PACCAR · 5-Volt Sensor Supply Voltage 2High

PACCAR SPN 3510 FMI 3: Sensor Supply Voltage High

SPN 3510 FMI 3 (FMI 3) — Sensor Supply Voltage 2 - Voltage Above Normal, or Shorted to High Source

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Quick Answer

SPN 3510 FMI 3 means the second 5-volt reference supply feeding a group of PACCAR sensors has risen above its normal range, usually from a short to a higher voltage source. It is High severity and commonly triggers multiple sensor codes at once, though the engine keeps running.

Overview: PACCAR SPN 3510 FMI 3

SPN 3510 covers Sensor Supply Voltage 2, a separate 5-volt reference circuit from SPN 3509 that the PACCAR MX engine ECM uses to power a different group of analog sensors. FMI 3 flags voltage above normal, meaning the reference has been pulled high rather than pulled low, usually from a short to a stronger voltage source somewhere along that circuit. ProfessionalDieselRepair.com sees shops waste time chasing individual sensor codes on this fault before realizing they're all sourced from the same compromised supply rail.

Repair Snapshot

Time

2 - 4 Hours

Difficulty

Intermediate

Parts Cost

$30 - $250

Dealer Labor

$400+

Tools Required

  • PACCAR Davie4
  • Multimeter
  • Diesel Laptops Diagnostic Software
  • Wiring Repair Kit

What SPN 3510 FMI 3 Means

SPN 3510 FMI 3 means the second 5-volt reference circuit feeding a group of PACCAR MX engine sensors is reading voltage above its normal window, typically from a short to a higher voltage source or an open ground reference. This can cause multiple sensor codes to appear simultaneously since several sensors often share this supply circuit. It sets the MIL and can push affected sensor readings to default or maxed-out values.

Symptoms Drivers Notice

  • Multiple unrelated sensor fault codes appearing together
  • MIL illuminated
  • Erratic readings on sensors sharing the affected supply circuit
  • Possible rough idle or throttle response issues depending on which sensors are affected

Most Likely Root Causes

Chafed sensor harness shorting to a higher voltage circuit

Common

Any wire on the shared 5-volt bus rubbing against a battery-fed or ignition-fed wire will pull the whole reference circuit above its normal range.

Open ground reference on the sensor supply circuit

Common

A broken or corroded ground connection can cause the reference voltage to float higher than expected on some sensor supply designs.

Internally shorted sensor

Occasional

A sensor with a failed internal circuit board can short its 5-volt supply pin to a higher voltage source internally.

ECM internal regulator fault

Rare

The ECM's own 5-volt regulator stage can fail, but this should only be suspected after every sensor on the circuit has tested clean.

Common Misdiagnoses (Don't Waste Parts)

Replacing sensors one by one hoping to find the bad one

Why it happens: A parts-cannon approach swaps components without ever measuring the actual supply voltage first.

Do this instead: Measure the 5-volt reference directly at the ECM first, then isolate sensors by unplugging them one at a time while watching the voltage.

Condemning the ECM immediately

Why it happens: Multiple simultaneous sensor codes look like a control module failure to techs unfamiliar with shared supply circuits.

Do this instead: Rule out every sensor and harness section on that supply group before ever suspecting the ECM's internal regulator.

Only checking the sensor that threw the most recent code

Why it happens: Techs assume the freshest code points directly to the fault location.

Do this instead: Pull the full active fault list and cross-reference every SPN tied to the same sensor supply circuit before starting diagnosis.

Master Tech Commentary

Mechanic's Notes

Shop tip from ProfessionalDieselRepair.com: don't chase individual sensor codes one at a time on this fault. PACCAR wires multiple sensors off shared 5-volt supply circuits, and a single short anywhere on that bus explains every sensor code on the same circuit at once. Pull the wiring diagram before you start unplugging things.

Step-by-Step Diagnostic Procedure

  1. Step 1: Pull codes with PACCAR Davie4 and note every SPN that shares the 3510 sensor supply circuit to narrow down which sensor group to inspect.
  2. Step 2: With the key on and engine off, back-probe the sensor supply wire at the ECM connector and verify you have 4.9-5.1 volts DC rather than an elevated reading.
  3. Step 3: Check for a chafed wire shorting the 5-volt supply to a higher-voltage circuit such as battery power, which would explain the voltage-above-normal condition.
  4. Step 4: Unplug sensors on that supply circuit one at a time while monitoring the reference voltage to isolate which sensor or harness leg is causing the fault.
  5. Step 5: Repair or replace the damaged harness section, reconnect all sensors, and confirm 5.0 volts is restored before clearing codes.

Live Data & Freeze-Frame Tips

Back-probe the 5-volt supply wire at the ECM with the key on and watch it on a multimeter while you disconnect sensors one at a time - a clean drop back to 5.0 volts the instant you unplug a specific sensor confirms that circuit leg as the fault.

Safety Warnings

  • Turn the ignition off before disconnecting sensor connectors to avoid setting additional false codes.
  • Use a fused test lead when back-probing to avoid accidentally shorting the circuit yourself.
  • Keep hands clear of moving belts and fans when tracing harnesses along the front of the engine.
  • Wear gloves when working with connectors that may have fuel or oil contamination.

When to Limp In vs Tow

Towing is rarely necessary for this code alone since the engine typically continues to run on default sensor values. Consider towing if critical sensors like coolant temperature or oil pressure are affected and warning signs of overheating or low oil pressure appear.

Prevention Tips for Fleets & Owner-Operators

  • Route sensor harnesses away from higher-voltage wiring during any chassis or engine service.
  • Dielectric-grease all sensor connectors when reassembling after maintenance work.
  • Address minor sensor codes early before a chafe point progresses to a full short.
  • Inspect low-mounted sensor connectors for water intrusion after driving through deep water.

Related Fault Codes

SPN 3509 FMI 4

Sensor Supply Voltage 1 running low, a related but separate 5-volt reference circuit on the same engine.

SPN 3510 FMI 4

Same supply circuit but voltage below normal instead of above, typically a short to ground rather than a short to power.

SPN 91 FMI 3

Accelerator pedal position sensor voltage high, one of the sensors that can share a 5-volt supply circuit.

Frequently Asked Questions

Can I drive with SPN 3510 FMI 3 active?

You can typically still drive, but expect the ECM to fall back on default values for any sensor sharing that supply circuit, which can cause rough idle or hesitation depending on which sensors are affected.

How do I reset SPN 3510 FMI 3 without a scanner?

A battery disconnect can sometimes clear it temporarily, but the code returns immediately once the ECM re-checks the 5-volt supply on the next key cycle if the short hasn't been repaired.

Does this code cause an active derate?

It doesn't trigger the aggressive emissions-related derate seen with aftertreatment faults, but a bad sensor reading on the same circuit can indirectly cause the ECM to limit power for safety.

Why do I have multiple sensor codes at once from one wiring problem?

PACCAR wires multiple sensors off shared 5-volt reference circuits, so a single short anywhere on that bus can push the voltage out of range for every sensor connected to it simultaneously.

Is this the same as a bad alternator or charging system issue?

No, this is specifically about the regulated 5-volt sensor reference the ECM creates internally, not the 12 or 24-volt chassis battery system.

Can a mechanic find this without a wiring diagram?

It's much faster and more reliable with the OEM wiring diagram loaded in Davie4 or Diesel Laptops, since it shows exactly which sensors share the affected supply circuit rather than guessing.