P2064
Reductant/Regeneration Supply Control Circuit High
Emissions (SCR / DEF after-treatment)
Generic OBD-II
Medium
What it means
P2064 means the control circuit that runs the reductant (DEF) supply and regeneration system is reading an abnormally high voltage, typically an open or short-to-power. The engine starts and runs normally, but the SCR system can't deliver DEF as intended, so NOx rises and many diesels begin a derate countdown. It usually traces to wiring, a connector, or the supply pump/module.
Medium
Can I keep driving? The engine runs and starts normally, but the SCR supply system isn't working right and some diesels derate power — get it fixed promptly.
Common symptoms
What you'll notice
- Check-engine light on
- SCR / diesel-exhaust-fluid (DEF) system warning
- Higher NOx emissions; may fail an emissions test
- Speed / power derate if the fault persists (varies by vehicle)
Common causes
Most likely first
- Reductant supply / regeneration control circuit open or shorted to power (reads high)Likely
- Faulty DEF supply pump or metering/supply control unitCommon
- Corroded or loose connector in the supply control circuitCommon
- Wiring damage in the reductant supply harnessLess often
- Dosing control module / PCM fault (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for companion supply codes (P2062, P2063).
- Inspect the supply control connector and wiring for opens, corrosion, or a short to voltage.
- Test the DEF supply pump/actuator command and feedback with a scan tool.
- Replace the faulty supply component or repair the wiring, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2064?+
The engine drives normally, but the SCR system can't supply DEF correctly and many diesels start a derate countdown. Repair it before the vehicle limits power.
Can I just clear P2064?+
It returns until the supply circuit or component is repaired, and clearing won't stop an emissions derate from recurring.
Related codes
Often seen with P2064
Read & clear P2064 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