What Does P042C Mean?
The catalyst temperature sensor located after the catalytic converter on bank 1 (sensor 2) is reporting a voltage that is below the expected range. This indicates a potential short to ground, open circuit, or failed sensor. The driver may not notice any driveability symptoms, but the MIL will be illuminated and emissions testing will fail.
Common Causes
35%
Failed catalyst temperature sensor (internal short to ground)
30%
Damaged or corroded wiring/connector to the sensor
20%
Short to ground in the sensor signal circuit
10%
PCM/ECM internal fault on the sensor input circuit
5%
Exhaust system damage routing heat or moisture to the sensor wiring
Diagnostic Steps
1
With KOEO, backprobe the catalyst temperature sensor connector and measure the signal voltage — it should read approximately 0.5–4.5V depending on temperature; a reading below 0.2V confirms the low circuit condition.
2
Disconnect the sensor connector and measure resistance across the sensor terminals — compare to the manufacturer's resistance vs. temperature chart (typically 100–300 ohms at operating temperature).
3
With the sensor disconnected, check for 5V reference voltage at the harness connector between the reference pin and ground pin; absence indicates a wiring or PCM issue.
4
Inspect the wiring harness from the sensor to the PCM for chafing, melting, or corrosion — pay special attention to areas near exhaust components where heat damage is common.
5
If wiring and sensor test OK, swap the sensor with a known-good unit and clear the code to verify the repair.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
The catalyst temperature sensor located after the catalytic converter on bank 1 (sensor 2) is reporting a voltage that is below the expected range. This indicates a potential short to ground, open circuit, or failed sensor. The driver may not notice any driveability symptoms, but the MIL will be ill...
The most common cause of P042C (Catalyst Temperature Sensor Circuit Low (Bank 1 Sensor 2)) is: Failed catalyst temperature sensor (internal short to ground)
Typical repair costs for P042C range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive in most cases. The vehicle will continue to operate normally, but emissions performance is unmonitored for this sensor. Repair before next emissions test.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P042C to identify the root cause.
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Quick Info
Category
Powertrain
System
Exhaust / Catalytic Converter
Difficulty
Type
Generic (SAE)
Recommended Tools
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