Skip the auto shop - Our mechanics make house calls

Q: Check Engine Light on - P2187 and P0420 codes

asked by on

About 4 months ago I installed a catless downpipe on my car. I did not get a tune because I was told that I don't need it if I don't want it. My car idles fine but starting it is weird. I've had times where I start the car and it shuts down. I hooked up a code reader to my car and I got the codes p2187(system too lean at Bank 1). Then a evaporative emission system leak(P0442). Also catalyst system efficiency below threshold bank 1(P0420).

My car has 61000 miles.
My car has a manual transmission.

Hello. If I understand correctly, when you say "catless downpipe," you mean that you have installed a pipe without a catalytic converter. If that is the case, you are always going to have the code for catalyst efficiency.

The car has two oxygen sensors, one upstream and one downstream of the catalyst. The controller is looking for a specific oxygen level going in and coming out of the catalyst to indicate that it is doing its job. Without the catalyst, the controller will never see the levels it’s looking for and will always light the CEL.

This won’t effect the way the car runs, but in most states it means you won’t be able to pass inspection. Additionally, if the CEL is always on, it won’t be able to alert you to any new problems. As for the system too lean and EVAP codes, they may have the same cause. It’s possible that you dislodged or damaged a vacuum line while you were doing the work. The resulting vacuum leak could cause the P2187 and if the leak is on the evaporative vent line it could cause the P0442. Look for a damaged or disconnected vacuum hose. If you don’t find one, you may want to enlist the help of a certified technician to diagnose the Check Engine Light and guide you with any repairs needed.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Check Engine Light on - P2187 and P0420 codes

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: No codes, vibration at idle

I might recommend using a bottle of fuel injector cleaner in the gas tank and some Seafoam in the oil. Those together will normally smooth out any rough idle that can be fixed with cleaners.

Q: My car shows trouble codes P0133 and P0420

Hi there: It appears as if you've got a lot of miscommunication going on with your mechanic. Here are a few basics. First, anytime an error code is triggered, such as the P0133 OBD-II code the issue needs to be...

Q: My left turn signal started clicking very fast recently and now when I start the SUV it will run then shut off while in drive.

Hi there. For your situation, check all of the ground wires on the battery, alternator, and fuse boxes. Make sure that the mounting bolts are tight and that the ground wires are clean. Check the battery cables for looseness and...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...