Let’s face it, the b15 Sentra is now anywhere from 15 to 20 years old and there will be times where you decide to get under the hood to detail the bay, possibly remove your intake box to clean the throttle plate to gain that .001 HP 😂 or maybe you’ve had a MAF sensor go bad and it’s time to replace it, but forgot to plug it in before starting the car, OOPS! I’ve done this myself early on.
Upon starting the car after the work you performed, you notice the idle is off or the car doesn’t want to rev out the way it should. The reason for this, is the ECU goes into whats called safe mode (there are a few different names for this) where the ECU goes into a protective mode, so the engine isn’t damaged in any way due to something not being plugged in or perhaps a failed sensor. Yes, this is designed to do this, so don’t worry.
By performing the Idle Relearn, you are going to be manually resetting the system back to its normal operations, by performing a series of events with the ignition and throttle pedal. These particular events need to be done in a timed sequence otherwise the ECU won’t be able to “RELEARN“. Depending on your coordination this may take you a few try’s to get it right, but once you have completed this once, it’s a piece of cake after that.
In the video below, the Idle Relearn is described in a step by step process with a timer to ensure accuracy during the relearn. Before proceeding to the video, skip to the bottom half of this post to read about the certain conditions that need to be met for this to work. I hope this helps!
This is the Idle relearn video for the 2002 - 2006 Sentra and other NISSAN models: https://youtu.be/TZJfWQLGUZI?t=5
ENGINE CODES p0507 p2102 p0603 p2118 P0123 and P0233
Before performing Idle Air Volume Learning, make sure that all of the following conditions are satisfied. Learning will be cancelled if any of the following conditions are missed for even a moment.
Battery voltage: More than 12.9V (At idle)
Engine coolant temperature: 70 - 100 C (158 - 212 F)
Park/neutral position (PNP) switch: ON (Shifter in Park or Neutral)
Electric load switch: OFF (Air conditioner, headlamp, rear window defogger)
Steering wheel: Neutral (Straight-ahead position) Vehicle speed: Stopped