Lawmaking Fault Location Likely Crusade
P0420 Catalytic converter organization, bank 1 -efficiency below threshold
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What Does Code P0420 Mean?

OBD Ii error code P0420 is a generic code that is defined as ""Catalytic Converter System Bank 1, Efficiency below Threshold", and is gear up when the PCM (Powertrain Command Module) detects that the catalytic converter on Bank one is operating below a minimum allowable efficiency threshold. Note that "Bank 1" refers to the exhaust organisation on the banking company of cylinders that contains cylinder #1. Note also that the same definition applies to Nissan applications with a single bank of cylinders- on these applications, "Banking concern 1" can be disregarded.

The purpose of a catalytic converter is to catechumen harmful exhaust emissions (mainly oxides of nitrogen) into innocuous substances such every bit water and carbon dioxide. While pattern specifics vary between manufacturers, all catalytic converters consist of a substrate that is coated with catalysts in the form of inert metals such equally platinum, iridium, palladium, and others. Provided that the catalytic converter is at its optimal operating temperature, which also varies between manufacturers depending on the substrate and metals used, the catalysts convert harmful substances into less harmful ones as the exhaust stream passes over the catalysts.

NOTE: Note that the metals used in catalytic converters are called "catalysts" because they cause and sustain the conversion process, but are non themselves consumed in the conversion process.

However, even though almost OEM catalytic converters are designed to accept very long service lives, there are many factors at work (come across Causes section) in all applications that tin seriously touch on the efficiency of whatsoever catalytic converter. Therefore, the PCM uses a very simple, just relatively effective strategy to monitor the efficiency of all catalytic converters on the awarding on a continuous ground.

In practice, the PCM uses input data from two primary sensors- the #1 (upstream of the catalytic converter) oxygen sensor, and the #ii (downstream of the catalytic converter) oxygen sensor to calculate an efficiency value for the catalytic converter. Equally a practical matter, the upstream sensor monitors the composition of the exhaust gas, and the PCM makes adjustments to the fuel trims and ignition timing in direct response to input information received from this sensor, while the downstream oxygen sensor monitors the efficiency of the catalytic converter.

If the catalytic converter is in good condition and functioning properly, the bespeak from the downstream sensor will be most constant, equally opposed to the rapidly changing signal voltage from the upstream sensor. Thus, when the PCM compares the input data from the two oxygen sensors, it expects to see a difference between the ii point voltages, with the signal voltage from the upstream sensor fluctuating sharply, while the bespeak voltage from the downstream sensor should be adequately constant.

If however, the PCM detects a similar response from both sensors, it uses the degree of similarity to calculate an efficiency value for the catalytic converter based on how similar the two indicate voltages are. In most cases, the PCM volition gear up code P0420 and illuminate alarm calorie-free when information technology calculates an efficiency value of between 75%, and 70%, with 70% representing the everyman allowable efficiency threshold on near applications.

So why does code P0420 affect some Nissan applications more than others?

While code P0420 tin can afflict any application, this lawmaking is extremely common on Nissan applications such as Sentra, Rogue, Altima, and other models that are fitted with the QR25DE range of engines, which is widely regarded in the global auto repair industry as ane of the worst engines Nissan has ever produced.

While this engine has many other faults, its extremely high oil consumption rate is the primary reason why catalytic converters and air/fuel ratio sensors get clogged upwardly with oil, which is the primary cistron that affects the efficiency of these components, which in turn, causes lawmaking P0420 to set.

In short, the QR25DE engines' loftier rate of oil consumption stems from the fact that this engine is a modified version of the older, ii.0L QR20DE engine. By shortening the connecting rods of this engine, its deportation was increased to 2.5L, and while this increased power and torque considerably, the modification had the practical effect of increasing oil consumption because the pistons and piston rings were non reinforced to cope with the increased compression and combustion pressures.

Although Nissan introduced reinforced connecting rods, new pistons and revised piston rings for the QR25DE engine during 2007, the aluminum engine cake (as used on the QR20DE engine) was not reinforced, with the result that the loftier oil consumption charge per unit of the QR25DE engine was but partially corrected.

Other issues with the QR25DE include the facts that the retaining screws belongings the throttle flap in position work themselves loose and end upward beingness sucked into the engine, and frequent failures of the pre-catalytic converter. While in that location are no remedies for the mechanical deficiencies of the QR25DE engine, Nissan has released updated software that changes the fuel commitment characteristics of the fuel management system, which seems to accept reduced the high rate of catalytic converter failure on the QR25DE engine range somewhat.

Where is the P0420 sensor located?

The image to a higher place shows the location of the catalytic converter (circled) relative to the exhaust manifold on a Nissan Altima fitted with a QR25DE engine. Annotation that the manifold and catalytic converter form an associates, which means that the catalytic converter cannot be replaced separately.

What are the mutual causes of code P0420?

Bear in heed that if reprogramming the PCM does non resolve code P0420 on an application that has a QR25DE engine, there are many other possible causes to consider, some of which could include the following-

  • Unresolved excessive oil consumption (Near common)
  • Excessive fuel pressure, only note that this will almost certainly be indicated by a dedicated trouble code
  • Persistent misfire on one or more cylinders. Note that while misfires on whatsoever application can cause catalytic converters to fail, a misfire coupled with a high oil consumption rate will by and large crusade the converter to fail much sooner than on a misfiring engine with  normal oil consumption charge per unit.
  • Defective engine coolant sensor
  • One or more than lacking(leaking) fuel injectors
  • Loss of sensitivity of the affected air/fuel ratio sensor due to long use
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
  • Defective or contaminated air/fuel ratio sensor. Typical contaminants include engine oil, carbon, engine coolant, and silicon-based compounds constitute in some aftermarket gasket sealers, and some aftermarket fuel and oil additives
  • Lacking catalytic converter
  • Utilize of incorrect ,unsuitable, or contaminated fuel
  • Failed or failing PCM or other control module, but note that this is a rare issue, and the error must therefore be sought elsewhere earlier whatsoever command module is replaced.

Notation: While premature failure of catalytic converters due to excessive oil consumption on many Nissan applications is a mutual occurrence, there are many other possible causes of code P0420 on these applications. Therefore, it is important to tape all codes, likewise as all available freeze frame data nowadays, and to resolve all additional codes present in the order in which they were stored before condemning the catalytic converter out of hand.