When faced with an illuminated Check Engine light on the dashboard of your Nissan, owners often try to find a solution to the error code on the Internet. One of the most common and scary codes for Japanese car owners is P1720. This failure is directly related to the operation of the automatic transmission and can significantly limit the vehicle's ability to move.
Ignoring this signal is unacceptable, since the transmission control system may go into emergency mode, blocking gear shifting. As a result, the car loses dynamics, fuel consumption increases and there is a risk of damage to internal components. automatic transmission. In this article we will look in detail at what exactly the code means P1720, what causes it and how to fix the problem yourself or at a service center.
The essence of the malfunction and the purpose of the sensor
Error code P1720 stands for “No Vehicle Speed Signal” or “Invalid Transmission Output Speed Sensor Signal.” The electronic control unit (ECU) constantly monitors the speed of rotation of the secondary shaft automatic transmission. This information is critical for calculating gear shift timing and valve body control.
If the computer does not receive a signal from the sensor within a certain time, and the engine continues to run, it detects a failure and records an error. Without speed data, the transmission cannot correctly determine when to shift into the next gear. This leads to the fact that the box “thinks” that the car is standing still, although the wheels are actually spinning.
In modern models Nissansuch as Qashqai or X-Trail, this sensor is often integrated into the hydraulic control unit. It is part of the system responsible for smooth switching. The absence of a signal makes it impossible for the control algorithms to work, which forces the computer to turn on the “Limp Home” mode (emergency mode).
⚠️ Warning: When P1720 occurs, the transmission may become stuck in one gear (usually 2nd or 3rd) and will not shift. Prolonged driving in this mode with high engine speeds can lead to overheating of the oil in the automatic transmission.
Typical symptoms of failure
Understand that the problem is in the code P1720, it is possible not only by the scanner, but also by the behavior of the car on the road. The most striking sign is a sharp change in acceleration dynamics. The car may start to jerk, and the gas pedal stops responding the way you are used to. Gear changes become harsh or disappear altogether.
Often, owners notice that the speedometer on the dashboard shows zero or begins to “jump” randomly. This happens because the speed readings are taken precisely from the sensor that has failed. In some cases, the error is accompanied by the indicator lighting up AT or engine malfunction icon.
- 🚗 A sharp drop in power and the inability to accelerate above 40-60 km/h.
- 🛑 Locking gear shifting into one fixed mode.
- 📉 Unpredictable jumps in speedometer readings when driving.
It is important to note that sometimes the error may only appear under certain conditions, such as after the engine has warmed up or when driving on uneven roads. This may indicate a broken wiring, which occurs due to vibration or expansion of materials when heated. Therefore, diagnosis must be comprehensive.
Common Causes of Code P1720
The most common cause of the error is P1720 is a physical failure of the speed sensor (Output Speed Sensor). Over time, the magnet inside the sensor can weaken and the electronics can degrade. Under aggressive operating conditions, with temperature changes and vibrations, the service life of the sensor is reduced and it stops generating the correct signal.
The second common reason is wiring problems. The wiring harness leading to the transmission is constantly exposed to dirt, moisture and high temperatures. The insulation may fray, the contacts may oxidize, or the connector may simply come off. This leads to an open circuit or short circuit, which prevents the signal from reaching the ECU.
Sometimes the problem lies not in the electrics, but in the mechanics of the gearbox. If inside torque converter or on the shaft where the sensor is installed, tooth destruction or loss of magnetic properties has occurred, the sensor simply will not see rotation. In such cases, replacing the sensor itself will not help; repair of the valve body or transmission will be required.
- 🔌 Oxidation or corrosion of contacts in the sensor connector.
- 🔧 Mechanical damage to the wire due to vibration or friction.
- 🔩 Wear of internal automatic transmission components that affect speed reading.
It is also worth considering that in some cases the error may be false and caused by a failure of the control unit software. This is more common on older models Nissan with outdated firmware. A software update can solve the problem without replacing expensive parts.
- Check Engine light came on
- Speedometer shows 0
- Automatic transmission stopped shifting
- The engine stalls while driving
Diagnostics and testing of the electrical circuit
The first step when you find an error is P1720 should be a visual check of the speed sensor connector. It is usually located on the top or side of the transmission. You need to find it, disconnect it and carefully inspect the contacts. The presence of green deposits, dirt or moisture will immediately indicate the cause of the failure.
If everything is visually clean, you need to check the integrity of the wires with a multimeter. You will need to test the circuit from the sensor connector to the ECU connector. A break or high resistance in the wire will indicate the need to replace the harness or repair the wiring. Wires often fray at places where they are bent or attached to the body.
Checking the sensor itself is also possible using a multimeter. It is necessary to measure the resistance between the sensor contacts. Normal values are usually in the range from 200 to 1500 ohms (depending on the car model). If the device shows “infinity” or zero, the sensor is faulty and requires replacement.
⚠️ Attention: Before starting any work on the electrical part of the automatic transmission, be sure to disconnect the negative terminal of the battery. A short circuit in the transmission control circuit can damage an expensive electronic control unit.
☑️ Speed sensor circuit diagnostics
Speed Sensor Replacement Procedure
If diagnostics confirm a malfunction of the device itself, it will need to be replaced. To do this, you need to raise the car on a lift or pit to gain access to the bottom of the transmission. The sensor is usually attached with a single bolt and has an electrical connector that is easily disconnected.
The replacement process does not require complex dismantling of units. Simply unscrew the mounting bolt and carefully remove the old sensor. It is important not to damage the O-ring so that oil does not start leaking from the seat. Before installing a new element, it is worth lubricating its seal with clean automatic transmission oil.
After installing the new sensor and connecting the connector, you need to reset the error through the diagnostic scanner. You should then take it for a test drive, checking to see if the symptoms go away and if the speedometer is working correctly. If the error returns immediately, then the problem is deeper and may be related to the wiring or mechanics.
- 🔧 Use original spare parts or high-quality analogues to ensure accurate readings.
- 🛢️ Check the oil level in the box before starting work, as some of the liquid may leak out.
- 🔨 Clean the seat from dirt and carbon deposits before installing a new sensor.
Features of replacement on different Nissan models
On models with a variator transmission (CVT), the speed sensor is often part of the module, and replacing it may require removing the automatic transmission pan. On classic machines (for example, Jatco), the sensor is located separately and is easier to change.
In some cases, the ECU “remembers” the old operating parameters. Resetting adaptations through dealer equipment can speed up the normalization of the transmission.
Replacing the speed sensor is the most common and cost-effective way to resolve the P1720 code and will solve the problem in 80% of cases if the wiring is good.
Compatibility table and common models
Error P1720 found on a wide range of vehicles Nissanequipped with automatic transmissions. Below is a table showing the frequency of this error on popular models and typical sensor locations.
| Model Nissan | Transmission type | Error rate | Location Features |
|---|---|---|---|
| Nissan Qashqai | CVT / 4AT | High | On the side of the valve body |
| Nissan X-Trail | CVT / 4AT | Average | On the top gearbox cover |
| Nissan Teana | 4AT / 6AT | Average | Inside the pan (removal required) |
| Nissan Pathfinder | 4AT | Low | From the side, access through protection |
| Nissan Patrol | 4AT / 5AT | Low | On the back of the case |
As can be seen from the table, on crossovers Qashqai and X-Trail The problem occurs most often due to specific operating conditions and design features of the transmission. On large SUVs such as Patrol sensors are more secure and reliable.
Repair costs and prevention tips
The price of the speed sensor itself varies depending on the car model and the manufacturer of the spare part. The original can cost from 3,000 to 8,000 rubles, while high-quality analogues are offered for 1,500–2,500 rubles. Replacement work at a service station usually takes about 30-60 minutes and is inexpensive.
To avoid reoccurrence of the error, it is recommended to regularly check the condition of the wiring and connectors. It is also important to monitor the level and condition of the oil in the gearbox. Dirty oil with metal shavings can clog the valve body channels and damage the sensor from the inside.
Do not delay diagnostics when the first signs of a failure appear. Driving with a faulty transmission control system can lead to more serious damage, the repair of which will cost many times more. Regular maintenance is the key to the long life of your car.
⚠️ Attention: If you replaced the sensor, but the error returned after a couple of days, most likely the problem is not in it, but in the wiring or the internal state of the valve body. In this case, an in-depth diagnosis from an automatic transmission specialist is necessary.
When purchasing a new sensor, be sure to check the part number with the number on the old sensor, as visually similar parts may have different calibration and resistance.
Frequently asked questions (FAQ)
Is it possible to drive with error code P1720?
Technically possible, but highly undesirable. The car will go into emergency mode, lose dynamics and will not be able to change gears. This creates danger on the road, especially when overtaking or driving uphill.
Does P1720 reset itself after replacing the sensor?
No, the error is stored in the ECU memory. It must be reset using a diagnostic scanner after replacing the faulty part and eliminating the causes of the failure.
Does P1720 affect the operation of the air conditioner?
In some cases, the ECU may turn off the air conditioning if vehicle speed data is incorrect to reduce the load on the engine in limp mode.
Which sensor is better to install: original or analogue?
It is recommended to install the original sensor or trusted brands (for example, Aisin or Hitachi). Cheap analogues may have inaccurate characteristics, which will lead to repeated failures.
Understanding the Nature of the Error P1720 allows owners Nissan act wisely and do not overpay for unnecessary repairs. Timely diagnostics and the use of high-quality spare parts guarantee reliable operation of the transmission for many years.