P0722 Explained: Output Speed Sensor No Signal

Quick answer

• What it means: The powertrain control module (PCM) is not receiving a signal from the transmission's output speed sensor.
• Severity: Get it inspected soon. You can likely drive home, but the transmission may not shift correctly, leading to potential damage.
• Most common cause: A faulty output speed sensor.

What the P0722 code means

The official OBD-II definition for P0722 is "Output Speed Sensor Circuit No Signal." In plain English, this means the car's main computer, the PCM, has lost communication with the output speed sensor (OSS). This sensor is a critical component of your automatic transmission.

Your transmission has two speed sensors: an input speed sensor (ISS) and an output speed sensor (OSS). The ISS measures the speed of the transmission's input shaft, while the OSS measures the speed of the output shaft. The PCM compares the signals from both sensors to determine the gear ratio and to control when to shift gears. It also uses the OSS signal to display the vehicle's speed on your speedometer.

When the PCM detects that it's not receiving a signal from the OSS, it sets the P0722 trouble code and illuminates the Check Engine Light.

Common symptoms

You will likely notice significant drivability problems when the P0722 code is present. These can include:

• Check Engine Light is on
• Transmission may not shift gears properly or at all
• Harsh or erratic shifting
• Vehicle may enter "limp mode" (stuck in one gear)
• Inaccurate or non-functional speedometer
• Decreased fuel economy
• Engine stalling

Common causes

The causes for a P0722 code are usually related to the sensor itself or the wiring that connects it. Here are the most common causes, ranked from most to least likely:

1. Faulty output speed sensor: The sensor itself is the most common culprit. It can fail internally due to age or heat.
2. Wiring or connector issues: The wiring harness to the sensor can become damaged, corroded, or shorted. The connector can also become loose or filled with debris.
3. Contaminated transmission fluid: Dirty or low transmission fluid can interfere with the sensor's operation.
4. Tone ring problems: The OSS reads a toothed wheel called a tone ring. If this ring is damaged or has debris on it, the sensor cannot get a proper reading.
5. PCM issues: In rare cases, the powertrain control module itself may be faulty. This is the least likely cause and should be considered only after all other possibilities have been exhausted.

How a technician diagnoses it

A certified technician will follow a systematic process to diagnose a P0722 code. This ensures an accurate diagnosis and avoids unnecessary repairs.

1. Scan for codes: The first step is to connect a professional OBD-II scanner to the vehicle's diagnostic port. The technician will confirm the P0722 code is present and check for any other related codes.
2. Analyze freeze-frame data: The scanner will have captured a "snapshot" of the vehicle's sensor readings at the moment the code was set. This data provides valuable clues about the conditions under which the fault occurred.
3. Inspect the wiring and connector: The technician will perform a thorough visual inspection of the output speed sensor's wiring harness and connector. They will look for any signs of damage, corrosion, or loose connections.
4. Test the sensor: Using a digital multimeter (DMM) or a scan tool, the technician will test the sensor's signal. A good sensor should produce a voltage signal that changes with the vehicle's speed. If there is no signal, the sensor is likely bad.
5. Check the tone ring: If the sensor and wiring appear to be in good condition, the technician will inspect the tone ring for damage or debris. This may require removing the sensor from the transmission.
6. Test the PCM: If all other components check out, the technician may need to perform advanced diagnostics to test the PCM. This is a complex process and is usually reserved as a last resort.

Typical repair cost

The cost to repair a P0722 code can vary depending on the vehicle and the specific cause. Here are some typical cost ranges:

• Output speed sensor replacement: $150–$400 (parts and labor)
• Wiring repair: $100–$300
• Transmission fluid flush: $150–$250
• PCM replacement: $800–$2000+

Can I keep driving with this code?

It is not recommended to continue driving with a P0722 code. While you may be able to drive the vehicle, the transmission will not be shifting correctly. This can lead to further transmission damage, which can be very expensive to repair. If your vehicle is in limp mode, your speed will be limited, which can be a safety hazard.

Related codes

Several other codes are related to the P0722 code, as they all involve the transmission speed sensors or their circuits:

• P0720: Output Speed Sensor Circuit Malfunction
• P0721: Output Speed Sensor Range/Performance
• P0723: Output Speed Sensor Intermittent
• P0715: Input/Turbine Speed Sensor "A" Circuit
• P0717: Input/Turbine Speed Sensor "A" Circuit No Signal

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