Code classification
What this reference means
The control module recorded a condition matching Catalyst System Efficiency Below Threshold (Bank 1). This identifies the monitored condition, not a guaranteed failed part. Software version, operating conditions and related codes must be considered together.
Monitored system: Catalyst efficiency monitoring — Bank 1
Possible symptoms
- Malfunction indicator lamp
- Often no immediate driveability symptom
- Readiness monitor may remain incomplete or fail
Possible causes to investigate
- Catalyst deterioration or contamination
- Exhaust leak affecting oxygen-sensor readings
- Upstream combustion, fueling or misfire fault
- Slow, biased or incorrectly installed oxygen sensor
- Incorrect sensor wiring or heater operation
- Non-original exhaust hardware or software mismatch
A list of possible causes is not a parts-replacement instruction. Test the circuit and system under the code's enabling conditions.
Workshop diagnostic sequence
- 01
Preserve freeze-frame, fuel trims, misfire counters and related oxygen-sensor codes.
- 02
Inspect exhaust leaks before and around the catalyst and sensors.
- 03
Correct misfire, oil consumption, rich/lean or fuel-control faults first.
- 04
Evaluate upstream and downstream sensor response under the OEM test conditions.
- 05
Check sensor heater circuits, wiring and part suitability.
- 06
Judge catalyst performance only after upstream causes are excluded.
Related technical context
Compliance
Safety and emissions-related faults must never be hidden on a road vehicle. Diagnose and repair the root cause. Required OBD and emissions systems must remain operational where the applicable law requires them.