Rick's Free Auto Repair Advice

Nissan P1421

Diagnose and fix Nissan P1421

Nissan has issued a service bulletin # NTB09-116a to address a Nissan P1421 COLD START CONTROL trouble code on all 2007 – 2010 Versa models with the MR18DE engine ONLY. The check engine light will appear and this Nissan P1421 trouble code will be stored. You won’t notice any drivability issues.

Nissan service bulletin # NTB09-116a

The bulletin advises owners to update the ECM software with a newer version. However, before you do that, shops find that cleaning the throttle body usually solves the problem.

See this post for instructions on how to clean an electronic throttle body.

After you clean the throttle body, you must perform a throttle body relearn procedure to teach the ECM the new “home” position. Perform the relearn in this order:

  1. Throttle Valve Closed Position Relearn Procedure
  2. Idle Air Volume Relearn Procedure

Nissan Throttle Valve Closed Position Relearn Procedure

Perform this procedure to teach the ECM the fully closed position of the throttle plate  It must be performed any time you disconnect the connector from the throttle body.

Make sure that the accelerator pedal is fully released.
Turn the ignition switch ON.
Turn the ignition switch OFF and wait at least 10 seconds.
Make sure that the throttle valve moves during the above 10 seconds by confirming the operating sound.
Done. Next, perform an Idle Air Volume Relearn Procedure

Nissan Idle Air Volume Relearn Procedure

The Idle Air Volume Relearn Procedure teaches the ECM the volume of air entering the intake manifold based on the position of the throttle plate. It must be performed any time the electric throttle body is cleaned or replaced.

Before performing the Idle Air Volume Learning, make sure that all of the following conditions are satisfied.

Battery voltage must be more than 12.9 V with the engine running
Engine coolant temperature must be 158 – 203°F
Transmission in Park/neutral position (PNP) switch ON (M/T): Selector in P or N for  A/T and CVT
Electrical loads OFF. AC, headlights (set parking brake before starting the engine; that will disable daytime running lights), rear window defogger, heated seats all OFF
The steering wheel pointed straight ahead
Transmission warmed up and driven for at least 10-mins
Turn off the engine and wait for at least 10-seconds
Without touching the accelerator pedal, turn the IGN switch to ON for at least 3 seconds but DO NOT START ENGINE.
Perform the following 5 times WITHIN 5-seconds
Fully depress and release then fully release the accelerator pedal
Wait for 7-seconds, then fully depress the accelerator pedal and hold it there for approximately 20-seconds until the check engine light stops flashing and stays lit.
Then fully release the accelerator pedal within 3-seconds after the check engine light lights solid.
Start the engine and let it idle.

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