DEF Doser/Injector Circuit Shorted
The VOLVO-MACK-MID128-PID3361-FMI6 (Volvo/Mack D/MP Series) diesel fault code means: DEF Doser/Injector Circuit Shorted. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- advanced
- Estimated cost
- $500-$2,500
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Common Symptoms
- DEF warning lamp illuminated
- Countdown to engine derate (usually 50 hours)
- Low DEF or poor DEF quality messages
- SCR efficiency low (NOx emissions up)
- 5 mph limp mode if ignored past countdown
Probable Causes (Ranked by Likelihood)
- Failed DEF pump, doser, heater, or sensor in DEF supply module Likely
- Harness damage at DEF tank module (common from road debris) Likely
- DEF line ice blockage (if tank heater failed) Possible
- Contaminated DEF causing pump or doser fouling Possible
- ACM (Aftertreatment Control Module) fault Less Likely
Step-by-Step Diagnostic Procedure
Connect Volvo PTT or Mack Guided Diagnostics, verify MID128-PID3361-FMI6 active, and observe DEF pump and doser live data.
Command DEF pump pressure test; pressure should reach 70-130 psi in a few seconds.
Inspect DEF lines for kinks, leaks, or frozen/clogged sections.
Measure heater element resistance at DEF tank module; replace if open.
Check DEF quality with a refractometer; replace contaminated DEF.
After repair, run the SCR initialization and purge sequence via PTT or Guided Diagnostics.
Frequently Asked Questions
What does Volvo/Mack code MID128-PID3361-FMI6 mean?
Volvo/Mack code MID128-PID3361-FMI6 (DEF Doser/Injector Circuit Shorted) is a serious-severity diagnostic trouble code set on D11/MP7, D13/MP8, and D16/MP10 diesel engines in Volvo VNL/VNR and Mack Anthem/Pinnacle/Granite/Titan trucks. It indicates a fault in the DEF doser system and should be read with Volvo Premium Tech Tool (PTT) or Mack Guided Diagnostics.
Can I drive a Volvo or Mack truck with code MID128-PID3361-FMI6?
Short distances may be acceptable to reach a repair facility, but the fault will escalate to derate (typically 55 mph then 5 mph on aftertreatment faults). Do not defer diagnosis beyond a shift.
How much does it cost to fix Volvo/Mack code MID128-PID3361-FMI6?
Typical repair falls in the range $500-$2,500. Sensor/wiring repairs are at the low end; EGR cooler, NOx sensor set, DEF pump, injector, or head work runs at the high end. Volvo PTT or Mack Guided Diagnostics is normally required for calibration and parameter programming.
Sources
This page is built from documented references. Verify against your own service info before repair work.