SPN 94 FMI 4
Fuel Delivery Pressure — Voltage below normal or shorted low.
The sensor circuit voltage is lower than it should ever be, usually near zero.
What the SPN covers: Low-pressure fuel supply pressure feeding the high-pressure pump, after the lift pump and filters. More on SPN 94.
What FMI 4 usually points to: Signal wire shorted to ground, a lost 5 V reference, or an open signal wire on a pulled-down circuit. More on FMI 4.
Severity
HIGH — limit use, diagnose now
Low fuel supply can cause power loss, hard starting and pump damage. Address before working the engine hard.
Likely causes
- Wiring or connector fault in this circuit (most common for electrical FMIs)
- Clogged fuel filter(s)
- Failed or weak lift/transfer pump
- Air leak on the suction side
- Low fuel level or gelled fuel in cold weather
- Faulty pressure sensor
Checks & fixes (easiest first)
- Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins
- Check the reference voltage, ground and signal at the component per OEM pin-out
- Replace fuel filters and prime the system
- Check for air in clear lines or a sight glass
- Measure supply pressure with a mechanical gauge
- Check tank pickup and vent
FAQ
What does SPN 94 FMI 4 mean?
Fuel Delivery Pressure — voltage below normal or shorted low. The sensor circuit voltage is lower than it should ever be, usually near zero.
Is SPN 94 FMI 4 serious?
Low fuel supply can cause power loss, hard starting and pump damage. Address before working the engine hard.
What should I check first for SPN 94 FMI 4?
Inspect the connector and harness for this circuit: corrosion, water, chafing, backed-out pins; Check the reference voltage, ground and signal at the component per OEM pin-out; Replace fuel filters and prime the system.