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Glow Plug Circuit Fault Cold Weather No Start: Diagnosis and Fix Order

SPN 1267 FMI 3 (FMI 3) — Engine Glow Plug 1 Circuit - Voltage Above Normal or Shorted to High Source

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Quick Answer

SPN 1267 FMI 3 means a glow plug circuit has high voltage or a short. In cold weather the engine cranks but will not fire. Test each glow plug at 0.5–2.0 ohms and confirm 10–25 amp draw per circuit during the preheat cycle.

Overview: All Brands SPN 1267 FMI 3

Glow plugs heat the combustion chamber for cold starts on diesel engines. A circuit fault that sets SPN 1267 FMI 3 disables preheat, and the engine cranks normally but never fires when ambient temp drops below freezing. The fix is usually one bad plug or a chafed harness — not a fuel system problem.

Repair Snapshot

Time

1 - 3 Hours

Difficulty

Intermediate

Parts Cost

$30 - $400

Dealer Labor

$250+

Tools Required

  • Cummins INSITE
  • Snap-on NEXIQ
  • Multimeter
  • Test Light

What SPN 1267 FMI 3 Means

SPN 1267 FMI 3 flags a glow plug circuit voltage fault that prevents proper preheat in cold weather, causing hard no-starts below 32°F. Glow plugs should draw 10–25 amps each during preheat with supply voltage at 11.5–12.6 V. Test each plug at 0.5–2.0 ohms and verify module output before replacing the entire harness.

Symptoms Drivers Notice

  • SPN 1267 FMI 3 or companion glow plug circuit codes
  • Hard crank no-start below 32°F with normal fuel pressure
  • Glow plug indicator lamp off or flashing during preheat cycle
  • White smoke on start attempt without sustained idle
  • Cranking speed normal at 150–250 RPM but no combustion

Most Likely Root Causes

Failed glow plug with open or shorted element

Common

Burned element reads open circuit or shorts to ground, pulling down the entire bank preheat.

Chafed harness shorted to 12 V near exhaust

Common

Heat and vibration damage insulation, setting FMI 3 voltage-above-normal on the circuit.

Failed glow plug control module or relay

Occasional

Module output driver burns out — no current reaches plugs despite good supply voltage at 12 V.

Common Misdiagnoses (Don't Waste Parts)

Replacing the fuel filter on a cold no-start

Why it happens: Hard start is assumed to be fuel related.

Do this instead: Confirm fuel rail pressure at 4,000–5,000 PSI cranking first — normal pressure with no-start below 32°F points at glow plugs.

Replacing only one glow plug without testing the bank

Why it happens: First open plug found gets replaced.

Do this instead: Ohm every plug in the bank — multiple weak plugs are common above 200,000 miles.

Ignoring weak batteries during glow plug diagnosis

Why it happens: Focus stays on the glow plug circuit alone.

Do this instead: Batteries below 11.0 V under load cannot drive 10–25 amps per plug — load-test batteries first.

Master Tech Commentary

Mechanic's Notes

One shorted glow plug on a series-parallel bank can kill preheat for the whole side. Always ohm each plug before swapping the control module. Below 0°F, even good plugs need 2–3 preheat cycles — confirm ambient temp sensor reads correctly.

Step-by-Step Diagnostic Procedure

  1. Step 1: Read glow plug codes in Cummins INSITE or Snap-on NEXIQ — note which cylinder circuit flags SPN 1267 FMI 3.
  2. Step 2: Key on, engine off — measure glow plug relay or module supply at 11.5–12.6 V; below 11.0 V indicates battery or cable fault, not glow plug.
  3. Step 3: During commanded preheat, measure current draw per glow plug circuit — each plug should pull 10–25 amps for 30–120 seconds depending on ambient temp.
  4. Step 4: Disconnect each glow plug and measure resistance to ground — spec is typically 0.5–2.0 ohms; open circuit or under 0.3 ohms means failed plug.
  5. Step 5: Inspect glow plug harness for chafing near exhaust manifold — short to 12 V sets FMI 3; repair harness before replacing the module.

Live Data & Freeze-Frame Tips

In INSITE or NEXIQ, monitor glow plug commanded state, preheat duration, intake air temp, and battery voltage during key-on preheat. Commanded ON with zero amp draw means open circuit. Amp draw with no temp rise at intake suggests failed module timing.

Safety Warnings

  • Glow plug tips exceed 1,800°F during operation — do not touch within 10 minutes of shutdown.
  • Disconnect batteries before removing glow plugs to prevent short circuits.
  • Use insulated tools — glow plug terminals sit close to grounded engine block.

When to Limp In vs Tow

Tow if the truck is stranded in sub-zero conditions and glow plug repair cannot be completed on-site, especially with loaded freight and no block heater available.

Prevention Tips for Fleets & Owner-Operators

  • Replace glow plugs as a set above 150,000 miles or at first cold-start complaint.
  • Keep batteries load-tested — maintain above 12.4 V resting, 11.5 V minimum during preheat.
  • Route harness away from exhaust heat shields during any engine work.
  • Use block heater below 20°F to reduce glow plug duty cycle and extend plug life.

Related Fault Codes

SPN 1268 FMI 4

Glow plug circuit voltage below normal — companion to FMI 3 on adjacent cylinder.

SPN 102 FMI 18 — Boost Pressure

Intake manifold temperature — confirms ambient cold enough to require preheat.

SPN 157 FMI 1 — Injector Metering Rail 1 Pressure

Fuel rail pressure low — rule out before condemning glow system.

Frequently Asked Questions

What code indicates a glow plug circuit fault?

SPN 1267 FMI 3 signals voltage above normal or short to high source on glow plug circuit 1. Similar SPN 1268–1277 cover additional cylinders.

What ohm reading should a glow plug have?

Most heavy-duty glow plugs measure 0.5–2.0 ohms at 68°F. Open circuit or below 0.3 ohms indicates replacement.

How many amps should glow plugs draw?

Each plug typically draws 10–25 amps during the preheat cycle. Zero amps with commanded ON means open circuit or failed module.

Will a diesel start without glow plugs above freezing?

Most heavy-duty engines start above 50°F without preheat. Below 32°F, failed glow plugs cause hard no-start or long crank times.

Can one bad glow plug prevent starting?

On series-wired banks, one shorted or open plug can disable preheat for multiple cylinders — test the entire bank, not just the flagged circuit.

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