Catalyst Temperature Sensor High (Bank 1)
The P0428 code means the vehicle's onboard diagnostic system has detected: Catalyst Temperature Sensor High (Bank 1). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $80 - $400 (parts and labor)
Reads enhanced codes and shows real-time O2 sensor data. Verify the cat is actually bad before dropping $1,000+ on a replacement.
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Common Symptoms
- Check Engine Light illuminated
- Scan tool shows abnormally high catalyst temperature
- Possible overheating warning
- No drivability issues in most cases
Probable Causes (Ranked by Likelihood)
- Faulty catalyst temperature sensor reading high Very High
- Short to voltage in sensor signal wire High
- Open ground wire causing signal to float high Moderate
- Actually overheating catalyst due to misfire or rich condition Moderate
Step-by-Step Diagnostic Procedure
-
Compare scan tool catalyst temperature to an infrared thermometer reading at the converter
-
Check if the temperature reading is plausible -- readings above 1800 degrees F likely indicate a sensor or wiring fault
-
Verify sensor ground wire has good continuity to the ECM
-
Check signal wire for short to a voltage source
-
If readings appear accurate, check for misfires or rich fuel condition causing genuine catalyst overheating
Frequently Asked Questions
Can I drive with code P0428?
Drive short distances only until diagnosed. While a faulty sensor is the most common cause, if the catalyst is genuinely overheating due to a misfire, continued driving can cause a fire hazard or catalyst meltdown.
How do I know if the catalyst is really overheating?
Use an infrared thermometer to check the actual converter temperature. If it matches the scan tool reading and exceeds 1400 degrees F, there is a genuine overheating condition that needs immediate attention.
What causes a catalytic converter to overheat?
Engine misfires, extremely rich fuel mixture, or a deteriorating catalyst substrate can cause overheating. Unburned fuel enters the converter and ignites, raising temperatures to dangerous levels.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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