What is CAT Code 4377-12 & How to Solve It?

What is CAT Code 4377-12:

CAT Code 4377-12 refers to a fault in the Aftertreatment DEF Dosing Valve circuit — specifically, an electrical fault such as shorted, open, or intermittent voltage.

This code appears when the DEF dosing valve is not receiving proper electrical signals, which prevents it from injecting DEF correctly. If not resolved, it will lead to failed regenerations and possible engine derate.

‍

Why This Happens

• Shorted or broken wiring to the dosing valve.
• Faulty DEF dosing valve solenoid.
• Corroded or loose connector pins.
• Power or ground supply failure to the circuit.
• Internal ECM circuit issue.

‍

How to Fix It

1. Inspect the DEF dosing valve wiring harness for damage.
2. Test for continuity, voltage, and ground at the valve connector.
3. Check for corrosion on terminals and clean or repair as needed.
4. Replace the DEF dosing valve if solenoid resistance is out of spec.
5. Clear the fault and test DEF injection operation under regen.

‍

How to Avoid It Before It Happens

1. Include wiring inspection during every aftertreatment service.
2. Use sealed connectors and protect them from vibration or fluid exposure.
3. Track dosing valve cycle counts and schedule replacement at manufacturer-suggested intervals.
4. Avoid pulling harnesses during other maintenance.