What Does P042B Mean?
The catalyst temperature sensor on bank 1, sensor 2 (post-catalyst) is not performing within the expected range. The sensor's readings do not correlate with current engine operating conditions — it may be responding too slowly, reading an implausible temperature relative to the pre-cat sensor, or showing values that don't change as expected during load transitions. The driver will see the check engine light and may experience conservative PCM operating strategies.
Common Causes
35%
Degraded catalyst temperature sensor 2 with slow response or calibration drift
25%
Soot or carbon deposits on the sensor probe reducing thermal conductivity
15%
High-resistance wiring connection causing voltage reading errors
15%
Catalytic converter itself malfunctioning, causing unexpected outlet temperatures
10%
Aftermarket or incorrect replacement sensor with wrong calibration
Diagnostic Steps
1
Monitor both the pre-cat (sensor 1) and post-cat (sensor 2) temperature PIDs simultaneously. Under normal operation, the post-cat should read higher than the pre-cat by 50-100°F due to catalytic reactions. If sensor 2 reads lower or shows erratic behavior, it is suspect.
2
With the engine at steady 2500 RPM, observe the post-cat temperature sensor response. It should show a gradual, smooth temperature curve. Erratic fluctuations, flat readings, or extreme values point to sensor degradation.
3
Remove the sensor and inspect the probe tip for heavy carbon buildup. Clean with a brass brush and non-chlorinated brake cleaner, or replace if the probe is visibly damaged.
4
Check the wiring harness for high-resistance connections by measuring voltage drop across each wire in the sensor circuit with the sensor connected and the engine running. More than 0.1V drop indicates a wiring issue.
5
Verify the correct OEM part number was used for the sensor. Cross-reference the sensor's resistance-temperature curve with factory specifications.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The catalyst temperature sensor on bank 1, sensor 2 (post-catalyst) is not performing within the expected range. The sensor's readings do not correlate with current engine operating conditions — it may be responding too slowly, reading an implausible temperature relative to the pre-cat sensor, or sh...
The most common cause of P042B (Catalyst Temperature Sensor Circuit Range/Performance (Bank 1 Sensor 2)) is: Degraded catalyst temperature sensor 2 with slow response or calibration drift
Typical repair costs for P042B range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with moderate caution. If the post-cat temperature sensor is reading inaccurately, the PCM may not detect overheating of the catalytic converter. Avoid heavy load conditions and towing until the sensor is verified or replaced.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P042B to identify the root cause.
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Quick Info
Category
Powertrain
System
Catalytic Converter / Exhaust System
Difficulty
Type
Generic (SAE)
Recommended Tools
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