P0438 - Catalyst Temperature Sensor High Input (Bank 2, Sensor 1)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0438 is stored when the Engine Control Module (ECM/PCM) detects an abnormally high voltage signal from the catalyst temperature sensor circuit for Bank 2, Sensor 1. The sensor is typically an NTC (Negative Temperature Coefficient) thermistor. A 'High Input' fault usually signifies an open circuit or a broken wire, causing the signal voltage to stay at the reference level (typically 5V) because there is no path to ground through the sensor's resistance. This monitoring is essential to prevent catalyst overheating and to ensure emissions compliance.
Possible Causes
Open circuit in wiring or damaged connector
Faulty catalyst temperature sensor (internal open circuit)
Corrosion in ground points or ECM terminals
Faulty Engine Control Module (PCM/ECU)
Symptoms
Recommended Solution
- Visual Inspection: Check wiring and connectors for Bank 2, Sensor 1 for heat damage, fraying, or corrosion.
- Voltage Test: Disconnect the sensor and measure voltage with IG ON. You should see approx. 5V reference from the PCM. If 0V, trace wiring back to PCM.
- Resistance Test: Measure sensor resistance with a multimeter. An infinite (O.L) reading indicates an internal open circuit. Normal values vary but typically range from 100-500 Ohms when hot (check service manual).
- Simulation: Carefully bridge the connector terminals; if the code changes to P0437 (Low Input), the wiring is intact and the sensor is faulty.
- Component Replacement: Replace the temperature sensor if readings are out of spec.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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