Nissan Error P1720: Complete Diagnostic and Repair Guide

Error P1720 on cars Nissan is one of the most common problems that owners encounter when the Check Engine Light appears. This trouble code indicates a malfunction in the Vehicle Speed ​​Sensor (VSS) circuit, which critically affects the operation of the automatic transmission. When the transmission control module (TCM) no longer receives correct speed data, the vehicle goes into limp mode, limiting the number of gears and reducing dynamics.

Ignoring this problem can lead to serious damage to the valve body and clutches, since the system cannot correctly calculate switching points and oil pressure. You need to quickly diagnose it to avoid costly major repairs. In the article we will analyze all the nuances of the appearance of the code, methods for checking components and step-by-step instructions for troubleshooting.

The essence of the malfunction and the principle of operation of the system

Code P1720 in technical documentation Nissan stands for "Vehicle speed signal is missing or unstable." This means that the electronic transmission control unit does not see impulses from the sensor, or the signal is intermittent and does not correspond to the physical parameters of movement. The system records the discrepancy between the speed sensor data and the calculated values ​​​​obtained from the rotation sensors of the primary and secondary shafts.

In modern models such as Qashqai or X-Trail, the speed sensor is usually mounted on the transmission housing and senses the rotation of the output shaft. The received data is processed in real time, allowing the computer to determine the optimal gear shift time. If communication is interrupted, the TCM loses the ability to control the solenoids, resulting in harsh jolts or completely blocked upshifts.

It is important to understand that the problem does not always lie in the sensor itself. Often the cause lies in the wiring, connectors, or even mechanical wear on the ring gear that rotates the sensor. Incorrect signal may be caused by either electrical failure or physical damage to components. Without accurate diagnostics, replacing parts blindly often does not bring results.

Typical vehicle symptoms and behavior

When an error occurs P1720, the driver immediately notices a change in the car's behavior. The most obvious sign is the Check Engine light on your dashboard coming on. However, this is not the only symptom that should alert the owner. Nissan. The behavior of the car changes dramatically, turning from a comfortable vehicle into an uncontrollable object.

The so-called “emergency mode” of the gearbox is often observed. The car gets stuck in second or third gear, unwilling to shift up, no matter how hard you press the gas. Acceleration becomes sluggish and the engine runs at high speeds, creating increased noise and fuel consumption. In some cases, the transmission may not shift from first gear at all, which makes driving on the highway impossible.

In addition to problems with transmissions, the following manifestations are possible:

• 🚫 Complete absence of speed indication on the speedometer
• 🚫 Sharp jerks and impacts when trying to change gears
• 🚫 Engine braking does not work correctly or is missing
• 🚫 The car may stall when stopping at a traffic light due to incorrect load data

Sometimes the error appears only under certain conditions, for example, when driving on uneven roads or in severe frost. This indicates a problem with contacts or wiring that reacts to vibration or thermal expansion. If you notice at least one of these signs, you need to contact a specialist as soon as possible.

Common Causes of Code P1720

Reasons for the error P1720 there may be several, and they range from simple electrical problems to serious mechanical failures. The most common reason is failure of the speed sensor itself. Over time, the magnet inside the sensor loses its properties, or the electronic element inside the housing is destroyed by moisture and vibration.

The second most common factor is a violation of the integrity of the wiring. Wiring harnesses in the engine compartment and under the car are exposed to constant influences: temperature changes, oil, reagents and mechanical damage. Open circuit or a short circuit to ground leads to the fact that the signal simply does not reach the control unit.

It is also worth paying attention to the following possible reasons:

• 🔧 Oxidation or contamination of contacts in the sensor connector
• 🔧 Damage to the ring gear (gearbox) that rotates the sensor
• 🔧 Malfunction of the transmission control module (TCM) or its software
• 🔧 Problems with grounding (ground) of the control unit

⚠️ Attention: In some cases, the P1720 error may be false and occur due to low transmission fluid levels. Check the transmission dipstick before attempting any complex electrical work.

Diagnostics and testing of components

The first step in eliminating the error is to scan the system with professional diagnostic equipment. You need to not only read the code, but also view the speed sensor parameters in real time. By connecting the scanner, you will see whether the speed values ​​​​change as the car moves. If the value is always zero, the problem is obvious.

Visual inspection is critical. You need to remove the connector from the speed sensor and check it for oxides, dirt or traces of oil. Contacts must be clean and tight. Check the integrity of the wiring harness along its entire length, paying attention to places where there are bends and friction on body elements.

To accurately check the sensor itself, you will need a multimeter. You need to measure the sensor resistance and check for supply voltage.

• 🛠️ The sensor resistance must be in the range specified in the technical documentation (usually 200-500 Ohm)
• 🛠️ Check the 5V or 12V voltage supply (depending on the model) to the power contacts
• 🛠️ Check the ground wire for a break to the car body

Step-by-step instructions for replacing the sensor

If the diagnostics showed a malfunction of the sensor itself, it must be replaced. The replacement process is relatively simple, but requires care, since the sensor is located in a hard-to-reach place. Before starting work, be sure to turn off the power to the car by disconnecting the battery terminal.

To work you will need a set of wrenches, a multimeter and a new speed sensor. Follow this checklist for a successful replacement:

First, locate the sensor on the transmission housing. It is usually located on top, near the speedometer cable attachment point (on older models) or in the differential area. Carefully disconnect the electrical connector by pressing the latch. Unscrew the mounting bolt and remove the old sensor.

Installing a new sensor is done in the reverse order. Pay attention to the condition of the O-ring: if it is worn out, oil may begin to leak, which will lead to new problems. After installation, be sure to clear errors through the diagnostic scanner and conduct a test drive.

⚠️ Attention: When installing a new sensor, do not overtighten the mounting bolt. The sensor body is made of plastic or soft metal and can crack under excessive force, causing it to fail.

Complex cases and wiring repairs

Sometimes replacing the sensor does not help, and the error P1720 returns. In this case, the problem lies deeper - in the wiring or the control unit itself. You need to check the continuity of the wires from the sensor connector to the TCM connector. This is a time-consuming procedure that requires a wiring diagram for your vehicle.

Often a wire break occurs inside the insulation, but it is not visually noticeable. Use a multimeter in continuity mode to test each wire individually. Pay special attention to the places where the harness passes through the body panels or bends at the engine. Vibration over time leads to breaking of copper strands.

If the wiring is good and there is still no signal, the problem may be in the transmission control unit itself. In rare cases, failure of the TCM's internal circuits will result in the signal being unable to be read. In such a situation, the unit will need to be reflashed or replaced with a new or restored one.

What to do if the error does not clear?

If after replacing the sensor and checking the wiring the error does not disappear, try disconnecting the battery for 15-20 minutes. Sometimes the control unit needs a complete power reset. If this does not help, the problem may be a software glitch and a visit to the dealership will be required to reflash the TCM.

Prevention and Maintenance

To avoid the error reappearing P1720, the transmission must be serviced regularly. Timely replacement of transmission fluid and filters will help maintain normal pressure in the system and prevent overheating of components. Dirty oil can clog the valve body channels, which indirectly affects the operation of the sensors.

It is also recommended to periodically inspect electrical connectors for the presence of oxides. If you notice moisture or oil in the connector, clean it with a special contact cleaner and apply a conductive lubricant. This will protect the contacts from corrosion and ensure reliable contact.

Important tips for extending system life:

• 🛡️ Avoid sudden starts and extreme loads on the transmission
• 🛡️ Monitor the oil level in the gearbox and top it up on time
• 🛡️ Check the condition of protective wiring covers

Model Nissan	Gearbox type	Common cause P1720	Recommended Action
Qashqai (J10, J11)	CVT / automatic transmission	Speed sensor wear	Replacing the sensor
X-Trail (T31, T32)	CVT	Wiring problems	Checking the wiring harness
Teana (J31, J32)	Automatic transmission Jatco	Oxidation of contacts	Cleaning the connector
Almera (N16, N15)	Automatic transmission	TCM malfunction	Block diagnostics

Remember that timely diagnosis - the key to the long life of your car. Ignoring transmission errors can turn a simple sensor repair into replacing the entire transmission. Error P1720 requires immediate attention, as it directly affects the driving safety and handling of the vehicle. Do not delay your visit to service when the first signs of a malfunction appear.

FAQ: Frequently asked questions

Is it possible to drive with error code P1720?

It is not recommended to drive with this error, as the car goes into emergency mode. This limits speed and dynamics, which can be dangerous when overtaking or driving in traffic. In addition, long-term operation in emergency mode can damage the gearbox clutches.

How much does it cost to replace a speed sensor on a Nissan?

The cost depends on the car model and region. The sensor itself is relatively inexpensive, but the work of replacing it can vary from 1,500 to 5,000 rubles. On some models, access to the sensor is difficult, which increases the cost of work.

Will resetting errors without repair help?

Resetting errors through a scanner or disconnecting the battery will only give a temporary effect. If the fault is physical (broken sensor or broken wire), the error will return immediately after several ignition cycles. Repairs should be aimed at eliminating the cause, not the effect.

How often does the speed sensor fail?

Speed sensors are reliable components and typically last the life of the vehicle. However, under conditions of aggressive use, bad roads and temperature changes, they can fail after a mileage of 100-150 thousand kilometers. Regularly checking the condition of the wiring extends its service life.