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P2711 is a diagnostic trouble code (DTC) for "Unexpected Mechanical Gear Disengagement". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
A P2711 fault code is generated when the transmission control module (TCM) or powertrain control module (PCM) detects a problem between the output shaft speed signals and the input shaft speed signals. The control module perceives this problem as a mechanical disengagement of the gears, and can result in poor shift quality and drivability issues.
An unexpected mechanical gear disengagement occurs when the PCM suspects that the output shaft speed sensor is malfunctioning in some way. The way the code is programed varies from manufacturer to manufacturer, but the basic idea is that the system will detect an error when the gears are, or are about ready, to shift. If the output speed is not gradually increasing (an increase that occurs until a gear shift is complete), as it does with normal functioning, then the system will detect an error. Some makes and models will require many system failures before a service engine light is triggered.
The most common causes of the P2711 code are due to a malfunctioning output speed sensor or an input speed sensor. There can also be other mechanical failures that cause the code to trigger including:
There are many noticeable associated symptoms of the P2711 code, but this is not always the case:
The P2711 code can be properly diagnosed with an advanced scanner (OBD-II scan tool) and a digital voltmeter, and, in some cases, an oscilloscope. If the scanning indicates an erratic output signal, as opposed to an erratic input signal, then the technician can assume that the unexpected mechanical gear disengagement is due to a problem with the output speed sensor, and make the diagnosis as such.
In other cases, mechanical problems are possible, i.e. damaged gears and/or drive shafts. At this point, any leaks in the transmission should be repaired, and the proper transmission fluid should be drained and refilled. If the drained transmission fluid is “burnt”, the transmission will most likely be irreparable. If not, the transmission will be used under normal conditions for tests and reassessment.
One common mistake when misdiagnosing the P2711 code is attempting to diagnose the problem as a fault with engine speed, rather than a problem with internal transmission speeds. Another common misdiagnoses is replacing the vehicle speed sensor, when the problem is in fact the transmission. A proper visual inspection of the transmission, along with a digital inspection of the electrical system components with the proper tools, can help avoid misdiagnoses. Additional inspections and tests may be necessary.
The P2711 code might cause the following problems with your vehicle:
In some cases, a check engine light may be the only noticeable symptom of a P2711 fault. Even if there are no noticeable problems while driving, you should have the vehicle checked immediately to determine and resolve the issue to avoid future damages and/or dangers while using a vehicle while the Service Engine light is triggered.
The most common procedures to resolve problems associated with the P2711 code are as follows:
Use a code reader/scanner, voltmeter, or oscilloscope to diagnose the code and to determine how the input and output speed signal is registering by the PCM.
A visual inspection of all wiring, connectors and components will be part of the initial inspection. Any wires that are damaged, contaminated, or corroded will need to be replaced.
Even if the PCM is registering the input and/or output signal as erratic, indicating an unexpected mechanical gear disengagement, it is possible the error is coming from the transmission itself, from a failing gear or shaft. In any case, the transmission will need to undergo a thorough inspection. In some cases, the transmission will need to be taken out and/or replaced.
In the event that the transmission checks out after inspection, one or more sensors might need to be replaced.
A technician might clear the OBD-II codes to see which ones return. If no codes return, the situation might be intermittent, which is difficult to diagnose. In some cases, the situation might need to worsen before a correct diagnosis can be made.
In rare cases, after testing, a technician might need to repair or replace certain electrical components of the transmission control system, according to manufacturer’s specifications. Afterwards, they will retest to make sure repairs are up to spec with manufacturer’s standards. Any electrical replacements will require reprogramming of the PCM.
It is possible that electrical-related codes occur constantly or intermittently. In the situation where the codes occur intermittently, additional time might be necessary for the situation to worsen before the issue can be properly diagnosed. The nature of a triggered P2711 code is diverse, and a solution can range from easy to diagnose and fix, to time consuming and difficult. Depending on your vehicle’s make, model and year, determining the root cause of the issue and resolving it might take several hours.
Most diagnoses, when tested with a voltmeter and/or oscilloscope, are very specific and involve many systems and components. If tests of the electronic system determine that the system is functioning properly, further inspection of the transmission will be necessary to determine whether or not the issue is mechanical, which can also require multiple test and several hours.
In some cases, and usually with vehicles with high mileage, the transmission might need to be replaced, or undergo a rebuild. However, replacing certain parts based on an assumed common issue is not recommended since no problem has been positively diagnosed. Assuming a quick fix could cause more problems, or simply render the issue unsolved.
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