What it means
Catalyst temperature sensor at bank 2 sensor 1 above upper plausibility — open signal or short to B+.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 Sensor 1 measures catalyst temperature for the control module. P0438 sets when the circuit signal is higher than the module's plausible range, often because the signal wire is open or shorted to battery voltage.
Common causes
Most likely first.
- Open signal line
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Review freeze-frame and live data to confirm Bank 2 Sensor 1 is reporting an abnormally high or fixed reading.
- Inspect the Bank 2 Sensor 1 harness for breaks, melted insulation, or pinching against a power source.
- Check the connector for corrosion, loose fit, or pushed-back terminals that could interrupt the signal.
- Use the manufacturer's wiring diagram to test the signal circuit for an open or short to battery voltage and verify the relevant supply and ground paths.
- If the harness and connector pass, test Bank 2 Sensor 1 to specification before suspecting a control-module fault.
Common fixes
- Repair an open signal wire in the Bank 2 Sensor 1 circuit.
- Repair wiring shorted to battery voltage near Bank 2 Sensor 1.
- Restore secure, clean connector terminal contact.
- Replace Bank 2 Sensor 1 if it fails the specified test with sound wiring.
Can I keep driving?
The vehicle is generally driveable if it runs normally, but catalyst temperature monitoring may be incorrect and emissions testing can fail. Avoid heavy load if a strong sulfur smell is present, and fix the open or high-voltage circuit fault soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.