DEF Pump Circuit Open (Generic)
The P4066 code means the vehicle's onboard diagnostic system has detected: DEF Pump Circuit Open (Generic). This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- hard
- Estimated cost
- $300 - $900 (parts and labor)
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Common Symptoms
- Check Engine Light on
- No DEF delivery to SCR
- Speed derate countdown active
- DEF system fault
- Complete SCR shutdown
Probable Causes (Ranked by Likelihood)
- Open circuit in DEF pump wiring Very High
- Failed DEF pump motor High
- Blown DEF pump fuse or relay Moderate
- PCM pump driver failure Low
Step-by-Step Diagnostic Procedure
-
Check DEF pump fuse and relay
-
Test pump motor resistance
-
Inspect wiring between pump and PCM
-
Verify power supply to DEF pump
Frequently Asked Questions
What does the DEF pump do?
The DEF pump pressurizes the diesel exhaust fluid and delivers it to the dosing valve.
Can I drive with P4066?
No, without the DEF pump the SCR system is completely disabled.
How much is a DEF pump?
DEF pumps cost $300-700. With labor, expect $500-900 total.
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