P0991 Transmission fluid pressure sensor "E" circuit intermittent/erratic
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P0991 ā OBD-II Trouble Code Technical Description
Trouble code P0991 indicates an intermittent/intermittent signal in the transmission fluid pressure sensor "E" circuit.
What does the fault code mean P0991?
Trouble code P0991 indicates a signal problem in the transmission fluid pressure sensor "E" circuit. This means that the automatic transmission control system has detected instability or intermittency in the signal coming from the transmission fluid pressure sensor "E". The transmission fluid pressure sensor plays an important role in gear shifting and proper torque converter operation by controlling solenoid valves that regulate pressure and are controlled by the PCM (engine control module). Trouble P0991 occurs when the PCM detects that the transmission fluid pressure is outside the manufacturer's specified range. When this code appears, the Check Engine light turns on. The PCM determines the required pressure based on throttle position, vehicle speed, engine load and engine speed.
Possible reasons
Some possible reasons for the P0991 trouble code:
- Transmission fluid pressure sensor malfunction: The sensor itself may become damaged or fail due to wear or improper operation.
- Damaged or broken wiring: Problems with the wiring, connections, or connectors associated with the transmission fluid pressure sensor can cause the P0991 code.
- Problems with the car's electrical system: For example, grounding problems or a short circuit in the transmission control system can cause signal instability.
- Engine Control Module (PCM) Problems: Malfunctions or errors in the PCM, which manages the signals and processing of data from the transmission fluid pressure sensor, can also cause the P0991 code to appear.
- Transmission fluid problems: Insufficient or contaminated transmission fluid can also cause inconsistent signals from the pressure sensor.
These are just a few common reasons, and the actual cause may depend on the specific make and model of the car. To accurately determine the cause, it is recommended to conduct a detailed diagnosis using appropriate equipment and tools.
What are the symptoms of a fault code? P0991?
Symptoms for a P0991 trouble code can vary depending on the specific problem and vehicle characteristics, some possible symptoms that may occur are:
- Gearshift problems: The automatic transmission may become unstable or shift incorrectly between gears.
- Unusual sounds or vibrations: You may experience unusual noises or vibrations when shifting gears or driving due to improper transmission operation.
- Changes in engine operation: If there are problems with the transmission and transmission fluid pressure, changes in engine performance may occur, such as unstable idle speed or rough operation when accelerating.
- Increased fuel consumption: Improper transmission operation can result in increased fuel consumption due to improper gear shifting and poor engine performance.
- Turning on the Check Engine Light: Trouble code P0991 activates the Check Engine Light on your vehicle's dashboard, indicating problems with the transmission or engine management system.
If you notice any of these symptoms or your check engine light comes on, it is recommended that you immediately contact a qualified auto mechanic to diagnose and repair the problem.
How to diagnose a fault code P0991?
The following steps are recommended to diagnose DTC P0991:
- Checking the Check Engine indicator: Check to see if there is a Check Engine light on your vehicle's dashboard. If yes, write down error code P0991.
- Using the diagnostic scanner: Connect the diagnostic scanner to the vehicle's OBD-II port and read the error codes. Make sure the P0991 code is listed.
- Checking the transmission fluid level: Check the level and condition of the transmission fluid according to the vehicle manufacturer's recommendations. Leaks or insufficient fluid levels can lead to pressure problems.
- Wiring check: Visually inspect the wiring, connections and connectors associated with the transmission fluid pressure sensor. Make sure there is no damage, breaks or corrosion.
- Pressure sensor testing: Check the functionality of the transmission fluid pressure sensor using a multimeter or other suitable tool. Verify that the signals from the sensor meet the manufacturer's specifications.
- Additional diagnostics: If necessary, perform additional tests and inspections, such as checking the sensor circuit voltage and resistance, and testing the engine control module (PCM).
- Elimination of identified problems: Once the cause of the problem has been identified, carry out the necessary repairs or replacement of parts.
If you are unable to determine the cause of the P0991 code yourself or perform the necessary repair work, it is recommended that you contact a professional auto mechanic or auto repair shop for further diagnosis and repair.
Diagnostic errors
When diagnosing DTC P0991, the following errors may occur:
- Incorrect interpretation of the code: Interpreting the P0991 code without context or without fully diagnosing other transmission components may lead to incorrect conclusions.
- Faulty wiring diagnostics: Improperly diagnosing the wiring associated with the transmission fluid pressure sensor can lead to missed opens, corrosion, or other electrical problems.
- Incorrect pressure sensor testing: Incorrect testing or interpretation of the transmission fluid pressure sensor test results may lead to incorrect conclusions about its performance.
- Malfunction of other components: Ignoring or misdiagnosing other transmission components, such as the solenoid valves or engine control module (PCM), can result in missing the real cause of the problem.
- Lack of necessary equipment or knowledge: Lack of specialized equipment or knowledge of the transmission control system may prevent accurate diagnosis and repair.
To successfully diagnose a P0991 code, you must have the correct equipment, experience, and knowledge of the transmission control system. It is important to follow the sequence of diagnostic steps and ensure that test results are interpreted correctly.
How serious is the fault code? P0991?
Trouble code P0991 indicates a problem with the transmission fluid pressure sensor, which can have serious consequences on the vehicle's performance. It is important to understand that transmission operation is key to the proper functioning of the vehicle, so any problems with transmission fluid pressure can lead to unpredictable transmission behavior, poor transmission performance, and even damage to transmission components. In some cases, the P0991 code may cause the following:
- Incorrect gear shifting: Problems with transmission fluid pressure can cause the transmission to shift incorrectly or even lock up the transmission.
- Increased wear on transmission components: If transmission fluid pressure is insufficient, transmission components may be subject to additional wear due to improper lubrication and cooling.
- Increased fuel consumption: Improper transmission operation can result in increased fuel consumption due to ineffective gears and additional stress on the engine.
- Potential safety hazards: Severe transmission problems caused by insufficient transmission fluid pressure may result in loss of vehicle control, which could pose a hazard to the driver and passengers.
Therefore, the P0991 code should be considered serious and it is recommended that immediate steps be taken to diagnose and correct the problem to avoid further damage and ensure safe operation of the vehicle.
What repair will help eliminate the code? P0991?
Resolving the P0991 trouble code depends on the specific cause of the code, there are several possible repair steps:
- Replacing or repairing the transmission fluid pressure sensor: If the cause of the P0991 code is a problem with the pressure sensor itself, it will need to be replaced. In case the problem is with the wiring or connections, they can be repaired or replaced.
- Checking and replacing transmission fluid: If the level or quality of the transmission fluid does not meet the manufacturer's recommendations, it is necessary to replace it and ensure that the pressure level is correct.
- Diagnostics and repair of the hydraulic transmission system: In some cases, the problem may be related to other components of the transmission hydraulic system, such as the solenoid valves or control module. It is necessary to carry out additional diagnostics and, if necessary, replace or repair these components.
- Checking and cleaning the transmission filter: A clogged or dirty transmission filter can also lead to transmission fluid pressure problems. Check the condition of the filter and, if necessary, replace or clean it.
- Software update: Sometimes the problem may be related to the transmission control module software. Check for firmware updates and install them if necessary.
It is important to note that a combination of different repair measures may be required to successfully resolve the P0991 code problem. If you are unsure of your skills or do not have the necessary equipment, it is recommended that you contact a qualified auto mechanic or certified auto repair shop.
P0991 ā Brand-specific information
Due to differences in diagnostic systems and components of different brands of vehicles, fault codes may have different meanings. Decoding code P0991 for some popular car brands:
- Toyota / Lexus: Transmission fluid pressure sensor/switch "E" circuit is intermittent/erratic.
- Ford: Transmission fluid pressure sensor/switch "E" circuit is intermittent/erratic.
- Chevrolet / GMC: Intermittent or unstable signal from transmission fluid pressure sensor āEā.
- Honda/Acura: Problems with the transmission fluid pressure sensor "E" or its control circuit.
- BMW: Transmission fluid pressure sensor/switch "E" circuit is intermittent/erratic.
- Mercedes Benz: Transmission fluid pressure sensor/switch "E" circuit is intermittent/erratic.
- Volkswagen / Audi: Intermittent signal from transmission fluid pressure sensor āEā.
- Subaru: Transmission fluid pressure sensor/switch "E" circuit is intermittent/erratic.
Please check the service documentation for your specific vehicle make and model as the code may vary slightly depending on the manufacturer.
