P1420 Code: Meaning, Symptoms, Causes & Fix

Overview

P1420 is triggered when monitoring logic identifies an issue with Catalyst Temperature Sensor Failure affecting emissions and air-fuel control.

Symptoms

rough idle under load
failed emissions test readiness
increased fuel consumption

Common causes

Control module logic or calibration issue affecting catalyst temperature sensor failure
Electrical fault in the affected circuit
Connector pin damage/corrosion or harness stress near related components

How to diagnose P1420

Confirm P1420 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to catalyst temperature sensor failure for obvious defects.
Use freeze-frame and live data to isolate whether the issue is electrical, mechanical, or control logic.
Check for related DTCs to identify the root-cause chain before replacing parts.
After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P1420

High: This code is high severity because the affected system can directly impact drivability, safety, or catalyst/engine protection.

Can you drive with P1420?

Driving with P1420 should be limited to a short trip for diagnosis/repair. Continued driving can cause expensive secondary damage.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

Repair obvious wiring/connector faults first to prevent repeat parts replacement.
Address the root fault mode (generic) in the catalyst temperature sensor failure circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify P1420 remains cleared under the conditions that originally set the code.

Fix options

Inspect circuit and connector condition.
Clear code and confirm through drive cycle.
Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$350-$1800

Common mistakes when diagnosing P1420

Replacing parts without verifying voltage, ground, and signal integrity first.
Ignoring related stored/pending codes that indicate upstream faults.
Skipping post-repair verification drive cycle and readiness checks.

P1420 in common vehicles

P1420 appears across makes such as Mazda, Subaru, Lexus, Jeep. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P1420?

P1420 is commonly set by generic faults affecting catalyst temperature sensor failure.

How much does it cost to fix P1420?

For P1420, repair costs are typically $350-$1800 depending on exact root cause, labor rates, and part quality.

Can I clear P1420 without repair?

You can clear P1420 temporarily, but the code usually returns until the underlying fault is corrected.