Coolant Temperature High (EGR Cooler Leak Suspected)
The VOLVO-MACK-MID128-PID110-FMI16 (Volvo/Mack D/MP Series) diesel fault code means: Coolant Temperature High (EGR Cooler Leak Suspected). This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- intermediate
- Estimated cost
- $1,500-$5,500
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Common Symptoms
- Coolant loss with no visible drip
- White steam or sweet smell from exhaust stack
- Coolant level drops between service intervals
- Heater blows cold, cab heat intermittent
- Engine overheat warning or derate
- Check Engine Light illuminated
Probable Causes (Ranked by Likelihood)
- EGR cooler internal leak (major cause on D13/MP8 — coolant entering exhaust) Very Likely
- Head gasket failure or cracked cylinder head (D13/MP8 high-mileage failure mode) Likely
- Failed water pump or slipping drive coupling Possible
- Plugged radiator core or CAC limiting airflow Possible
- Failed ECT sensor reading high Less Likely
Step-by-Step Diagnostic Procedure
Connect Volvo PTT or Mack Guided Diagnostics and capture freeze-frame coolant temp and fuel rate around the fault event.
Pressure-test the cooling system at operating temperature; a dropping gauge with no external leak points to an internal leak.
Perform an EGR cooler isolation (clamp off coolant lines) and re-pressurize — if the leak stops, the EGR cooler is failed.
Combustion-gas test the coolant expansion tank; bubbles or positive test indicates head gasket or cracked head.
Remove the EGR cooler and inspect for coolant wash or staining on the exhaust-side flow path.
If EGR cooler and head test good, verify water pump shaft does not slip under load and that thermostat opens at 180-185 F.
Frequently Asked Questions
What does Volvo/Mack code MID128-PID110-FMI16 mean?
Volvo/Mack code MID128-PID110-FMI16 (Coolant Temperature High (EGR Cooler Leak Suspected)) 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 cooling / EGR cooler 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-PID110-FMI16?
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-PID110-FMI16?
Typical repair falls in the range $1,500-$5,500. 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.