P040C
EGR Temperature Sensor A Circuit Low
Emissions (EGR)
Generic OBD-II
Medium
What it means
P040C means the ECM sees a lower-than-expected voltage from the "A" exhaust gas recirculation (EGR) temperature sensor. That sensor confirms hot exhaust is actually flowing through the EGR system; when its circuit reads low, the computer flags an emissions monitoring fault. It usually doesn't change how the car drives, but it is a sensor-circuit problem that needs the sensor or wiring repaired.
Medium
Can I keep driving? Safe to drive short-term — it's an emissions monitoring fault; you may notice little change, but the car can fail an emissions test.
Common symptoms
What you'll notice
- Check-engine light on
- Often no noticeable change in how the car drives
- Failed emissions test
- Occasional rough EGR operation or slight loss of economy
Common causes
Most likely first
- Failed EGR temperature sensor ALikely
- Signal wire shorted to ground or open in the sensor circuitCommon
- Loose or corroded connector at the sensorCommon
- Carbon build-up on the sensor affecting its readingLess often
- ECM fault (rare — verify the sensor and wiring first)Less often
How to diagnose & fix
Work through it in order
- Scan and read freeze-frame data to confirm the fault is the EGR temperature sensor A circuit (not EGR flow).
- Inspect the sensor connector and wiring for a short to ground, chafing, or corrosion.
- Back-probe the sensor and compare its resistance/voltage to the temperature specification.
- Remove and check the sensor tip for heavy carbon fouling.
- Replace the EGR temperature sensor if it reads out of range with good wiring. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P040C?+
Yes, in the short term — it's an emissions monitoring fault, not a driveability hazard. Repair it before an emissions test or long-term running.
Can I just clear P040C?+
It will return once the ECM re-tests the circuit. The sensor or its wiring needs to be repaired first.
Related codes
Often seen with P040C
Read & clear P040C 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