P077A OBD Error Code: Problem & Solutions

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Do you experience a direction signal loss in your vehicle? Do you often see the P077A error code? The fastness of the output shaft is informed to the TCM by the output speed sensor so that it can verify as to which gear is correctly involved. If the transmission control module finds an irregular signal from these sensors, then the engine control module or the hybrid control module will set the P077A error code.

The speed sensor will emit a pulse signal once it identifies the revolution of the idler gear parking pawl lock gear. This pulse signal is then sent to the transmission control module which is finally converted into vehicle speed.

What causes this problem with the Output Speed Sensor Circuit - Loss of Direction Signal?

• The output speed sensor is damaged.
• The output speed sensor has metal rubbles.
• The output speed sensor has shorted circuits or opened connectors.
• The reluctor ring is broken or worn out.
• The transmission has mechanical failures.

1. Speed Sensor - Check for this component if they are damaged or broken. If they are defective replace them with the right one.
2. Connectors - Check for the terminals of connectors and see if they are damaged or broken. Replace the faulty connectors to avoid P077A error code.
3. Transmission Control Module - Avoid the P077A error code in your vehicle by replacing the faulty transmission control module.
4. Speedometer/Odometer - The speedometer has to function correctly to show proper readings. Replace them if they malfunction.

If you are facing OBD error code P077A, then there are significant common symptoms that can be felt or observed. We have worked out a list here to help you out in understanding this problem better.

Common Symptoms

• The speedometer or odometer operates irregularly.
• Shift patterns of the transmission is abnormal.
• The transmission slips at times or there is delayed involvement.
• The traction control system activates or deactivates.
• There may be presence of other transmission and ABS codes stored.

It is very important to fix the fault code P077A. So here are some ways with which you can correct this issue:

• Replacing the speed sensors.
• Changing the fuel injectors.
• Fixing the reluctor rings.

Apart from the fuel injector, you might need to undergo few more replacements. You might need Speed Sensor, Connectors, Transmission Control Module, Speedometer/Odometer and many other parts. Where to get them from? Well, if you want quality parts, then we can prove to be your dream destination.

If you want to easily diagnose this fault code, then all you have to do is to follow the steps which are mentioned below:

• Once the sensor is removed you have to inspect the reluctor ring. You may end up in trouble if the component is damaged, broken or misses any teeth. Check for other transmission related symptoms in your automatic transmission fluid as they must be clean. If the fluid is less than 0ne quarter, refill them and check for leaks. The transmission must be full and in proper mechanical connection before further diagnosis.
• In order to diagnose the P077A error code you need a diagnostic scanner with oscilloscope, DVOM, and a trustable source of information.
• Connect the scanner to the vehicle and retrieve all codes and freeze frame data. You can also note down the information as it can help in further diagnosis.
• Search for the apt technical service bulletin which matches with the symptoms and stored error codes as they can help you in the right and speed diagnosis.
• As you test drive the vehicle, use the scanner data stream to notice the output speed. If you narrow down the data stream to show only specific fields, then it will increase the speed and exactness of the data delivery. Varying or irregular signals from the input or output speed sensor will lead to cable or sensor problems.
• Carry out a resistance test with a DVOM while you disconnect the output speed sensor. Your vehicle source information will have wiring diagrams, connector views, connector pinout charts and manufacturer’s preferred testing process. You will find failures if the output speed sensor does not match with the manufacturer’s specification.
• Use the oscilloscope to obtain live data from the output speed sensor. Inspect both the output speed sensor signal wire and ground wire. In order to perform this test, you have to lift your vehicle. Once your vehicle is secure and the wheels are safely lifted from the ground, you have to run up the drivetrain so that you can see the waveform pattern in the oscilloscope. Look for malfunctions or variations in the waveform.
• Disconnect the connectors and every of its related controllers while you perform circuit resistance and continuity test with the help of a DVOM. If you fail to do so, then it may result in damaging the controller.

Common Mistakes When Diagnosing the P077A Code

• The control module fails due to high voltage.
• Failure of the output shaft speed sensor.
• Faulty transmission control module.
• Cable issues.

P077B - Output Speed Sensor Circuit - Direction Error