The Error code P0430 – efficiency below threshold bank is a DTC or a diagnostic trouble code. It is a check engine light code which indicates that the catalyst’s system efficiency is less than the required threshold. In simple terms, it means that more pollution is added into the air than what was supposed to be because of your car.  This problem can be caused by problems with the fuel system, 02 sensors that are damaged, a catalytic converter that is clogged or perhaps the combination of all three.

The P0430 code is quite the common trouble code. Information about error code P0430 is put together below in order to help you in identifying diagnostic steps that you can take in order to fix the problem.


In order for the car to be able to keep a reasonably low emission of carbon monoxide, hydrocarbons and oxides of nitrogen, a three-way catalytic converter is used by the engine control system. Within the converter is the catalyst which promotes a chemical reaction that oxidizes the CO and HC within the exhaust gas. It is through this chemical reaction that HC and CO are converted into carbon dioxide and water vapor that is basically harmless. Moreover, this reaction also effectively reduces the NOx and then converts it into Nitrogen.

This process is monitored using Bank 2, which is located inside of the exhaust stream at the three-way catalytic converter. This is what produces the signal output indicating the catalyst’s storage capacity. Basically, the P0430 code is a trouble code used to indicate that the sensor in the catalytic converter located in bank 2 has detected that the converter is not working properly. This trouble code indicates that the converter is not working as efficiently as it should have been according to its specs.

Common Symptoms

The common symptom that indicates this condition exists is when the PCM or Powertrain Control Module detected excessive Bank 2 activity than what was within its acceptable range over a period of time. Other symptoms that may indicate this problem are when the Check Engine Light illuminates and when there is a visible lack of engine power. In other times, however, no abnormal symptoms can be noticed.

Possible Causes

Error code P0430 may have happened because of one or more of these things:

  • Catalytic converter that is defective
  • Damage in the internal engine which results in the high consumption of oil
  • Leaking Head Gasket which has possibly damaged the Catalytic Converter
  • Exhaust tube, air leaks intake or leaks in the fuel injector
  • Faulty fuel injector
  • Improper ignition timing
  • Faulty sparks plug

How to Check

Catalytic converters fail because of normal degradation, physical damage, overheating, contamination, substrate restriction or due to internal disintegration. Physical damage is a common cause of a DTC P0430 but before the converter should be replaced, you have to first check specifically for the main cause of the problem. In order to check if it is truly not working effectively according to the specifications and as it should have really been, you can try these tests in order to see if the converter is functioning well.

  1. First, check whether the fire element of the converter has not been crushed to pieces. This can be done simply by banging it with your palm. You will hear pieces rattling inside if it really is crushed.
  2. Next would be by using a scan tool in order to verify whether the downstream oxygen sensor is rich.
  3. See if the downstream oxygen sensor works by inducing Rich condition by spraying small amount of carburetor cleaner in the vacuum hose and see if the O2 sensor in the rear reports it. This will also require a scan tool.
  4. See if the downstream oxygen sensor is working properly by inducing it to Lean Condition by means of removing large vacuum hose. When this is done, check to see of if the vacuum leak is reported by the downstream sensor.

On the other hand, when you are looking for internal disintegration, you can check by using a rubber mallet to lightly rap the converter. If it rattles, it would mean that the wrap that insulates the substrate against the catalyst converter has become lose or perhaps the substrate itself has disintegrated.

How to Fix

Here are some suggestions as to how you can fix a P0430 error code:

  • Inspect the exhaust for leaks.
  • Next, measure the oxygen down the sensor at Bank 2. Also, while you are at it, it would be best to test the oxygen O2 sensor.
  • If you have a newer car, it may have a warranty for this issue, as there are a lot of vehicle manufacturers that offer warranty when it comes to parts related to emissions.
  • You can use a cleaner to remove any carbon buildup that is causing the error code although it is not as fool-proof.
  • Giving your car a tune-up would be best idea when the steps provided above did not work.