What P0428 means
P means powertrain (engine and transmission). The 0 marks a generic code defined by SAE, so the same number means the same thing across makes. The third character, 4, places it in the auxiliary emission controls subsystem; the last two digits identify the specific fault.
Some vehicles measure catalytic converter temperature directly with a high-temperature sensor, used to protect the converter from overheating and to manage warm-up.
Bank 1 is the side of the engine that contains cylinder 1. Inline engines have only bank 1, so a bank 2 code on an inline engine usually indicates a manufacturer-specific use.
Sensor 1 is the one upstream of the catalytic converter, closest to the engine.
What “Circuit High” means here
"High" means the signal or control voltage rose above the maximum the module expects. On a temperature sensor of this type (a thermistor fed from a 5 V reference through a resistor in the module), high signal voltage reads as a very low temperature, often the bottom of the scale. The usual explanations are an open circuit — an unplugged or corroded connector, a broken wire — or an open sensor.
What you may notice
Symptoms depend on the vehicle and on how the module responds to the fault. Any of these can accompany P0428:
- Usually none
- Over-temperature protection behaving differently
Where to start diagnosing P0428
- Inspect the sensor connector and wiring for heat damage.
- On a cold vehicle, the reading should be near ambient.
- Compare with specification for resistance at a known temperature.
Clear the code only after recording freeze frame data: it shows the engine speed, load and temperature at the moment the fault set, which is often the best clue to reproducing it.
Live data to watch
These standard OBD2 values relate to P0428. Support varies by vehicle; a value your car does not report will simply be missing.
| Value | What to look for |
|---|---|
| Catalyst temperature (PIDs 0x3C–0x3F) | Should rise steadily after start and remain plausible. |
Related codes
Codes from the same catalyst temperature sensor family. If several are stored together, the shared part — wiring, a common reference voltage, or the component itself — is the place to start.
| Code | Definition |
|---|---|
| P0425 | Catalyst Temperature Sensor (Bank 1 Sensor 1) |
| P0426 | Catalyst Temperature Sensor Range/Performance (Bank 1 Sensor 1) |
| P0427 | Catalyst Temperature Sensor Low (Bank 1 Sensor 1) |
| P0435 | Catalyst Temperature Sensor (Bank 2 Sensor 1) |
| P0436 | Catalyst Temperature Sensor Range/Performance (Bank 2 Sensor 1) |
| P0437 | Catalyst Temperature Sensor Low (Bank 2 Sensor 1) |
| P0438 | Catalyst Temperature Sensor High (Bank 2 Sensor 1) |
Further reading
Frequently Asked Questions
What does P0428 mean?
P0428 is the generic SAE J2012 code for "Catalyst Temperature Sensor High (Bank 1 Sensor 1)". In plain terms, it means the engine computer has detected a "circuit high" fault on the catalyst temperature sensor.
Can I keep driving with P0428?
Usually drivable; have it diagnosed so converter protection works.
What should I check first for P0428?
Inspect the sensor connector and wiring for heat damage.
Definition source: SAE J2012 / ISO 15031-6 generic DTC definitions. This is the generic meaning that applies across makes; a manufacturer can define a code more narrowly or add its own sub-codes, so confirm against the service information for your vehicle before replacing parts. Written by the OBDAssistant engineering team — see our editorial policy.