What Does P0438 Mean?
The catalyst temperature sensor circuit on bank 2, sensor 1, is reading above the maximum expected voltage. This typically indicates an open circuit, high resistance in the sensor circuit, or a sensor failure causing an artificially high reading. The PCM sets this code when the signal voltage exceeds the calibrated maximum. The MIL will illuminate but driveability is usually unaffected.
Common Causes
35%
Open circuit in the catalyst temperature sensor (failed element)
25%
Broken or disconnected signal wire causing open circuit
20%
Corroded or spread connector terminals creating high resistance
12%
Signal wire shorted to 5V reference or other voltage source
8%
Poor ground connection for the sensor circuit
Diagnostic Steps
1
Verify the sensor signal reads near or at 5V on the scan tool — this confirms the high circuit condition consistent with an open sensor or wiring.
2
Disconnect the sensor connector and measure resistance across the sensor terminals — an open-loop (OL/infinite) reading confirms the sensor has failed internally.
3
With the sensor disconnected, jumper the signal and ground pins at the harness connector — the scan tool reading should drop to minimum if the wiring is intact back to the PCM.
4
Inspect the connector for backed-out pins, corrosion, or terminals that have lost spring tension — these can create intermittent open circuits.
5
Check the sensor ground wire for continuity back to the PCM ground — resistance should be less than 1 ohm.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
The catalyst temperature sensor circuit on bank 2, sensor 1, is reading above the maximum expected voltage. This typically indicates an open circuit, high resistance in the sensor circuit, or a sensor failure causing an artificially high reading. The PCM sets this code when the signal voltage exceed...
The most common cause of P0438 (Catalyst Temperature Sensor Circuit High (Bank 2, Sensor 1)) is: Open circuit in the catalyst temperature sensor (failed element)
Typical repair costs for P0438 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. The catalyst temperature monitoring function is disabled, but engine operation and safety are not affected. Repair to restore full emissions monitoring capability.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0438 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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