Diagnostic code **P1720** on vehicles of the brand Nissan indicates a serious malfunction in the transmission control system, namely a malfunction of the output speed sensor circuit. When you see this code on the scanner, it means that the electronic control unit (ECU) has stopped receiving correct data about how fast the wheels or transmission shafts are rotating. Without this information, the automatic transmission cannot calculate the correct gear shift timing, which leads to jerking, kicking and going into limp mode.
Many owners Nissan Qashqai, X-Trail or Teana encounter this problem suddenly: first the car starts to jerk when shifting from first to second gear, and then the Check Engine light comes on. Ignoring code P1720 is unacceptable, as this can lead to critical wear of the clutches or complete failure of the valve body. In this article we will look at how to accurately determine the cause of the breakdown, check the sensor and restore normal operation of the transmission without extra costs.
The essence of the problem and the mechanism of the error
Code P1720 stands for "Turbine Speed ββSensor A Circuit". In modern cars Nissan two main speed sensors are used: input (turbine) and output. It is the output sensor that is responsible for monitoring the rotation speed of the transmission output shaft, which allows the ECU to determine the current gear and vehicle speed. If the signal disappears or becomes illogical compared to the data from other sensors, the system records an error.
There can be several reasons for this situation, and they range from trivial to complex. Most often, the problem lies in the sensor itself, which over time loses its magnetic properties or becomes contaminated with metal shavings. Also, do not rule out broken wiring, oxidation of contacts in the connector, or a malfunction of the transmission controller (TCM) itself. It is important to understand that the error can be either permanent or appear only under certain operating conditions, for example, at high speeds or when the engine warms up.
For accurate diagnosis, it is necessary to understand exactly how the ECU checks this signal. The control unit constantly compares the readings of the input speed sensor, output speed sensor and throttle position sensor. If the calculated speed does not match the actual speed, or if the signal is interrupted for more than a certain time, an error occurs. In some cases, the problem may not be an electrical issue, but rather mechanical wear on the bearings or gears inside the transmission, causing a humming noise that the sensor perceives as noise.
Main symptoms and behavior of the car
The first sign of a problem is often not a light on the dashboard, but a change in the car's behavior. The driver may notice that gear shifting occurs with a delay, accompanied by strong shocks or jerks. In some cases, the gearbox may βfloatβ, that is, switch from one gear to another for no reason, even if the gas pedal is not pressed hard. These symptoms are especially noticeable in the urban driving cycle with frequent acceleration and braking.
A critical symptom is the transmission going into emergency mode. In this condition, the automatic transmission locks in one gear (usually second or third) or limits its shift range to prevent further damage. In this case, the engine may operate normally, but the car loses acceleration dynamics. The indicator may light up in the instrument cluster AT or Check Engine, and a message indicating a transmission malfunction will appear on the on-board computer display.
Sometimes the P1720 code only appears under certain conditions. For example, you may notice that the problem occurs only after a long trip, when the transmission is very warm, or vice versa, only when the oil is cold. It is also possible that an error may occur when driving on an uneven road, when vibration leads to a temporary break in the contact in the damaged wiring. If you notice such oddities, do not delay diagnosis, as driving in emergency mode can lead to overheating of the transmission oil and failure of the friction discs.
Diagnostics of the electrical circuit and sensor
The first step in eliminating the error is to visually inspect and check the electrical circuit. You need to locate the speed sensor, which is usually located on the transmission housing, closer to the rear axle or near the transfer case connection (for all-wheel drive models). Inspect the sensor connector for oxidation, moisture, or mechanical damage. Often the problem can be solved by simply cleaning the contacts and treating them with a special contact spray.
After a visual inspection, it is necessary to measure the resistance of the sensor with a multimeter. To do this, disconnect the connector and connect the probes of the device to the sensor contacts. The normal resistance value is usually in the range of 500 to 1500 ohms, but the exact numbers depend on the specific car model and year of manufacture. If the device shows infinity (open) or zero (short circuit), the sensor is faulty and requires replacement. Also check the integrity of the wires coming from the connector to the ECU for chafing or breakage.
| Validation parameter | Normal value | Fault value | Action |
|---|---|---|---|
| Sensor resistance | 800β1200 Ohm | Infinity or 0 Ohm | Replacing the sensor |
| Supply voltage | 5 Volt | 0 Volt or 12 Volt | Wiring check |
| Output signal | Alternating Current (AC) | Missing when rotating | Replacing a sensor or chip |
| Mass resistance | < 1 Ohm | High resistance | Mass cleaning |
Mechanical causes and internal defects
Sometimes the problem lies not in the electrics, but in the mechanical part of the transmission. The speed sensor reads information through a magnetic field created by a rotating disk with teeth or magnetic marks. If this disc is damaged, contaminated with metal shavings, or misaligned, the sensor will not be able to read the signal correctly. In cars Nissan With a variator (CVT), the problem may be related to wear on the cones or chain, which leads to unstable rotation speed of the shafts.
Particular attention should be paid to the condition of the oil in the transmission. If the oil is contaminated with wear debris, metal particles can settle on the speed sensor magnet, shielding its signal. In this case, simply cleaning the sensor and changing the oil may solve the problem without the need to purchase new parts. However, if there are a lot of chips in the oil, this may indicate deeper problems inside the box that require a major overhaul.
- Less than 50,000 km
- 50,000β100,000 km
- 100,000β150,000 km
- More than 150,000 km
If you suspect a mechanical problem, you will need to remove the sensor and carefully inspect the end of the sensor. There should be no large pieces of metal or dirt on the magnet. Also check whether the sensor itself has any play in the seat. If the seat is broken, the sensor may vibrate when the engine is running, causing the signal to be interrupted. In such cases, it may be necessary to replace the sensor along with the sealing ring or even repair the transmission housing.
Step-by-step instructions for replacing the sensor
Replacing the speed sensor is a procedure that you can do yourself if you have a minimum set of tools and access to a pit or lift. The process begins by de-energizing the car: remove the negative terminal from the battery to avoid a short circuit when disconnecting the connectors. Then locate the sensor on the gearbox housing and disconnect the electrical connector by pressing the latch.
Next, you need to unscrew the mounting bolt that holds the sensor in place. Be careful as the bolt may be very acidic. Use penetrating lubricant if necessary. After unscrewing the bolt, carefully remove the sensor, being careful not to damage the O-ring. If the ring remains in place or is damaged, it must be replaced with a new one to prevent moisture and dirt from entering the box.
βοΈ Preparing to replace the sensor
Installing a new sensor occurs in the reverse order. Insert the sensor into the seat as far as it will go, making sure that the O-ring is seated evenly. Tighten the mounting bolt to the recommended torque without over-tightening to avoid damaging the sensor housing. Connect the electrical connector until you hear a characteristic click. After completing the work, do not forget to connect the battery and reset the error using a scanner or by disconnecting the terminal for 10-15 minutes.
Before purchasing a new sensor, be sure to check its compatibility with your vehicle model and year, as connectors and parameters may vary even within the same Nissan model.
Error reset and adaptation after repair
After replacing the sensor or repairing the wiring, it is necessary to reset the stored error codes in the ECU memory. This can be done using a professional diagnostic scanner connected to the OBDII connector. From the scanner menu, select the "Error Reset" or "Clear DTC" function. If you don't have a scan tool, you can disconnect the negative terminal of the battery for 15-20 minutes, but this method is less reliable and may reset other vehicle systems, such as the clock or radio.
After resetting the errors, it is important to carry out the gearbox adaptation procedure. The ECU must re-learn the transmission operating parameters with new sensors. To do this, start the engine, warm up the transmission to operating temperature and drive the car in quiet mode, allowing the transmission to shift through all gears. Avoid sudden acceleration and braking in the first 20-30 kilometers after repair. This will help the system correctly adjust gear shift points.
What should I do if the error is returned immediately?
If P1720 returns immediately after a reset, it indicates that the problem has not been completely resolved. Possible causes: wire break inside the harness, ECU malfunction, mechanical damage to the sensor disk, or a poor-quality new sensor. In this case, it is necessary to conduct a more in-depth diagnosis with an oscilloscope.
Transmission prevention and maintenance
To avoid recurrence of the P1720 code, it is necessary to have the transmission serviced regularly. Timely replacement of transmission oil and filter is a key factor in the longevity of an automatic transmission. Contaminated oil not only impairs hydraulic performance, but also creates metal shavings that can damage sensors. Follow the manufacturer's instructions, which usually recommend replacement every 60,000 kilometers.
It is also recommended to periodically inspect the electrical connectors and wiring harnesses leading to the transmission. Vibration and temperature changes can lead to cracking of insulation and oxidation of contacts over time. If you notice signs of corrosion or damage, treat the contacts with a protective spray and replace the damaged sections of the wiring. Regular diagnostics on professional equipment will allow you to identify problems at an early stage, before they lead to expensive repairs.
Regular oil changes and electrical checks are the most effective way to prevent P1720 and extend the life of your vehicle's transmission.
β οΈ Attention: If P1720 is accompanied by loss of engine power or complete transmission failure, stop the vehicle immediately and call a tow truck. Continuing to drive can lead to irreversible damage to the transmission and increase the cost of repairs significantly.
β οΈ Attention: When purchasing a used speed sensor for Nissan, make sure it is in working order. Often used sensors have hidden defects that only appear under load, which will lead to repeated failure in a short time.
β οΈ Attention: Do not attempt to resolve P1720 by simply disconnecting the battery without correcting the physical cause. The ECU will remember the error and return it to memory after the first start, and in some cases it may block the operation of the transmission until the fault is eliminated.
Why does error P1720 only appear when it's hot?
When heated, materials expand, and if there are microcracks or poor contact in the wiring, they can open. Also, the magnetic properties of the sensor can change when overheated, which leads to signal loss. This requires careful inspection of insulation and contacts at engine operating temperature.
Is it possible to drive with error code P1720?
Driving is technically possible, but only in limited mode. The car will go into emergency mode, which will limit speed and dynamics. Long-term operation with this error is unacceptable, since incorrect gear shifts can quickly damage the clutches and valve body.
How much does it cost to replace a speed sensor on a Nissan?
The cost of a new original sensor varies from 2000 to 5000 rubles, depending on the model. An analogue from a third-party manufacturer can cost 2-3 times less. Replacement work in the service usually takes 30-60 minutes and costs from 1,500 to 3,000 rubles.
Does P1720 affect fuel consumption?
Yes, it is significant. Due to incorrect speed data, the ECU cannot select the optimal gear shift point, which leads to the engine operating in inefficient modes. Fuel consumption may increase by 10-20% compared to normal.
Is it necessary to change the ECU firmware during repair?
Usually not, if the cause of the error is eliminated physically (the sensor or wiring is replaced). However, in some cases, updating the ECU firmware can improve transmission algorithms and eliminate false alarms caused by software glitches.