2021-2022 Nissan Sentra MIL On for P0401 and P0404

Symptoms

Owners of 2021-2022 Nissan Sentra vehicles may observe the Malfunction Indicator Lamp (MIL) illuminated on the dashboard. This warning light is typically accompanied by the storage of Diagnostic Trouble Code (DTC) P0401, indicating "EGR A FLOW INSUFFICIENT," and/or DTC P0404, indicating "EGR A CONTROL," within the Engine Control Module (ECM).

It is important to note that this condition, while triggering the warning light and storing these specific codes, is not associated with any noticeable drivability concerns. The vehicle should otherwise operate normally.

Fault Codes / DTCs

When the Malfunction Indicator Lamp (MIL) illuminates, technicians may find the following diagnostic trouble codes stored in the ECM:

Code	Description
P0401	EGR A FLOW INSUFFICIENT
P0404	EGR A CONTROL

Diagnosis / Trigger Conditions

To confirm if your 2021-2022 Nissan Sentra is affected by this issue, a technician will verify that the MIL is illuminated and either DTC P0401 or P0404 (or both) are stored in the ECM. Crucially, there should be no other drivability concerns present.

The technician will then use the CONSULT-III diagnostic tool to confirm the current ECM part number. This part number must match one of the specific numbers listed in Nissan's technical documentation for the bulletin to apply. If the ECM part number does not match, this bulletin does not apply, and further diagnostics would be required.

Applicable ECM Part Numbers (23710- prefix):

Year	Current ECM Part Number
2020	6LB3B, 6LB3C, 6LB9B, 6LB9C, 6LC2B, 6LC2C, 6LC2D, 6LC3B, 6LC3C, 6LC3D
2021	6LJ6B, 6LJ6C, 6LJ7B, 6LJ7C, 6LJ8B, 6LJ8C, 6LJ9B, 6LJ9C, 6LW0A, 6LW0B, 6LW0C, 6LW1A, 6LW1B, 6LW1C, 6LW2A, 6LW2B, 6LW2C, 6LW3A, 6LW3B, 6LW3C, 6LW3D
2022	6LX0A, 6LX0B, 6LX0C, 6LX1A, 6LX1B, 6LX1C, 6LX2A, 6LX2B, 6LX2C, 6LX3A, 6LX3B, 6LX3C

Repair Procedure Summary

The primary solution for the Nissan Sentra P0401 P0404 issue involves reprogramming the Engine Control Module (ECM). This is a software update designed to correct the logic that triggers the MIL for these specific EGR-related codes.

Before the reprogramming, several preparatory steps are crucial to prevent damage to the control unit:

1. Connect Diagnostic Equipment: An AC adapter must be connected to the CONSULT PC, and the CONSULT PC must be connected to the internet via Wi-Fi or a network cable.
2. Software Updates: Ensure the ASIST software on the CONSULT PC is synchronized and all necessary software updates are installed.
3. Minimize Interference: All external Bluetooth® devices (e.g., cell phones, printers) within range of the CONSULT PC and the Vehicle Interface (VI) must be turned off to prevent interruption during reprogramming.
4. Vehicle Preparation: Turn off all vehicle electrical loads, but turn on the hazard warning lamps. A battery maintainer or smart charger, set to reflash mode, must be connected to ensure the battery voltage remains between 12.0 V and 15.5 V throughout the process.
5. Idle Air Volume Learning Conditions: The vehicle should be driven for approximately 10 minutes to meet specific conditions required for Idle Air Volume Learning, including an engine coolant temperature between 158-212°F, battery voltage above 12.9 V (at idle), and a warmed-up transmission.

Once these conditions are met, the ECM will be reprogrammed. After successful reprogramming, the technician must perform several post-reprogramming procedures: Throttle Valve Closed Position, Idle Air Volume Learning, Accelerator Closed Position, and DTC Erase. A printout showing the ECM part numbers before and after the update should be attached to the repair order.

Required Tools or Parts

To perform this repair, technicians will utilize the Nissan CONSULT-III diagnostic system. A battery maintainer or smart charger capable of maintaining voltage between 12.0 V and 15.5 V is also essential during the reprogramming process.

Important Warnings

Nissan emphasizes that these bulletins are intended for use by qualified technicians, not 'do-it-yourselfers'. Attempting this repair without proper training, equipment, and safety instructions could lead to further issues or damage. Owners should not assume a described condition applies to their vehicle without dealer verification.

Furthermore, it is critical to turn off all external Bluetooth® devices near the CONSULT PC and Vehicle Interface (VI) during the reprogramming process. Bluetooth® signal waves can interrupt the reprogramming, potentially damaging the control unit.

What Owners Should Know

If your 2021-2022 Nissan Sentra displays the Malfunction Indicator Lamp (MIL) and diagnostic checks reveal DTC P0401 or P0404, it is likely due to a software anomaly in the Engine Control Module (ECM). This issue does not typically affect the vehicle's performance or drivability.

The resolution involves a software update to the ECM, which must be performed by a qualified Nissan technician using specialized diagnostic equipment. This is not a recall, but a technical service bulletin providing guidance for dealers on how to address a known condition. Contact your authorized Nissan dealer to have your vehicle diagnosed and the ECM reprogrammed if applicable.

Source: NHTSA ID 10218654