the transmission control unit. Following are the symptoms of the P0715:
- Check engine light
- Abnormal jerk while shifting gears
- Vehicle in limp home mode
- Gear not shifting
All the above-mentioned symptoms are discussed in detail below:
Check engine light
The engine control unit is connected to the transmission control unit via a CAN or controller area network data bus. Therefore, when the fault code P0715 occurs in the transmission control unit due to an incorrect or no input shaft speed signal; a consequential fault code is also logged in the engine control unit.
The engine control unit receives and transmits data repeatedly to engine speed and speed of input as well as the output shaft of the transmission. This data is crucial to select the correct gear according to vehicle speed and engine load.
The engine check light will not go out until the fault has been rectified. Hence, it is necessary to diagnose and rectify the fault otherwise the driver will not be aware of any other critical faults that are present in the DTC memory of the engine control unit.
Abnormal jerk while shifting gear.
When the fault code P0715 is present in the vehicle, the transmission cannot measure the speed of the input shaft or turbine. It is connected to the flywheel through a torque convertor and as the engine is started, an input speed signal is required to change the gear from P to D or P to R.
The transmission control unit cannot determine the speed of the input shaft and when the driver selects either the D or R gear, an abnormal jerk occurs as the transmission control unit engages the output turbine.
The severity of the jerk depends on the type of engine. Petrol engines have idling speeds between 800 to 1000 RPM and the torque produced at ideal speeds is very low. Hence in some vehicles, the jerk is barely noticeable to the driver.
Vehicles with diesel engines on the other hand are heavy and deliver more torque when the engine is running at idle speed. Therefore, the jerk felt while shifting from park to drive is more severe than the petrol engine.
Constantly shifting the gear when the fault P0715 is present can cause damage to the clutch pack in the transmission housing. The torque converter can also need replacement if the vehicle is continuously driven while the fault code is still present.
Vehicle in Limp home mode
When the fault code P0715 is in the transmission control unit, the limp home mode may be activated. In limp home mode, the vehicle speed is restricted and only 2 forward or 1 reverse gear is available for the drive.
In premium cars like Mercedes Benz or BMW, the P0715 does not cause limp home mode immediately. The transmission control unit can shift through gears from the output turbine and an additional output shaft speed sensor. However, there may be abnormal jerks during the shifting of gears.
Gear not shifting
The transmission control unit has 2 to 3 turbine speed sensors located on the electrohydraulic valve body. The electrical lines cannot be checked as they are integrated into the electrical plate, therefore car manufacturers build in safeguards like limp home mode or over rev downshift protections.
If the transmission control unit detects the incorrect input speed sensor then based on the manufacturer’s software programming, the control unit will not allow the transmission to shift into drive or reverse.
The automotive transmission contains a series of planetary gear sets that are locked against the transmission housing. Hence, once the vehicle is turned off in a limp home mode, it will not allow gear changes at the next engine start.
How to fix the P0715 fault code?
The procedure to fix the P0715 is as follows:
- The fault frame freeze data is read out using a diagnostic scanner. Some transmission control units also show real-time actual values of the turbine speed sensor.
- Once the fault code is processed, a print of the test steps is taken which can be required for warranty or special goodwill claims.
- A control unit log is also generated which contains the part number of the electrohydraulic valve body and the electrical plate which houses all the RPM sensors.
- Visual inspection is carried out on the transmission, oil pan and electrical coupler. The automatic transmission oil quality is also checked for the presence of any metal particles.
- Many leading car manufacturers do not sell RPM sensors as individual spare parts. Either the complete electrical plate must be replaced or the entire electrohydraulic valve body is replaced to fix the P0715 fault code.
- After the repairs are completed, fresh transmission fluid is filled into the transmission and the transmission oil filter is also replaced.
If the individual electrical plate is not supplied as a genuine spare part and the complete electrohydraulic valve body is renewed; the initial start-up of the transmission control unit must be performed.
Can you drive a vehicle with a P0715 fault code?
Yes, it is possible to drive a vehicle with a P0715 fault code for short distances. If the vehicle is driven for extended periods of time, the transmission will go into a limp home mode. The limp home mode stays active only for one drive or ignition cycle.
When the car is turned and started again ‘ without changing gear consult to the workshop’ may appear on the instrument cluster. If the vehicle has a diesel engine then it is recommended to tow the car to any nearest workshop.
Diesel engines produce more torque than petrol engines due to heavy moving parts. There is a strong jerk when the vehicle shifts to Drive from the park or neutral. These jerks can not only damage expensive transmission components but also the transmission and engine support mounts.
How much does it cost to fix the P0715 fault code?
The repair cost to fix the P0715 fault code varies according to the car manufacturer. If the electrical plate containing the turbine RPM sensors is available then it can cost from 400 USD to 600 USD.
However, in order to avoid repeat repairs and keep the reliability, many car manufacturers recommend replacing the entire electrohydraulic valve body which can cost more than 1000 USD. The automatic transmission fluid is also replaced if it has never been replaced during the periodic service.
Other articles about Vehicle Fault Codes you may be interested in
What are the symptoms of the P2422 fault code?
Why does the fault code P0400 occur in diesel cars?
Conclusion
This blog explained the symptoms of the P0715 fault code and the procedure to fix it. The P0715 is of critical nature and it must be rectified otherwise more expensive parts like the torque converter, planetary gear sets and multi-plate clutches can get damaged.
