P0428

What it means

P0428 means the engine control unit has seen a signal from the catalyst temperature sensor on Bank 1, Sensor 1 (upstream of or at the front of the catalytic converter) that is higher than the expected range. This is usually a voltage that is stuck high, which points to a circuit fault, a sensor fault or a short to voltage rather than a genuinely overheated catalyst. Not every vehicle has a catalyst temperature sensor, so this code is mainly seen on models that use one to monitor catalyst or protect it from overheating.

Symptoms

• Malfunction indicator lamp on
• Possible reduced performance or limp mode on some models if the control unit uses the sensor for catalyst protection
• Rich running or enrichment strategy active on some models, giving poorer fuel economy
• Catalyst monitor or other readiness monitors not completing
• Emissions test failure
• Often no noticeable driveability change

Possible causes

• Faulty catalyst temperature sensor (internal failure giving a high signal)likely
• Signal wire shorted to voltage or to another live circuitlikely
• Damaged, corroded or contaminated sensor connector or terminalslikely
• Heat or physical damage to the sensor wiring harness near the exhaustpossible
• Open circuit on the sensor ground or reference return causing a high readingpossible
• Genuine catalyst overheating from misfire or an over-rich mixturepossible
• Fault in the engine control unit or outdated softwarerare

How to diagnose

1. Read all stored and pending codes plus freeze frame data, and note any misfire, fuel trim or other catalyst-related codes
2. Check for relevant technical service bulletins and confirm from the vehicle's wiring information that this model actually uses a catalyst temperature sensor and where it is fitted
3. Visually inspect the sensor, its wiring and connector for heat damage, chafing, corrosion, water ingress or exhaust leaks
4. Look at live data for the catalyst temperature reading with the engine cold and then warm, and compare it with ambient and expected exhaust temperature
5. Back-probe or disconnect the sensor and check the reference voltage, signal and ground circuits against the manufacturer's specification
6. Test the wiring for shorts to voltage, open circuits and high resistance between sensor and control unit
7. Check the sensor's resistance or output against the specification for this model, as values vary by sensor type
8. Check for misfires or a rich mixture that could genuinely overheat the catalyst before condemning the sensor

How to fix

• Replace the catalyst temperature sensor if it fails its specification checks
• Repair or replace damaged wiring, and clean or renew the faulty connector terminals
• Repair any short to voltage or open circuit found in the signal or ground wiring
• Correct any misfire or rich running condition that is overheating the catalyst, and check the catalyst condition afterwards
• Update the control unit software only if the manufacturer lists an outdated calibration as a known cause for this code on this model

Can I keep driving?

Nearby codes

• P0427GenericCatalyst Temperature Sensor Circuit Low Bank 1 Sensor 1
• P0429GenericCatalyst Heater Control Circuit/Open Bank 1