DEF Doser/Injector Circuit Open
What does VOLVO-MACK-MID128-PID3361-FMI5 mean?
The VOLVO-MACK-MID128-PID3361-FMI5 (Volvo/Mack D/MP Series) diesel fault code means: DEF Doser/Injector Circuit Open. This is a serious severity code.
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-FMI5 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-FMI5 mean?
Volvo/Mack code MID128-PID3361-FMI5 (DEF Doser/Injector Circuit Open) 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-FMI5?
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-FMI5?
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.