DEF Quality Sensor Circuit Malfunction (Generic)
The P4063 code means the vehicle's onboard diagnostic system has detected: DEF Quality Sensor Circuit Malfunction (Generic). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $150 - $500 (parts and labor)
Best-selling code reader on Amazon. Reads and clears check engine codes on any 1996+ vehicle. Under $30.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Essential for diagnosing sensor codes, checking voltage, and testing circuits. Under $15 and pays for itself on the first job.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light on
- DEF quality warning message
- SCR system may reduce operation
- Speed derate countdown possible
- DEF quality reading invalid
Probable Causes (Ranked by Likelihood)
- Failed DEF quality sensor Very High
- Contaminated DEF affecting sensor High
- Sensor connector corrosion from DEF exposure Moderate
- Wiring fault in DEF tank assembly Low
Step-by-Step Diagnostic Procedure
-
Check DEF quality with refractometer
-
Test DEF quality sensor output
-
Inspect sensor connector for DEF contamination
-
Verify DEF tank module wiring
Frequently Asked Questions
How do I check DEF quality?
Use a DEF refractometer, available for about $30. DEF should read 32.5% urea concentration.
Can bad DEF damage my truck?
Yes, contaminated DEF can damage the SCR catalyst, DEF injector, and DEF pump.
Can I drive with P4063?
You can drive short distances. If the DEF is bad, drain the tank and refill with fresh certified DEF.
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.