What Does P0428 Mean?
The catalyst temperature sensor on bank 1, sensor 1 is reporting a voltage above the maximum expected threshold. This typically indicates an open circuit — the signal wire is disconnected, the thermistor is open, or a ground wire is broken. The PCM pulls the signal line high through an internal pull-up resistor when the circuit is open. The driver will see the check engine light and the PCM may enter a protective reduced-power mode to prevent potential catalyst overheating.
Common Causes
35%
Open circuit in the catalyst temperature sensor (failed thermistor element)
30%
Disconnected or broken wiring between the sensor and PCM
20%
Corroded or backed-out terminal pins causing open connection
10%
Open ground circuit preventing sensor current flow
5%
Sensor wire melted/broken from excessive exhaust heat exposure
Diagnostic Steps
1
Check the scan tool PID for catalyst temperature sensor 1. A reading at or near the maximum scale (often showing 5V or an extremely high temperature) confirms an open/high circuit.
2
Inspect the sensor connector for full engagement. Ensure the latch is secure and pins are not receded or spread. A poor connection at this high-temperature location is very common.
3
Disconnect the sensor and measure thermistor resistance. At room temperature expect 50K-200K ohms. An OL (infinite) reading confirms a failed open sensor element.
4
If the sensor is good, check continuity of both the signal and ground wires from the sensor connector all the way to the PCM connector. Use the vehicle wiring diagram to identify the correct PCM pins.
5
Inspect the harness for thermal damage in the area between the exhaust manifold and firewall. Replace damaged sections with high-temperature-rated wiring and protective loom.
Estimated Repair Cost
$90 - $350
Parts + labor, varies by vehicle and location
The catalyst temperature sensor on bank 1, sensor 1 is reporting a voltage above the maximum expected threshold. This typically indicates an open circuit — the signal wire is disconnected, the thermistor is open, or a ground wire is broken. The PCM pulls the signal line high through an internal pull...
The most common cause of P0428 (Catalyst Temperature Sensor High Input (Bank 1 Sensor 1)) is: Open circuit in the catalyst temperature sensor (failed thermistor element)
Typical repair costs for P0428 range from $90 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with caution. Without accurate catalyst temperature data, the PCM may assume the worst-case scenario and enter reduced power mode, or it may fail to detect actual overheating. Avoid sustained high-load driving and towing until repaired.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0428 to identify the root cause.
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Quick Info
Category
Powertrain
System
Catalytic Converter / Exhaust System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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