P0791 - OBD Trouble Code

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This OBD error P0791 is a generic trouble code and shows that there is an issue with the transmission intermediate shaft speed sensor circuit. This circuit is responsible for relaying shaft speed data to the PCM or Powertrain Control Module. Basically, the intermediate shaft speed is supposed to slowly increase until the shift point. However, if the PCM notes that it isn’t increasing slowly, then the shift strategy can’t be determined correctly and go ahead and store error code P0791. Also, if the PCM receives no signal, or a haphazard signal from the shaft speed sensor, it will set this OBD trouble code.

The Transmission Control Module comes to know about how fast the intermediate shaft of the transmission is spinning from the intermediate shaft speed sensor. This is done so that right gear can be engaged when needed by the driver. When an inaccurate signal from the sensor is received by the Transmission Control Module or TCM, then it is unable to properly shift the vehicle from gear to gear as per requirement. The vehicle will always need a change of gear depending on the rate of acceleration desired by the driver. The PCM or TCM will hence set the P0791 code.

What causes this problem with the Intermediate Shaft Speed Sensor A Circuit?

• Malfunction of the intermediate shaft speed sensor
• Malfunction of the input speed sensor
• Malfunction of the output speed sensor
• Defect in the shift solenoids
• Contaminated automatic transmission fluid
• Malfunction in the engine temperature sensors, or even other drivability sensors
• Defect or damage of the electrical components, like wires and connectors
• In rare cases, a malfunction of the PCM

1. Shaft Speed Sensor - If the P0791 code is still flashing, Check for repairs in the sensor otherwise replace it with Parts Avatar online. You can order from the comfort of your home and have it delivered to your doorstep.
2. Input and Output Speed Sensor - Try to repair the issues, if that’s not resolving the issue you will have to replace it. We have a wide range of car parts that you can order. Simply check the compatibility as per your vehicle and order easily.
3. Transmission Fluid - Check for contaminants and replace the fluid or refill it to the level needed if it’s not on the optimum level. This way you can easily resolve code P0791. You can easily pick one up from the Parts Avatar warehouses located across Toronto.
4. Transmission Wires And Connectors - depending on the condition of the wires and connectors, you will have to repair them, if that’s not helping, order online at Parts Avatar. We have a wide range of branded aftermarket car parts.
5. Powertrain Control Module - The PCM is a crucial part of your vehicle, you can repair it or opt for replacement with us. We offer free shipping across Canada for orders over CAD $99.

It is vital to know the symptoms of an issue as only then you would be able to solve the problem. So that’s why we have listed out some major symptoms of OBD Code P0791 here:

Common Symptoms

You will notice the check engine light is illuminated when this code is set. The car will also experience transmission problems like; harsh shifting or inability to shift. You may also note engine performance problems, including stalling or throttle hesitation, even frequent engine misfires may be observed along with reduced fuel efficiency. The speedometer may also fair or act erratic, this is also a common symptom. In very rare scenarios, drivability issues may also arise.

Want to correct the Trouble Code P0791? Read these easy correction steps.

• Replace the intermediate shaft speed sensor
• Replace input speed sensor
• Replace output speed sensor
• Replace shift solenoids
• Replace electrical components
• Replace or add transmission fluid to the level required
• Replace drivability sensors
• Replace PCM

Parts Avatar Canada is here to solve all your issues related to car parts. We have stocked a wide range of best priced Shaft Speed Sensor, Input Speed Sensor, Output Speed Sensor, Transmission Fluid, Wires and Connectors, Power Control Module and a lot more to help you out in fixing your car.

It is essential to diagnose this fault code. Here are some steps which a mechanic should follow for diagnosing the problem that triggered a P0791 code to be stored:

• This code is diagnoses with the help of a standard OBD-II trouble code scanner. It is simply connected to the diagnostic post of the vehicle and all information is recorded and the data is free framed.
• Any additional trouble codes will also have to be recorded and addressed depending on the order of their occurrence. After they are noted, the codes are cleared and the vehicle is taken for a test drive to see if it resets or the PCM enters readiness mode. If the code is not immediately set it is be because there is an intermittent issue, or that the code was triggered incorrectly.
• If the code immediately resets, then a visual inspection of the systems electrical components is in order.
• All the damaged wires or connectors will have to be repaired and replaced as per need. If the damage has occurred to due a failure of another component, then that should be immediately addressed. After that, the transmission fuel should be checked to ensure it’s clean and on sufficient level.
• The nest check to be done is of the intermediate shaft speed sensors reference voltage and ground signals. The digital volt/ohm meter or DVOM is used to check continuity in circuits, any discrepancies noticed in relation to the ones prescribed by the manufacturer will have to be replaced.
• Now, it’s time to check the input and output sensors, also the shift solenoids. Upon inspection is no problems have been noticed, then an oscilloscope will have to be used in-order to gather information from the transmission intermediate shaft speed sensor.
• Once any component is replaced during the process of the diagnosis the codes should once again be reset, and the vehicle should be restarted to check if the code returns. This will give the assurance that the problem has indeed been fixed.

Common Mistakes When Diagnosing the P0791 Code

• Not following the OBD-II trouble code diagnosis protocol correctly
• Speed sensor is replaced when there’s no need