Explaining Trouble Codes PO420 - PO421- PO430 - PO431

WHAT IT MEANS WHEN YOUR GET A CODE READ OF PO420 OR PO430

It is important to remember that if your "Check Engine Light" illuminates and someone just simply reads a code of PO420, 421, 430 or 431 this does not necessarily mean the Catalytic Converter is bad!  All that code says is either Converter operating below efficency or Converter operating below threshold.  No where in the interpretation of that code does it say the converter is bad.  Your vehicle may very well need a Catalytic Converter but to determine this, your mechanic or technician should perform proper engine diagnostics.  Just reading a simple code is NOT considered diagnostics.  The following material should give you a better understanding of what proper diagnostics consist of and how they should be performed.  If after reading this material you still have questions please give us a call, 888-240-7088, and we will do all we can to help you solve the problem;

When your vehicle generates those emission codes it simply means that the converter is not able to function properly. Remember that the catalytic converter is at the very end of the emission diagnostic system, and a number of things can go wrong upstream of the converter that can cause. a PO420 (or PO430) MIL light illumination.

PO420 or PO430 CODE CATALYTIC CONVERTER FAILURE DIAGNOSTICS

Following is a list of procedures that should be accomplished before the final determination that a new catalytic converter is needed.  These are known as diagnostic procedures and go far beyond someone just performing a simple code reading and then declaring a bad converter is present.  That is not performing proper diagnostics and even after a converter replacement you might end up with the same problem! Cars today are not smart enough to tell us or a mechanic what is wrong with them...they do tell us what hurts and it is then up to the technician or mechanic to diagnose the root problem.  The following items will outline proper diagnostics in determining whether a converter is good or bad.

EXHAUST RELATED ERROR CODES

There are 711 possible PO generic DTC error codes. Only 7 of the 711 codes are exhaust related.

PO401:      Insufficient EGR Flow

PO402:      Exhaust Gas Recirculation (EGR) Excessive Flow Detected

PO410:      Secondary Air Injection System Malfunction

PO420:      Catalyst System Efficiency Below Threshold (Bank 1)

PO421:      Warm-Up Catalyst Efficiency Below Threshold (Bank 1)

PO430:      Catalyst System Efficiency Below Threshold (Bank 2)

PO431:      Warm-Up Catalyst Efficiency Below Threshold (Bank 2)

THINGS TO ASK YOURSELF OR YOUR CUSTOMER

Have there been any driveability or performance issues with the vehicle, have there been any recent repairs or tune-up work performed, if so was the check engine light reset and were the codes recorded on previous repair orders.

Do not rely on scan tool data alone. In most applications, the customer will have the check engine light reset prior to repair. If the original cause of converter failure is intermittent, only the catalyst failure code may show up (masking the original reason for converter failure).

VEHICLE TEST

• If possible, test-drive the vehicle and note any driveability issues that may indicate fuel or spark delivery problems such as hesitation, stumbling, spark knock or signs of misfire.

• Idle smoothness. Check for any signs of surging or roughness, indicating misfire or improper fuel delivery.

• Check the tailpipe, particularly immediately following start-up, for any smoke indicating too rich AFR (black smoke), water/antifreeze (white Smoke), or oil (blue smoke).

• Listen to engine carefully for any signs of vacuum or exhaust manifold leaks.

• Inspect intake system for signs of oil indicating excessive blow-by or cracks that may cause leaks.

• Inspect spark plugs/wires and air filter.

• Scan tool test.

• Do not reset MIL light!!

• Read the OBD-II readiness tests to ensure all tests have been completed. If the tests have not been completed, chances are the MIL was recently reset, possibly hiding intermittent problems.

• Read trouble codes (if any) and inspect as necessary.

• Read pending trouble codes (if any) and inspect as necessary.

• With engine running and at operating temperature, read scan data list. This is typically a tible listing all available sensors and outputs.

• Look at Long Term Fuel Trims (LTFT). These show the amount (in %) the computer is modifying fuel delivery, based on the ₀₂ sensor feedback. Positive numbers indicate the computer is adding fuel, negative numbers indicate the com­puter is removing fuel. Large positive numbers (>10%) should be investigated further as they indicate the computer is adding more fuel than originally designed.

• Look at the O2 sensor output signals.  Sensor 1 is before the converter, Sensor 2 is behind the converter, Bank 1 and 2 are typically used in V-configuration where Bank 1 is on the side Cylinder 1 is located.  Some inline 6 cylinder engines have Bank 1 as Cylinders 1-3 and Bank 2 as Cylinders 4-6.  The sensors are usually abbreviated as O2S1B1 (O2 Sensor, Bank 1)

• Sensor 1 output should be very active and oscillate rapidly from approximately 0 to less than 1 volt. If the signal tends to show high voltage with little fluctuation, excessive unburnt fuel is reaching the sensor. If Sensor 1 shows low or no voltage, the sensor could be defective, or there might be an exhaust leak in front of or immediately behind the sensor, or there could be a lack of fuel delivered to the combustion chamber. If the sensor does not respond to a rapid accelerator kickdown, chances are the sensor is defective. If it does respond, an exhaust leak or lack of fuel is indicated. (The preceding test must be done after the engine and exhaust system have been allowed to fully heat up.)

• Sensor 2 should show a fairly steady signal. It is not critical what the signal is, only that it does not oscillate as frequently as the front. If the signal is above 250mV, the sensor is fine. If it is below, check for activity by rapid accelerator kick-down or by raising the engine speed to approximately 2000 rpm. Any movement indicates the sensor is fine.

The material above is designed to give our customers a better insight to their need of a catalytic converter replacement.  If you have been told that a new converter is required on your vehicle from someone just reading a "check engine light" code then they are not performing true diagnostics on that vehicle.  Cars today are not smart enough to tell us what is wrong with them just by generating codes, they can simply tell us what hurts and then it's up to a technician or mechanic to interpret those codes and from there get to the root of the problem.

If you still have questions or would like us on to talk directly to your mechanic on your behalf, please give us a call at 888-240-7088 and we will be happy to assist you.

RETURN TO HOME PAGE