Kenworth · Injector Cylinder 2High

Kenworth SPN 652 FMI 6: Injector Cylinder 2 Current Below Normal

SPN 652 FMI 6 (FMI 6) — Injector Cylinder 2 - Current Below Normal

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Quick Answer

SPN 652 FMI 6 means the ECM measured below-normal actuator current on cylinder 2 injector circuit. Misfire, rough idle, and possible injector shutdown derate can follow until resistance and wiring are verified against OEM specs.

Overview: Kenworth SPN 652 FMI 6

Cylinder-specific injector current faults are common on PACCAR and Cummins-powered Kenworth trucks, and ProfessionalDieselRepair.com isolates harness versus injector failures with swap tests before recommending a full set replacement.

Repair Snapshot

Time

2 - 5 Hours

Difficulty

Advanced

Parts Cost

$350 - $900

Dealer Labor

$750+

Tools Required

  • Noregon JPRO
  • Cummins INSITE
  • Digital Multimeter
  • Injector Puller Set

What SPN 652 FMI 6 Means

Kenworth SPN 652 FMI 6 reports cylinder 2 injector actuator current below normal on common-rail engines, indicating weak solenoid drive or high resistance in the circuit. Expect rough idle, cylinder misfire, white smoke, and a progressive multi-cylinder derate if the ECM disables the affected injector.

Symptoms Drivers Notice

  • Rough idle and cylinder 2 misfire logged in Noregon JPRO or OEM tool
  • White or gray smoke at idle that clears at higher RPM
  • Engine vibration noticeable at low speed in gear
  • Fuel trim or balance rates show cylinder 2 contributing low
  • Fault may appear after harness repair near valve cover

Most Likely Root Causes

Failed cylinder 2 injector solenoid coil

Common

High internal resistance drops current below ECM thresholds and weakens injection events.

Valve-cover harness oil intrusion

Common

Oil degrades connector pins and increases circuit resistance at the injector branch.

ECM injector driver degradation

Rare

A weak driver channel on the ECM cannot supply rated current even with a good injector.

Common Misdiagnoses (Don't Waste Parts)

Replacing all injectors when only cylinder 2 faults

Why it happens: Fleets bundle injector jobs to reduce downtime.

Do this instead: Swap test cyl 2 with a known-good bank neighbor; parts-cannon six-packs hide a $40 harness repair.

Assuming low current means low fuel pressure globally

Why it happens: Misfire symptoms mimic rail pressure faults.

Do this instead: Confirm rail pressure spec first — typically 5000+ psi cranking on common-rail — then focus on cylinder 2 circuit.

Master Tech Commentary

Mechanic's Notes

ProfessionalDieselRepair.com swaps harness branches before injectors on Kenworth SPN 652 FMI 6 — low current often traces to oil-fouled valve-cover pigtails, not a dead injector. Replacing all six without isolation is a parts-cannon habit that burns margin.

Step-by-Step Diagnostic Procedure

  1. Step 1: Run cylinder cutout test in JPRO; cylinder 2 change in RPM should be minimal compared to healthy cylinders.
  2. Step 2: Measure injector connector resistance on cylinder 2 — many common-rail solenoids read 0.5-2.0 ohms at 68°F; above 3 ohms indicates failing coil.
  3. Step 3: Backprobe ECM injector driver output during cranking; compare peak current on cyl 2 versus cyl 1 — below 10A peak suggests driver or wiring loss.
  4. Step 4: Inspect valve-cover harness pigtail for oil soak and cracked insulation at the cylinder 2 branch.
  5. Step 5: Swap cylinder 2 injector connector with cylinder 4 temporarily; if the fault follows the connector, repair harness — if it stays on cyl 2, replace injector.

Professional service / OEM-level scan tools are recommended before clearing this fault for good.

Live Data & Freeze-Frame Tips

Use JPRO injector balance rates or equivalent cylinder contribution data at idle. Cylinder 2 should match neighbors within a few percent; a persistent negative outlier with low current confirms FMI 6 focus.

Safety Warnings

  • Relieve high-pressure fuel before removing injectors.
  • Keep dirt out of open fuel galleries during service.
  • Use insulated tools near live injector circuits.

When to Limp In vs Tow

Tow if the engine runs on fewer cylinders, stalls at stops, or sets additional injector shutdown codes that limit speed below safe traffic flow.

Prevention Tips for Fleets & Owner-Operators

  • Replace valve-cover gaskets before oil reaches harness.
  • Torque injector hold-downs to OEM spec during service.
  • Use clean diesel and change filters on interval.

Related Fault Codes

SPN 653 FMI 7 — Injector Cylinder 3

Cylinder 3 injector mechanical not responding — adjacent cylinder fault pattern.

SPN 654 FMI 5 — Injector Solenoid Driver Circuit - Cylinder #4

Cylinder 4 injector open or low current — similar diagnostic path.

Frequently Asked Questions

What is Kenworth SPN 652 FMI 6?

It means ECM measured injector actuator current below normal on cylinder 2, indicating weak electrical drive to that injector.

Can I drive with one cylinder misfiring?

Short distances may be possible but risk catalyst damage, fuel dilution, and further derates; repair promptly.

What ohms should the injector read?

Most common-rail solenoid injectors measure roughly 0.5-2.0 ohms at room temperature; significantly higher indicates failure.

Does swapping injectors help diagnose?

Yes. Moving the injector to another cylinder shows whether the fault follows the injector or stays with the harness.

Will this code clear after repair?

After fixing current to spec, clear codes and verify with cutout test and road idle quality.

Is the ECM ever at fault?

Possible but rare; prove injector and harness first with swap and current comparison tests.

More Kenworth codes on this system

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