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?
- Short distances only
- 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
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.
What actually makes the computer set this EGR code?
California's heavy-duty OBD regulation sets the low-flow trip point where a decrease from the manufacturer's specified EGR rate would push NMHC, CO or NOx past 2.0 times the applicable standards, or PM past the standard plus 0.02 g/bhp-hr (Title 13 CCR 1971.1, section (e)(3.2.1)). Note the second route: it must also flag the case where the EGR system has hit its control limits and simply cannot reach the commanded flow — so this code can set with the valve working and the system still unable to deliver. This threshold comes from the heavy-duty OBD regulation, which covers 2010 and later heavy-duty engines. If your engine is in a pickup at or under 14,000 lb GVWR it is certified under the separate medium-duty rule instead, so treat this as the design intent rather than your engine's exact limit.
Mechanics Guide Step-by-step diagnosis
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.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1971.1 (Heavy-Duty OBD)malfunction criteria, section (e)
Commonly Affected Vehicles
- Volvo VNL 760/860 with D13
- Volvo VNR 640 with D13
- Mack Anthem with MP8
- Mack Pinnacle with MP8
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