SPN 102 FMI 3 — Boost Pressure Sensor — Voltage High
The intake-manifold boost (MAP) pressure sensor signal is reading above its normal voltage range — usually a sensor, wiring, or short fault rather than true overboost. The ECM may limit fueling/boost, causing low power until it's resolved.
Your SPN/FMI rides along, so nearby mechanics see the fault before they quote you.
How serious is it?
Caution. Limp to the next safe stop.
Most likely causes
- Short-to-voltage or chafed wiring on the boost-sensor signal circuit
- Failed boost/MAP pressure sensor
- Connector corrosion or a backed-out pin at the sensor
- Soot/oil contamination fouling the sensor element
First moves (roadside)
- Inspect the boost-sensor connector and pigtail for corrosion, oil, or chafe.
- Compare commanded vs. actual boost in the data — a flat or pegged reading points to the sensor circuit.
- Check for a short-to-power on the signal wire before replacing the sensor.
- Clean or replace the sensor if the element is fouled with oil/soot.
Common misdiagnoses
- Chasing a turbo or wastegate problem when the sensor circuit is simply shorted high.
- Replacing the sensor without checking the harness for a short-to-voltage.
- Ignoring low-power complaints that are really this sensor limiting fuel.
FAQ
The intake-manifold boost (MAP) pressure sensor signal is reading above its normal voltage range — usually a sensor, wiring, or short fault rather than true overboost. The ECM may limit fueling/boost, causing low power until it's resolved.
Caution — Limp to the next safe stop.
The most common cause is: Short-to-voltage or chafed wiring on the boost-sensor signal circuit. Other possibilities include Failed boost/MAP pressure sensor; Connector corrosion or a backed-out pin at the sensor; Soot/oil contamination fouling the sensor element.
Limp to the next safe stop. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Find a mechanic or related guides
General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.