Error code P1123 on Nissan: a complete diagnostic and repair guide

Error P1123 - one of the most common problems in electronic engine control systems Nissan, especially on models with gasoline engines QR25DE, MR20DE And VQ35DE. This code indicates a malfunction in the throttle control circuit, but its appearance can be associated with a dozen different reasons - from simple contamination to serious breakdowns ECU. Unlike errors like P0300 (misfires), which immediately make it clear that there is an ignition problem, P1123 often disguised as other symptoms: floating speed, jerking during acceleration, or even a complete loss of power.

Owners Nissan Qashqai, X-Trail And Teana encounter this error most often, but it can also appear on other models - from Almera to Pathfinder. The main difficulty is that Code P1123 is not always accompanied by the Check Engine light on the dashboard, especially if the malfunction is intermittent. This means that a driver can drive for months with a problem, unaware of its existence, until the symptoms become critical.

In this article we will look at:

• 🔍 What exactly does error P1123 mean? and how it is deciphered for different models Nissan.
• ⚙️ Top 5 reasons for the appearance of the code, from the simplest to those requiring specialist intervention.
• 🛠️ Step-by-step diagnostic instructions with and without a scanner.
• 💰 Repair cost in the service vs self-removal.

What does error code P1123 mean on Nissan?

Code P1123 in the diagnostic system Nissan stands for "Throttle Position Sensor (TPS) Circuit Malfunction — Bank 1" (Throttle position sensor circuit fault, bank 1). Unlike universal codes (for example, P0171 - lean mixture), this code is specific to problems with electronic throttle control (ETCS — Electronic Throttle Control System).

In modern Nissan the throttle valve has no mechanical connection with the gas pedal - its position is regulated electronically based on signals from:

• 📡 Throttle Position Sensor (TPS) — sends data about the current opening angle.
• 📡 Accelerator Pedal Position Sensor (APP) — records the driver's press.
• 🖥️ Electronic control unit (ECU) — compares signals and adjusts the opening of the damper.

When ECU detects a discrepancy between the expected and actual position of the damper (for example, the damper is open at 20°, and the sensor shows 15°), it records an error P1123. It is important to understand that this code can be either primary (the problem is in the sensor itself) or secondary (a consequence of faulty wiring, damper, or even firmware ECU).

The main symptoms of error P1123

Error P1123 rarely manifests itself in the same way on different cars, but there are a number of common signs that should alert you:

• ⚡ Floating idle speed (from 500 to 1500 rpm without pressing the pedal).
• 🚗 Jerks during acceleration, especially at low and medium speeds (30–80 km/h).
• 🛑 Slow response to the gas pedal — the machine “stumbles” when pressed.
• 🔥 Sudden switch to emergency mode (rev limit to 2000–3000).
• 💡 Check Engine Lights On and Off Randomly (typical for periodic failures).

On Nissan Qashqai (especially with a motor MR20DE) the error is often accompanied by hard automatic transmission shifts, since ECU tries to compensate for unstable engine operation. On X-Trail with QR25DE may be observed detonation under hard acceleration - this is due to incorrect calculation of the fuel mixture due to failures in the sensor data.

⚠️ Attention: If together with P1123 codes appear P0120 (TPS circuit malfunction) or P2135 (mismatch of TPS sensor signals), the problem is almost certainly in the sensor itself or its wiring. In this case, replacing the sensor solves the issue in 80% of cases.

Symptom	Probable Cause	Urgency of repair
Floating speed	Throttle contaminated or TPS faulty	Average
Jerks during acceleration	Wiring or ECU problems	High
Emergency mode	Critical TPS or throttle failure	Critical
Check Engine Flashing	Short circuit in the sensor circuit	High

Top 5 causes of error P1123 on Nissan

Based on repair statistics (data from services Nissan for 2020–2026), the most common causes of P1123:

1. Throttle valve contamination (45% of cases). Carbon deposits and oil entering through the crankcase ventilation system disrupt the smooth movement of the damper. This is especially true for engines with mileage >100 thousand km.
2. TPS sensor malfunction (30%). The sensor contacts wear out or the internal circuit breaks. On Nissan The original sensor often fails Hitachi (article 22680-4M000).
3. Wiring problems (15%). Oxidation of contacts in the sensor connector or broken wires (especially after repairs or an accident).
4. ECU firmware failure (7%). After updating the software or "rolling back" to a previous version, throttle calibration errors may occur.
5. Mechanical wear of the damper (3%). Cracks in the plastic housing or play in the damper shaft (typical for Nissan Note And Micra).

Interesting fact: on Nissan Juke with motor HR16DE error P1123 often appears after replacing the battery. This is due to the fact that ECU loses adaptive throttle settings and must be reset via diagnostic equipment (e.g. Consult-III or Launch X431).

How to diagnose error P1123 yourself

For diagnostics P1123 it is not necessary to go to a service center - a basic scanner is enough (for example, ELM327 with the program Torque Pro) and a multimeter. Here is a step-by-step algorithm:

1. Read error codes with a scanner (make sure there are no accompanying codes)

2. Visually inspect the throttle assembly for contamination

3. Check the voltage at the TPS sensor (there should be 5V between pins 1 and 2)

4. Measure the sensor resistance (between pins 2 and 3 - 1–5 kOhm when changing the damper position)

5. Check the circuit for open circuit (ring the wires from the sensor to the computer)

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Step 1: Read codes

Connect the scanner to the connector OBD-II (located under the steering wheel) and read all errors. If in addition P1123 there are codes P0100 (MAF sensor) or P0335 (crankshaft sensor), the problem may be complex. Remove errors and check if it returns P1123 after restarting the engine.

Step 2. Inspect the throttle assembly

Remove the air duct and inspect the damper. If black deposits or oil are visible on the walls, cleaning is necessary. Use a carburetor cleaner (eg LIQUI MOLY Pro-Line Drosselklappen-Reiniger). Do not use metal brushes - they damage the damper coating.

Step 3: Checking the TPS Sensor

Disconnect the sensor connector and check:

• 🔋 Supply voltage (between pins 1 and 2 on the harness connector) - should be 4.8–5.2V.
• 📉 Sensor signal (between contacts 2 and 3) - with the damper closed 0.3–0.7V, when open - 4–4.7V.
• 🔄 Smoothness of signal change — when the damper is slowly opened, the voltage should increase without surges.

⚠️ Attention: On some models Nissan (For example, Pathfinder R51) The TPS sensor is built into the throttle body and is not sold separately. In this case, you will have to change the assembly assembly (article no. 22680-4M01A).

How to Fix Error P1123: Step-by-Step Instructions

The repair method depends on the cause of the error. Below are instructions for the most common cases.

1. Cleaning the throttle body

You will need: throttle cleaner, rags, screwdriver.

1. Remove the air duct by disconnecting the clamps.
2. Apply cleaner to the valve and carefully remove carbon deposits. Don't rub too hard - this may damage the special coating.
3. Clean the air supply channel bypassing the damper (if any).
4. Reassemble everything in reverse order and reset the errors with the scanner.

2. Replacing the TPS sensor

You will need: a new sensor (for example, Hitachi 22680-4M000 for Qashqai J10), T20 screwdriver.

1. Disconnect the sensor connector.
2. Unscrew the 2 bolts securing the sensor to the throttle.
3. Install the new sensor and connect the connector.
4. Swipe throttle adaptation through the scanner (in the menu ETCS → Throttle Learning).

How to do throttle adaptation without a scanner?

On some models Nissan (For example, Almera N16) adaptation can be done manually:

1. Stop the engine and turn off the ignition for 10 seconds.

2. Turn on the ignition (without starting the engine) and wait 3 seconds.

3. Within 5 seconds, fully depress and release the gas pedal 5 times.

4. Wait 7 seconds, then press the pedal all the way down and hold for 20 seconds until the Check Engine light flashes.

5. Release the pedal and start the engine.

3. Wiring repair

If the problem is in the wires, proceed as follows:

• 🔍 Check the circuit from the TPS sensor to ECU (pin 49 on most models).
• 🔧 Strip and insulate damaged wires or replace the entire harness.
• 🛠️ Apply dielectric grease to the connector contacts.

The cost of repairs in the service vs on your own

Elimination prices P1123 vary depending on the reason and vehicle model. Below are indicative prices for Moscow/St. Petersburg (2026):

Type of work	Cost in service (₽)	Cost yourself (₽)	Notes
Diagnostics with a scanner	1 500–2 500	0 (if you have your own scanner)	Includes reading codes and checking parameters
Throttle cleaning	2 000–3 500	300–500 (cost of purifier)	Difficulty: ★☆☆
Replacing the TPS sensor	4 000–7 000	1,500–3,000 (sensor cost)	Difficulty: ★★☆
Replacing the throttle assembly	12 000–20 000	8,000–15,000 (node cost)	Difficulty: ★★★
Flashing the ECU	5 000–10 000	Not recommended on your own	Requires specialized software

Self-repair is beneficial if the problem is cleaning the damper or replacing the sensor. However, for working with ECU or wiring, it is better to contact a service center - errors here can lead to more serious damage (for example, failure of the control unit).

On Nissan X-Trail T32 with motor MR20DD Replacing the throttle assembly is more expensive due to its integration with the variable valve timing system. In this case, it is advisable to look for a used unit for disassembly (price ~5,000 ₽ versus 15,000 ₽ for a new one).

Frequently asked questions about error P1123

Is it possible to drive with error code P1123?

Short term - yes, but not recommended. Driving for a long time with this error leads to:

• 🔥 Increased fuel consumption (up to +20%).
• ⚙️ Accelerated wear of the catalyst due to the wrong mixture.
• 🚗 The risk of going into emergency mode at the most inopportune moment.

If the error appears for the first time, you can drive to your home or service center, but you should not delay repairs.

Why does P1123 appear after replacing the battery?

When the battery is disconnected ECU resets adaptive throttle settings. On some models Nissan (For example, Juke or Note) these settings are not restored automatically, and forced adaptation is required via a scanner or manual method (see spoiler above).

Could P1123 be caused by bad gasoline?

No, directly - no. However, low-quality fuel leads to:

• 🛢️ Contamination of the throttle and injectors (which indirectly causes P1123).
• 🔥 Detonation, which can damage control system sensors.

If the error appears after refueling, first check the valve for carbon deposits, and then change the gas station.

How to distinguish a TPS malfunction from a problem with the gas pedal?

In case of malfunction TPS:

• 📉 The speed fluctuates even without pressing the pedal.
• 🚗 Jerks occur at a constant speed.

If there is a problem with the pedal (APP):

• 🦶 There is no response to pressing the pedal or it is delayed.
• 🔍 Bugs P2122 or P2127 (pedal sensor low/high signal).

Is it necessary to flash the ECU with error P1123?

Only if:

• 🖥️ The error appeared after updating the firmware.
• 🔧 All other methods (cleaning, replacing the sensor) did not help.
• 📊 The scanner logs show unstable throttle adaptation parameters.

In all other cases, firmware is a last resort, as it can introduce new errors.