Trouble CodeFault LocationProbable Cause
P0421 Warm up catalytic converter, bank 1 -efficiency listed below threshold Catalytic converter, wiring, HO2S 2

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What Does code P0421 Mean?

If friend are analysis this, i assume that your OBD-II equipped car has save a code P0421. This method that the powertrain control module (PCM) has actually detected a difficulty with the effectiveness of the catalytic converter heat up function for engine financial institution one. Financial institution 1 suggests that the breakdown has arisen in the financial institution of the engine that includes the number one cylinder.

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The catalytic converter is supplied to mitigate exhaust emissions native diesel and gasoline sustained engines. It is created using a filtration element of ceramic and also precious steels enclosed in a steel housing and placed in the exhaust pipe. Harmful nitrogen oxides (N2O), carbon monoxide, and unburned hydrocarbons room all convert to harmless ion of nitrogen, oxygen, carbon dioxide, and water inside the catalytic converter. This is achieved using the thick web of filtration and also the excessive heat of the engine exhaust. Catalytic converter temperatures have to reach at least 800-degrees Fahrenheit.

Catalytic converter performance is monitored using upstream and downstream oxygen (O2) sensors. The O2 sensors space zirconium dioxide sensing elements enclosed in vented stole housings, linked to cable leads in the O2 sensor wiring harnesses through platinum electrodes. O2 sensor wiring harnesses are linked to the PCM via the controller area network. The O2 sensors administer the PCM v data regarding the percentage of oxygen corpuscle in the engine exhaust as contrasted to the oxygen contents of the approximately air.

Spent engine exhaust gases are pushed through the exhaust manifold, into the exhaust pipe, end the upstream O2 sensor, with the catalytic converter, and they happen over the downstream O2 sensor. Exhaust gases circulation through vent holes in the steel housing and across the sensing facet of the O2 sensors as outside air is attracted into a chamber in the middle of the sensors v the cable lead cavities.


Inside the chambers, the air is heated, forcing the oxygen ions to develop (energy) voltage. Deviations in between the concentration the oxygen molecule in ambient waiting (drawn into the O2 sensor) and also the concentration of oxygen ion in the exhaust cause voltage fluctuations. These deviations cause the oxygen ions inside the O2 sensor come bounce from one platinum layer come the other, really rapidly and repetitiously. Fluctuations in voltage take place as the surging oxygen ion bounce in between platinum layers. The PCM identifies these changes in voltage as variations in exhaust oxygen concentration. This variations signify whether the engine is to run lean (too small fuel) or well-off (too much fuel). Once the signal calculation from the O2 sensor is lower, more oxygen is present in the exhaust (lean condition). If the voltage signal calculation is higher, much less oxygen is current in the exhaust (rich condition). This data is provided by the PCM come compute fuel shipment strategy and ignition timing, and also other things.

If the upstream and downstream O2 sensors reflect a comparable exhaust oxygen concentration, a code P0421 will be stored and also a break down indicator lamp might be illuminated.

What space the common reasons of password P0421 ?

Faulty catalytic converterA faulty mass air circulation or manifold air push sensorDefective O2 sensor/sBurnt, chafed, broken, or disconnected wiring and/or connectorsEngine exhaust leak

What space the symptom of password P0421 ?

Diminished fuel efficiencyA lack of general engine performanceOther related diagnostic trouble codes may also be storedService engine soon lamp illumination

How do you troubleshoot code P0421 ?

A diagnostic scanner, digital volt ohmmeter (DVOM), and a reliable auto information resource (such together All Data DIY) will prove vital when diagnosing a password P0421.

Misfire codes, throttle position sensor codes, manifold air push codes, and mass air flow sensor codes need to be addressed prior to attempting come diagnose a stored code P0421. The engine must be to run efficiently prior to diagnosing this code.

With a P0421, ns would start with a visual inspection of device wiring harnesses and also connectors. Meticulously inspect harnesses that room routed near warm exhaust pipes and manifolds, and also those that room routed near sharp edges like the ones uncovered on exhaust shields.

Proceed through connecting the scanner to the car diagnostic port and also retrieving all trouble codes and freeze structure data. Create this information down due to the fact that it might be beneficial if this proves to be an intermittent code. Intermittent codes have the right to be much harder to diagnose. Now, clear the codes and also test journey the vehicle.

If the P0421 is automatically reset, begin the engine and allow it come reach normal operating temperature, then permit it come idle (with the transmission in neutral or park). Use the scanner data stream to observe O2 sensor entry data. Narrowing the data present to include only pertinent data will yield much faster data response. If the engine is running efficiently, the upstream O2 sensor will certainly cycle on regular basis from one-millivolt (.100-volts) to nine-millivolts (.900-volts) and downstream O2 sensor data have to reach a mid-line and settle there. If upstream and downstream O2 sensor readings are too similar, ~ the PCM has actually reached closeup of the door loop operation, suspect a defective catalytic converter.

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Use the DVOM to examine resistance that the O2 sensor/s in question, as well as voltage and ground signals for O2 sensor circuits. Usage caution and also disconnect associated controllers before attempting come test system circuit resistance through the DVOM.