P0438Catalyst Temperature Sensor High Input (Bank 2)
The Bank 2 catalyst temperature sensor signal voltage has climbed above its normal operating range.
Definition
The PCM flags P0438 when the Bank 2 catalyst temperature sensor signal exceeds its maximum plausible threshold — most commonly because the circuit is open and the reference pull-up drives the signal high, or because the wire is shorted to voltage. Catalyst temperature monitoring on Bank 2 is suspended and the MIL illuminates. There are no driveability symptoms, but the vehicle will fail emissions testing, and on diesels the fault can interfere with aftertreatment temperature management.
Common causes
- Open sensor element from repeated heat cycling
- Broken signal or return wire near the heat-stressed exhaust section
- Disconnected, corroded, or backed-out connector terminal
- Signal wire shorted to a voltage feed
- ECM input circuit fault (rare)
Common misdiagnoses
- Bank 2 converter replaced for a circuit-high electrical fault
- Sensor replaced when a broken wire or loose terminal is the cause
- Both banks' sensors replaced when only the Bank 2 circuit is open
Troubleshooting steps
1.Compare bank PIDs on a warm engine
A Bank 2 reading stuck at its default or maximum while Bank 1 reads several hundred degrees confirms an electrical open, not a temperature event.
2.Jumper the harness connector
Bridge the two harness terminals with the sensor unplugged; if the PID swings to the opposite extreme, wiring and ECM are proven good and the sensor is open.
3.Check wire continuity to the ECM
Measure end-to-end resistance on both circuit wires; more than a few ohms indicates a break or a failing crimp or terminal.
4.Inspect connectors and heat-exposed wiring
Look for terminals pushed out of the connector cavity and insulation embrittled by exhaust heat on the Bank 2 side.
5.Measure the sensor element
An OL reading across the sensor at room temperature confirms the element has failed open.