P2423 Code Definition A P2423 code is a generic powertrain code related to emissions systems problems. In this case, the hydrocarbon adsorption and catalyst efficiency is below the allowed threshold in engine bank 1 (typically the number 1 cylinder). This code is related to: P2424: HC Adsorption Catalyst Efficiency Below Threshold Bank 2 What the P2423 Code Means The Hydrocarbon Absorptive Catalyst (HCAC) system includes a three-way catalyst and two heated oxygen sensors. The three-way catalyst absorbs hydrocarbons emitted soon after the engine is started. If a P2423 code appears, engine bank 1 is signaling that its hydrocarbon adsorption and catalyst efficiency is below the allowed threshold. The engine control module (ECM) takes exhaust composition and temperature information from the vehicle’s oxygen sensors and determines the degree of needed catalyst efficiency. If the level detected varies from the necessary amount, a P2423 code will be stored. What Causes the P2423 Code? A P2423 code is caused by a number of possible problems, including: Damaged or defective catalytic converter Damaged or defective oxygen sensors (will typically accompany an oxygen sensor diagnostic trouble code) Incorrect fuel use Damaged or defective coolant temperature sensor Damaged or defective mass air flow sensor Damaged or defective manifold air sensor Damaged or defective fuel pressure regulator or fuel injection system/components Ignition misfire Oil contamination Possible leaks from exhaust components upstream from the catalytic converter What are the Symptoms of the P2423 Code? Warning or Check Engine Light may illuminate Vehicle may go into “limp” mode Vehicle may hesitate during acceleration Vehicle may sound different when accelerating, making “hissing” noises Engine may stall Engine may not start How Does a Mechanic Diagnose the P2423 Code? A mechanic may use one or more of the following methods to diagnose a P2423 code: Use an OBD-II scanner to check for a stored P2423 code Inspect the exhaust system for leaks Visually inspect all wiring and connectors for damage Use a temperature gun to measure exhaust pipe temperatures before and after the catalytic converter Measure upstream and downstream oxygen sensor operations on bank 1 with an oscilloscope Upstream measurements should be between 0.350 and 0.900 volts in closed-loop operation Downstream measurements should be around 0.500 volts and hold during the duration of the engine idle Common Mistakes when Diagnosing the P2423 Code When failures revolving around the catalytic converter occur, one of the most common mistakes include not completely understanding the initial cause of the failure. Engine misfires or rich exhaust levels can cause catalytic converter failure due to deterioration of the platinum. Failing to fix the causes of these issues first can result in unneeded repairs. Oxygen sensor failure should also be checked. How Serious is the P2423 Code? Because a vehicle can stall and possibly go into “limp mode, and operation can become dangerous, YourMechanic considers this a serious code and recommends getting this diagnosed and repaired as soon as possible to protect the car from further damage. What Repairs can Fix the P2423 Code? Repairs that can fix a P2423 code can include: Repairing any leaks in the exhaust system Repairing or replacing any frayed or shorted wires or damaged connectors Repairing or replacing any damaged oxygen sensors (Note: an oxygen sensor code should also be stored on the ECM if doing this repair) Replacing a damaged or defective catalytic converter Clearing the codes, test driving the vehicle, and rescanning to see if the codes reappear Additional Comments for Consideration Regarding the P2423 Code A catalytic converter failure is typically a sign of additional, serious problems. Problems upstream from the catalytic converter may be read by the ECM as a failure of the catalytic converter, resulting in speedy, unnecessary repairs or replacement of the catalytic converter. Always resolve any oxygen sensor codes before working to fix a catalytic converter code. In addition, catalytic converters are typically backed by a 100,000-mile federally mandated warranty, so check to see if it is still covered before making repairs. Need Help with a P2423 Code?