Applicable Systems
OBD-II
Symptoms
The downstream oxygen sensor for bank 2 signal is below expected.
Possible Causes
- O2 sensor bank 2 sensor 2 failed low
- Wiring shorted to ground
- Connector corroded
- Catalyst bank 2 poor
- ECM sensor input fault
Troubleshooting Steps
- Step 1: Connect an OBD-II scan tool and read all stored DTCs and freeze frame data
All DTCs and freeze frame data are retrieved - Step 2: Inspect the related sensor or actuator wiring for damage, corrosion, or loose connections
Wiring and connectors are in good condition - Step 3: Use a digital multimeter to check sensor voltage, resistance, and reference signals per manufacturer specifications
Values are within specified range - Step 4: Perform component-level testing of the suspected sensor or actuator
Component passes or fails definitively - Step 5: Clear codes and road test to verify repair
Code does not return and system operates normally
How to Reset
To reset code P1421: 1) Repair the underlying fault. 2) Use an OBD-II scan tool to clear the DTC. 3) Perform a drive cycle.
Frequently Asked Questions
- Q: What does OBD-II code P1421 mean?
Code P1421 indicates: Oxygen Sensor Bank 2 Sensor 2 Circuit Low. This is a Toyota manufacturer-specific diagnostic trouble code.
- Q: Is code P1421 serious?
Severity: Major. Service as needed.
- Q: How do I fix code P1421?
Diagnose the O2 Sensor system and replace faulty components.
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Source: OBD-II Manufacturer Extended Codes / SAE J2012 / OBD-Codes.com
Category: OBD-II
Published: 2026-09-24
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