P0427
Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 1
Emissions (catalyst)
Generic OBD-II
Medium
What it means
P0427 means the ECM sees a lower-than-expected voltage from the bank 1 catalyst temperature sensor. That sensor lets the computer monitor how hot the catalytic converter runs; a low-circuit reading flags an emissions monitoring fault. It usually doesn't change how the car drives, but the sensor or its wiring needs repair and the catalyst monitor won't pass until it's fixed.
Medium
Can I keep driving? Safe to drive short-term — it's an emissions monitoring fault; the car usually drives normally but can fail an emissions test.
Common symptoms
What you'll notice
- Check-engine light on
- Often no noticeable change in how the car drives
- Failed emissions test
- Catalyst-monitor readiness won't complete
Common causes
Most likely first
- Failed catalyst temperature sensor (bank 1, sensor 1)Likely
- Signal wire shorted to ground or open in the sensor circuitCommon
- Loose or corroded connector at the sensorCommon
- ECM fault (rare — verify the sensor and wiring first)Less often
How to diagnose & fix
Work through it in order
- Scan and read freeze-frame data to confirm the fault is the bank 1 sensor 1 catalyst temperature circuit.
- Inspect the sensor connector and wiring near the exhaust for a short to ground, heat damage, or corrosion.
- Back-probe the sensor and compare its resistance/voltage to the temperature specification.
- Check the sensor's ground and reference circuits back toward the ECM.
- Replace the catalyst temperature sensor if it reads out of range with good wiring. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0427?+
Yes, in the short term — it's an emissions monitoring fault, not a driveability hazard. Repair it before an emissions test.
Can I just clear P0427?+
It returns once the ECM re-tests the circuit. The sensor or wiring must be repaired first.
Related codes
Often seen with P0427
Read & clear P0427 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX