P2423

Code

Generic P — Powertrain

HC Adsorption Catalyst Efficiency Below Threshold Bank 1

Brand: Generic

Type: P — Powertrain

Views: UK: 23 EN: 59 RU: 26

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty or degraded HC adsorption catalyst (Bank 1)
Contaminated or clogged adsorption substrate (oil, coolant, fuel additives)
Exhaust leak upstream of the adsorption catalyst
Rich-running condition or persistent misfires increasing HC load
Faulty downstream sensor(s) or heater (O2/UEGO/catalyst monitor)
Wiring, connector corrosion, or poor signal to PCM

Symptoms

Check Engine Light (MIL) illuminated
Elevated tailpipe hydrocarbon readings or failed emissions test
Poor fuel economy (if rich-running condition present)
Occasional rough idle or drivability issues if misfires present
No significant symptom other than MIL until severe degradation

What to check

Read and record freeze frame and freeze data for the code
Check OBD monitor status and pending codes; verify code is current
Visual inspection of exhaust components, sensors, and wiring on Bank 1
Check for exhaust leaks upstream of the adsorption catalyst
Scan live data: upstream and downstream O2/UEGO signals, fuel trims, misfire counters
Verify heater operation/power to O2 sensors (if applicable)

Signal parameters

Upstream oxygen sensor voltage/response (Bank 1 Sensor 1)
Downstream oxygen sensor voltage/response (Bank 1 Sensor 2 or catalyst monitor)
O2 sensor heater current/voltage (where applicable)
Short-term and long-term fuel trim values
Misfire counts or misfire detection counters
Fuel rail/pressure (direct injection vehicles)

Diagnostic algorithm

Verify the code: connect a scan tool, record freeze frame, note driving conditions when code set.
Clear codes and perform drive cycle to attempt to reproduce; confirm code returns to eliminate one-time events.
Perform a visual inspection of Bank 1 exhaust, adsorber/catalyst, sensors and wiring/connectors for damage or contamination.
Check for exhaust leaks upstream of the adsorption catalyst (smoke test or visual); repair leaks if found and re-test.
Monitor live data: compare upstream vs downstream O2/UEGO responses during rich/lean transitions and steady load. Downstream should be more stable if catalyst working.
Evaluate fuel trims and misfire history. Diagnose and repair any ongoing misfires or fuel control issues (injectors, fuel pressure, ignition) that can overload the catalyst.
Test O2/catalyst monitor sensors: verify heater circuit operation, sensor response times and voltages; repair or replace faulty sensors or harness as needed.
If sensors and engine operation are good, check for contamination of the adsorption substrate (oil/coolant/fuel) — inspect upstream components for causes of contamination.
Measure tailpipe HC (ppm) upstream and downstream if equipment available to quantify catalyst/adsorber efficiency.
If evidence confirms degraded adsorption catalyst (high downstream HC with correct sensors and no engine faults), replace adsorption catalyst/substrate assembly and clear codes.
After repairs, perform a full drive cycle and re-scan to confirm the code does not return. Follow any manufacturer reprogramming or post-replacement procedures if required.

Likely causes

Adsorption catalyst worn or saturated with contaminants
Upstream misfire or fuel trim problem causing high HC emissions
Faulty downstream oxygen sensor (Bank 1 downstream) reporting incorrect efficiency
Exhaust leak between engine and adsorption catalyst
Wiring harness corrosion or connector fault at downstream sensor

Fault status

⚠️ Status

HC Adsorption Catalyst Efficiency Below Threshold (Bank 1) — check downstream sensor, exhaust integrity, engine running condition, and adsorption catalyst condition.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours