P2189 Honda Prelude:  Lean Condition at Idle (Bank 2)

P2189 is a DTC code that can occur in your Honda Prelude.  It indicates the air fuel mixture is too lean at idle, specifically in bank 2 (we’ll cover how to find bank 2 later).  Its is different from the much more common P0174, which indicates that bank 2 is lean at any engine speed.

P2189 Honda Prelude

The technical definition for P2189 “System too lean at Idle: Bank 2”.  The code is thrown after the oxygen sensor on Bank 2 (usually sensor 1) has detected that the air fuel mixture is too lean.  It can be caused by a bad oxygen sensor, or a whole slew of problems.

The ideal air/fuel mixture is 14.7 parts air to 1 part fuel (14.7:1) When the air fuel mixture is too lean, it means that your car or truck has too much air for the amount of fuel present.  This can cause your vehicle to idle poorly, depending on how far from 14.7:1 the air fuel mixture is.

 

Bank 2 Location:  Honda Prelude

P2189 Bank 2

Bank one is the part of the engine with the second cylinder.  You’ll need to know to properly identify it in order to diagnose P2189.

On inline engines, it’s not relevant to know, as there is only one bank to deal with.  But, on V6 and V8 engines, there are two cylinder heads, and therefore two banks.  If you have P2189, you do need to determine which side of the engine has bank 2, unless you have P2187 as well, which is the code for a lean condition at idle for the first cylinder.  

If you have both codes, both sides of your engine are running lean at idle, and you don’t need to concern yourself with identifying which one is which.

Here’s how to tell where bank 2 is.

 

Symptoms

P2189 Check Engine Prelude

Here are some of the most common symptoms associated with P2189.  They are going to vary in severity depending on how far off the air fuel mixture is.

  • Rough Idle
  • Hard/No Start
  • Misfiring
  • Hissing/Whistling coming from the engine bay (this indicates a vacuum leak is the cause)
  • Smell of Gas

 

P2189 Causes:  Honda Prelude

Here are a few of the things that can make your Prelude’s engine run too lean at idle and cause P2189 in bank 2.  Most of them are easy enough to check, but there are a lot of them.  Here are some of the most common ones:

  • Vacuum Leak
  • Exhaust Leak
  • Fuel Injection Leak
  • Fuel Pressure Regulator
  • Fuel Pressure Low (clogged filter or bad pump)
  • Bad MAF sensor
  • Bad Gas Cap
  • EVAP Purge Valve

 

P2189 Diagnosis:  Honda Prelude

Here are some steps that you can use to diagnose P2189 in your Prelude at home.

Hopefully, there were other codes that were thrown with P2189.  If there are, it is a good thing, because it can make diagnosing it a whole lot easier.  For instance, if it’s an oxygen sensor related code, start with the oxygen sensors.  If it’s an EVAP code, start with the EVAP system.

If there aren’t any at all we can lower some of the causes listed above in the odds of causing the code column.  We want to focus on things that would cause ONLY ONE BANK to be lean.

It would mean that a bad fuel injector or oxygen sensor are highly likely.  An exhaust leak or vacuum leak where the intake manifold hits the cylinder head on the bank 2 side could also be a likely cause.

 

Super Easy Stuff

P2189 Troubleshootings

  • Gas Cap– Check to see if it is snugged down all of the way.  If you’ve gotten the check fuel cap warning a few times before this code was thrown, that indicates that a new fuel cap might fix the problem, or there is an EVAP leak.
  • Oil Cap– P2189 has been known to occur when there is no oil cap present, or if it is loose.  Take a second to check it real quick.
  • Smell for Gas– If you smell gas around the fuel injectors, that means that a fuel injector could be leaking.  It could also indicate that your Prelude has an EVAP issue.
  • Listen for a Hiss– A hissing or whistle sound coming from the engine indicates a vacuum leak.

 

Look for Leaks

A vacuum leak allows more air to enter your Prelude’s combustion chamber than the PCM is calling for, this air is unmetered, which would mean more air in the combustion chamber than the PCM thinks is going in there.  The O2 sensors pick up the air fuel mixture at idle and P2189 is triggered.

  • Check all of the hoses coming to and from the intake manifold for rot, damage, and loose connections.
  • Make sure the MAF sensor (if applicable) does not have leaks around it.
  • Look at the PCV valve and hose to see if they are leaking.

You can use carb cleaner to spray around these places.  If the engine RPM increases, you’ve found the vacuum leak and the likely cause of P2189.

 

Fuel System

If there isn’t enough fuel pressure, there won’t be enough fuel in the air fuel mixture, and it’ll run lean.  There are several components that can cause a fuel pressure to drop.

  • Bad Fuel Filter
  • Bad Fuel Pump
  • Clogged/Leaking Injector (very likely on a V6 or V8 where P2189 “Bank 1” is thrown but P2189 “Bank 2” is not thrown)

A bad fuel pump or fuel filter will produce lower fuel pressure.  But you’d likely get P2187 with it.

Here’s how to test fuel pressure.

 

Sensors

P2189 Diagnosis

If there doesn’t seem to be anything wrong with the vehicle physically, it’s likely one of your Prelude’s sensors that are at fault.

  • A bad oxygen sensor would give a false air/fuel reading and trigger P2189.
  • A bad MAF or MAP sensor will not properly read the air entering the engine, which could cause it to go too lean or rich.  In this case though, it’s too lean.

 

Conclusion:  Honda Prelude P2189

As you can see, there are many issues that can cause P2189 in the Honda Prelude.  How you go about attacking them is going to really depend on whether or not there were any other codes present, particularly P2187 or an oxygen sensor related code.

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