Scania · Injector Cylinder #2High

Scania SPN 652 FMI 5: Diagnosing an Open Cylinder #2 Injector Circuit

SPN 652 FMI 5 (FMI 5) — Engine Injector Cylinder #02 - Current Below Normal Or Open Circuit

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Quick Answer

SPN 652 FMI 5 on Scania engines means cylinder #2's injector circuit is reading current below normal, consistent with an open circuit. It's a high-severity fault causing a real misfire on that cylinder, often traced to a connector issue rather than a failed injector.

Overview: Scania SPN 652 FMI 5

An open injector circuit takes a cylinder completely out of the firing sequence, and on Scania engines SPN 652 pinpoints that failure directly to cylinder #2. ProfessionalDieselRepair.com approaches this fault the same way as any single-cylinder injector code - verify the connector and harness integrity before condemning the injector itself, since a corroded pin produces an identical open-circuit reading without any actual injector failure.

Repair Snapshot

Time

1.5 - 4 Hours

Difficulty

Advanced

Parts Cost

$160 - $850

Dealer Labor

$600+

Tools Required

  • Scania SDP3
  • Texa Diagnostic Tool
  • Diesel Laptops Scan Tool
  • Injector Torque Wrench

What SPN 652 FMI 5 Means

SPN 652 FMI 5 means the ECM commanded cylinder #2's injector but measured current below normal, consistent with an open circuit. On a Scania engine this is a high-severity fault - that cylinder is effectively not firing, causing a noticeable miss and reduced power until the open circuit is located and repaired.

Symptoms Drivers Notice

  • Rough idle with a distinct, feelable miss
  • Reduced power and torque, especially under load
  • Check Engine lamp illuminated
  • Increased fuel consumption from the ECM compensating on remaining cylinders

Most Likely Root Causes

Corroded or backed-out harness connector pin

Common

A pin that isn't making solid contact at the injector connector reads as an open circuit even though the injector itself may be perfectly healthy.

Broken wire within the injector harness

Occasional

Repeated flexing at a harness routing point can eventually fracture a wire internally, creating an open circuit without visible external damage.

Failed injector solenoid winding

Occasional

The injector's internal coil can fail open after extended service life, requiring injector replacement rather than a wiring repair.

ECM driver circuit fault for that cylinder

Rare

An internal ECM issue isolated to one injector driver circuit is uncommon but worth considering if harness and injector both test normal.

Common Misdiagnoses (Don't Waste Parts)

Replacing the injector before checking the connector

Why it happens: The fault points directly at the injector circuit, making the injector an easy first parts-cannon target.

Do this instead: Clean and inspect the connector pins first, and check resistance with the injector both connected and disconnected to isolate the actual fault location.

Master Tech Commentary

Mechanic's Notes

Shop tip: check the connector pins before you pull the injector. ProfessionalDieselRepair.com regularly finds a corroded or slightly backed-out harness pin causing this exact fault - a five-minute connector cleaning can save an unnecessary injector replacement.

Step-by-Step Diagnostic Procedure

  1. Step 1: Pull the fault with Scania SDP3 and confirm SPN 652 FMI 5 is active; check whether any adjacent cylinder codes are present, which could point to a shared harness section rather than an isolated connector issue.
  2. Step 2: Locate the cylinder #2 injector connector and inspect it for corrosion, a bent or backed-out pin, or a connector that isn't fully seated.
  3. Step 3: Disconnect the connector and measure resistance across the injector solenoid winding, comparing to spec and to a known-good cylinder on the same engine.
  4. Step 4: If resistance reads open, trace the harness from the connector back toward the ECM, checking for a break at any point where it flexes or routes near a hot component.
  5. Step 5: If the injector itself tests open internally at its own terminals, replace the injector following Scania's proper procedure, including any required calibration data entry.
  6. Step 6: Clear the code and use SDP3's cylinder contribution test to confirm cylinder #2 is now firing evenly with the rest before returning the truck to service.

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

Live Data & Freeze-Frame Tips

Use SDP3's cylinder contribution test to confirm cylinder #2 is producing little or no power relative to the others, corroborating the fault code with a real performance measurement. Compare injector resistance across all cylinders side by side to quickly spot the outlier reading open on #2.

Safety Warnings

  • Disconnect the battery before disconnecting any injector harness connector.
  • Allow the engine to cool before working around injector connectors near the valve cover.
  • Follow correct torque specifications when reinstalling any injector to prevent fuel leaks.

When to Limp In vs Tow

Towing generally isn't necessary for a single dead cylinder, but if power loss is severe enough to be unsafe in traffic, arrange service before continuing to drive.

Prevention Tips for Fleets & Owner-Operators

  • Inspect injector connectors for corrosion during valve cover service intervals.
  • Keep connector seals in good condition to prevent moisture intrusion.
  • Address any intermittent injector faults promptly before they progress to a full open circuit.

Related Fault Codes

SPN 652 FMI 6

Same cylinder #2 injector circuit flagged as current above normal (shorted) instead of open - a different electrical failure mode.

SPN 651 FMI 6

Cylinder #1 injector circuit shorted to ground - a different cylinder and failure mode, useful to check if a broader harness issue is suspected.

Frequently Asked Questions

Can I drive with SPN 652 FMI 5 active?

You can drive short distances, but expect rough idle, reduced power, and poor fuel economy. Get it repaired promptly rather than running long-term on fewer cylinders.

How do I reset SPN 652 FMI 5 without a scan tool?

You need SDP3 or a Texa-compatible scan tool to clear the stored fault after the connector, harness, or injector issue is repaired.

Does this code mean I need a new injector?

Not necessarily - check the connector and harness for corrosion or damage first, since these cause this exact fault more often than a genuinely failed injector.

Will this cause an engine derate?

A dead cylinder reduces overall available power, and depending on the severity and duration, the ECM's protection strategy may apply additional limitations.

How can I tell if it's the injector or the wiring?

Check resistance directly at the injector's own terminals versus at the harness connector - if the injector itself reads normal but the harness end reads open, the wiring is at fault.

Is it safe to keep driving with one dead cylinder for a while?

It's not immediately dangerous, but unburned fuel entering that cylinder over an extended period can eventually affect oil dilution and exhaust system components, so repair it sooner rather than later.