P2478
Exhaust Gas Temperature Out of Range Bank 1 Sensor 1
Auxiliary emissions (exhaust temperature)
Generic OBD-II
Low
What it means
P2478 means exhaust gas temperature (EGT) sensor 1 on bank 1 is reporting a value the ECM considers out of the reasonable range — too high, too low, or not matching conditions. The ECM relies on this reading to protect the catalyst and, on diesels, manage particulate-filter regeneration. The engine runs normally; the issue is usually a failing sensor or its wiring rather than a mechanical fault.
Low
Can I keep driving? Yes — the car drives normally; this is an exhaust-temperature reading fault, not a running problem.
Common symptoms
What you'll notice
- Check-engine light on
- Usually no change in how the car drives
- Possible disruption to DPF regeneration on diesels
- May fail an emissions/readiness test
Common causes
Most likely first
- Faulty exhaust gas temperature (EGT) sensor 1 on bank 1 reading an implausible valueLikely
- Wiring open, shorted, or high-resistance in the sensor circuitCommon
- Corroded or loose sensor connectorCommon
- Heat-damaged harness near the exhaustLess often
- Faulty ECM/PCM input (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and compare the reported EGT value to expected exhaust temperature.
- Inspect EGT sensor 1 on bank 1 and its connector for corrosion, heat damage, or a loose fit.
- Check the circuit for continuity and for shorts to power or ground.
- Measure the sensor's resistance against spec; replace it if the value is out of range.
- Clear the code and re-drive; if the reading is still out of range with wiring good, replace the sensor.
FAQ
Quick answers
Is it safe to drive with P2478?+
Yes for normal driving. The sensor reports exhaust temperature for emissions and catalyst protection, so repair it promptly to keep that monitoring accurate.
Can I just clear P2478?+
You can, but if the sensor keeps reading out of range the code comes back. Fix the sensor or wiring first.
Related codes
Often seen with P2478
Read & clear P2478 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX