P2423 — HC Adsorption Catalyst Efficiency Below Threshold Bank 1

P2423 — HC Adsorption Catalyst Efficiency Below Threshold Bank 1. A fault in the catalytic converter efficiency monitoring. The car is usually drivable while you plan the repair. Typical causes: aged or contaminated catalytic converter, engine misfires damaging the catalyst, persistent rich or lean fuel mixture.

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK Usually safe to drive for a limited time: the car remains drivable, but emissions are elevated and fuel economy suffers. Do not postpone if you notice power loss, overheating of the exhaust, or a strong smell — a clogged converter can damage the engine.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm P2423 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the catalytic converter efficiency monitoring for damage, corrosion, chafing or poor contact.
  4. Subsystem check Compare upstream and downstream O2 sensor waveforms in live data — a healthy converter smooths the rear signal.
  5. Subsystem check Check for exhaust leaks and rule out misfire codes before condemning the converter.
  6. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2423 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P2423 (parts and labor, USD, independent shop rates): Replace the catalytic converter: $800–$2,500; Repair an exhaust leak: $100–$350; Replace an oxygen sensor: $150–$450. Overall, fixing P2423 usually costs between $100 and $2,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of P2423?

The most common causes are: aged or contaminated catalytic converter, engine misfires damaging the catalyst, persistent rich or lean fuel mixture.

Is it safe to drive with P2423?

Usually safe to drive for a limited time: the car remains drivable, but emissions are elevated and fuel economy suffers. Do not postpone if you notice power loss, overheating of the exhaust, or a strong smell — a clogged converter can damage the engine.

How do I diagnose P2423 myself?

Start with a scan: confirm P2423, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the catalytic converter efficiency monitoring, and verify the suspect component against live data before buying parts.

How much does it cost to fix P2423?

Replace the catalytic converter — $800–$2,500; Repair an exhaust leak — $100–$350; Replace an oxygen sensor — $150–$450. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What does OBD2 code P2423 mean?

P2423 — HC Adsorption Catalyst Efficiency Below Threshold Bank 1. A fault in the catalytic converter efficiency monitoring. The car is usually drivable while you plan the repair. Typical causes: aged or contaminated catalytic converter, engine misfires damaging the catalyst, persistent rich or lean fuel mixture.

What does P2423 mean?

Seeing P2423 on your scanner? The control unit has caught the catalytic converter efficiency monitoring operating outside its calibrated window. The formal description is “HC Adsorption Catalyst Efficiency Below Threshold Bank 1”, and the code is grouped under powertrain (engine/transmission) faults.

“Bank 1” means the side of the engine that contains cylinder 1. Verify which side that is on your specific engine before testing or replacing parts.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores P2423 and switches on the warning light. Freeze frame data saved with the code shows the exact conditions — rpm, load, temperature, speed — at the moment the fault was detected, which is the best starting point for diagnosis.

What causes P2423?

  • exhaust leak ahead of the converter
  • aged or contaminated catalytic converter
  • engine misfires damaging the catalyst
  • faulty downstream or upstream oxygen sensor
  • oil or coolant entering the exhaust

Common symptoms of P2423

  • rattling noise from under the car
  • slight loss of power at high rpm
  • sulfur or rotten-egg smell from the exhaust
  • failed emissions test
  • increased fuel consumption

How to diagnose P2423

  1. Connect an OBD2 scanner, confirm P2423 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the catalytic converter efficiency monitoring for damage, corrosion, chafing or poor contact.
  4. Compare upstream and downstream O2 sensor waveforms in live data — a healthy converter smooths the rear signal.
  5. Check for exhaust leaks and rule out misfire codes before condemning the converter.
  6. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2423 does not return.

How to fix P2423

Start with the cheapest and most common causes before replacing expensive parts:

  • Replace the catalytic converter — $800–$2,500
  • Repair an exhaust leak — $100–$350
  • Replace an oxygen sensor — $150–$450

How much does it cost to fix P2423?

Repair cost depends on which component actually failed. Typical scenarios for P2423 (parts and labor, USD, independent shop rates):

  • Replace the catalytic converter: $800–$2,500
  • Repair an exhaust leak: $100–$350
  • Replace an oxygen sensor: $150–$450

Overall, fixing P2423 usually costs between $100 and $2,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P2423?

Usually safe to drive for a limited time: the car remains drivable, but emissions are elevated and fuel economy suffers. Do not postpone if you notice power loss, overheating of the exhaust, or a strong smell — a clogged converter can damage the engine.

Related OBD2 codes