Detroit Diesel · Injector Solenoid Driver Circuit - Cylinder #2High

Detroit Diesel SPN 652 FMI 6: Injector Cylinder #2 Shorted Circuit

SPN 652 FMI 6 (FMI 6) — Engine Injector Cylinder #2 - Current Above Normal or Grounded Circuit

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Quick Answer

SPN 652 FMI 6 means the cylinder #2 injector driver circuit on a Detroit Diesel engine is shorted to ground or drawing excessive current. It is High severity, does not shut the engine down, but should be repaired quickly to avoid damaging the ECM injector driver stage.

Overview: Detroit Diesel SPN 652 FMI 6

Detroit Diesel DD13, DD15, and DD16 engines use individual injector cylinder codes just like Cummins, with SPN 652 covering cylinder #2 specifically. The FMI 6 designation means current above normal, which is the electrical opposite of an open circuit - this is a short, not a break. As ProfessionalDieselRepair.com explains to shops handling these engines, a shorted injector circuit deserves faster attention than an open one because repeated key cycles with an active short can overheat and damage the injector driver transistor built into the ECM, turning a simple harness repair into an expensive control module replacement.

Repair Snapshot

Time

2 - 4 Hours

Difficulty

Advanced

Parts Cost

$60 - $700

Dealer Labor

$650+

Tools Required

  • Detroit Diesel Diagnostic Link (DDDL)
  • Multimeter
  • Snap-on NEXIQ USB Link
  • Valve Cover Gasket

What SPN 652 FMI 6 Means

SPN 652 FMI 6 means the Detroit Diesel ECM has detected excessive current or a short to ground in the cylinder #2 injector driver circuit. Unlike an open circuit, a shorted driver can potentially damage the injector driver stage inside the ECM if left unaddressed. The MIL illuminates immediately and the engine will run rough on the affected cylinder, though it will not typically shut down.

Symptoms Drivers Notice

  • Rough idle with a noticeable miss traceable to cylinder #2
  • Amber MIL illuminated
  • Possible burnt smell or visible damage near the injector connector
  • Reduced power and fuel economy

Most Likely Root Causes

Chafed injector harness shorting to the cylinder head or valve cover

Common

The tight routing of the valve cover harness against metal surfaces on DD platforms makes this the single most frequent cause of a shorted injector circuit.

Water intrusion at the injector connector

Common

A failed connector seal lets coolant or wash water into the injector plug, creating a conductive path to ground.

Internally shorted injector solenoid

Occasional

Heat and vibration fatigue can break down the internal winding insulation of the solenoid, shorting it to the injector body.

Damaged ECM injector driver stage

Rare

If the short has been present for an extended period, the ECM's own driver circuit for that cylinder can be damaged and require ECM replacement or repair.

Common Misdiagnoses (Don't Waste Parts)

Replacing the injector before checking for a shorted harness

Why it happens: This is a textbook parts-cannon move - swapping the injector without ever ohming the harness to ground first, sometimes leading to the new injector failing again within days.

Do this instead: Always check the harness to ground independently of the injector before condemning either part, since a shorted harness will damage a brand new injector just as fast as the old one.

Ignoring a burnt smell as unrelated

Why it happens: Techs assume a burnt electrical smell is coming from somewhere else on the engine.

Do this instead: Trace any burnt smell directly to the injector connectors first, since a hard short can visibly melt connector plastic.

Not checking for ECM driver damage after the repair

Why it happens: Once the harness or injector is fixed, techs assume the fault is fully resolved.

Do this instead: Verify injector balance rates in DDDL after any repair to confirm the ECM driver circuit for that cylinder wasn't damaged by the prolonged short.

Master Tech Commentary

Mechanic's Notes

Shop tip: a shorted injector circuit is more urgent than an open one because it can cook the driver transistor inside the ECM if the truck keeps getting restarted and driven with the fault active. ProfessionalDieselRepair.com recommends checking injector balance rates on all cylinders with DDDL after any repair on this code, since a stressed ECM driver stage can show up as a weak balance rate on the affected cylinder even after the wiring is fixed.

Step-by-Step Diagnostic Procedure

  1. Step 1: Connect Detroit Diesel Diagnostic Link (DDDL) and confirm SPN 652 FMI 6 is active, then check for any accompanying injector or harness fault codes.
  2. Step 2: Shut down and unplug the cylinder #2 injector connector, inspecting for melted plastic, burnt pins, or visible arcing which would confirm a hard short.
  3. Step 3: Measure resistance from each injector terminal to chassis ground with a multimeter - any reading other than infinite (OL) confirms a short to ground either in the injector or the harness.
  4. Step 4: If the injector itself reads shorted internally, replace it; if it reads clean, trace the harness from the connector back toward the ECM for a chafe point against the valve cover or head.
  5. Step 5: After repair, clear codes with DDDL and verify no injector driver damage occurred by checking injector balance rates in live data before returning to service.

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

Live Data & Freeze-Frame Tips

In DDDL, pull up the injector balance rate or fuel trim data for all cylinders and compare cylinder #2 against the others - a significant deviation after a repair can indicate lingering ECM driver damage even if the fault code has cleared. Also check freeze-frame data for how long the fault was active before it was noticed, which helps gauge the risk of driver stage damage.

Safety Warnings

  • Disconnect batteries before working on any injector circuit suspected of being shorted to avoid arcing.
  • Allow the engine to cool fully before accessing valve cover components.
  • Inspect for melted or burnt connector plastic before handling with bare hands.
  • Wear eye protection when using a wire brush or contact cleaner near connectors.

When to Limp In vs Tow

Towing isn't usually required immediately, but continuing to run the truck with an active hard short risks ECM driver damage. If a mobile repair or same-day shop visit isn't possible, it's safer to limit driving and get it into a bay quickly rather than accumulate hours on the fault.

Prevention Tips for Fleets & Owner-Operators

  • Inspect valve cover harnesses for chafing at every PM, particularly on high-mileage DD13/DD15 engines.
  • Replace connector seals any time an injector connector is disturbed for service.
  • Route harnesses with fresh clips and ties after any valve cover removal.
  • Address minor rough-idle complaints early before a chafe point develops into a full short.

Related Fault Codes

SPN 652 FMI 5

Same cylinder #2 injector circuit but current below normal (open circuit) instead of shorted.

SPN 651 FMI 6

Same fault type but for the adjacent cylinder #1 injector circuit.

SPN 629 FMI 12

Controller #1 (ECM) bad intelligent device fault, worth checking if driver damage is suspected.

Frequently Asked Questions

Can I drive with SPN 652 FMI 6 active?

The truck will still drive with a rough idle and reduced power, but continuing to operate it with an active hard short risks damaging the ECM's injector driver circuit, so prompt repair is strongly recommended.

How do I reset SPN 652 FMI 6 without a scanner?

A battery disconnect may clear the stored fault temporarily, but it will return on the next key cycle if the short to ground hasn't been physically repaired.

What triggers a derate on this code?

This code alone typically doesn't trigger the multi-mph emissions inducement derate, but the loss of one cylinder reduces available power noticeably under load.

Can this code damage my ECM?

Yes, an unresolved short to ground can overheat the ECM's internal injector driver circuit for that cylinder if the truck is repeatedly started and driven with the fault active.

How do I tell if it's the injector or the harness?

Unplug the injector connector and measure resistance from each terminal to ground independently of the harness - if the injector is disconnected and the short disappears, the injector itself is the problem, not the wiring.

Is FMI 6 more serious than FMI 5 on this SPN?

In practical terms, yes - FMI 6 (shorted/current above normal) carries more risk of ECM driver damage than FMI 5 (open circuit), which simply disables the cylinder without generating excess current.