Caterpillar · Camshaft Position SensorMedium

Caterpillar SPN 723 FMI 9: Camshaft Sensor Abnormal Update Rate

SPN 723 FMI 9 (FMI 9) — Engine Camshaft Speed/Position Sensor - Abnormal Update Rate

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Quick Answer

SPN 723 FMI 9 means the camshaft position sensor's signal timing is off from what the ECM expects. It's Medium severity - a backup-sensor data quality issue that rarely causes drivability problems but is worth fixing for full redundancy.

Overview: Caterpillar SPN 723 FMI 9

ProfessionalDieselRepair.com typically finds an air gap or connector issue behind this fault rather than a genuinely bad sensor.

Repair Snapshot

Time

1 - 2 Hours

Difficulty

Intermediate

Parts Cost

$120 - $300

Dealer Labor

$400+

Tools Required

  • Cat ET (Electronic Technician)
  • Multimeter
  • Diesel Laptops Diagnostic Software
  • Jaltest

What SPN 723 FMI 9 Means

SPN 723 FMI 9 means the camshaft position sensor signal is updating slower or faster than the ECM expects, rather than dropping out entirely. This is Medium severity - a data-quality issue on a backup sensor that rarely affects drivability but should be addressed to maintain full engine speed signal redundancy.

Symptoms Drivers Notice

  • Amber check engine light with no noticeable drivability change
  • Fault may be intermittent across drive cycles
  • No power loss under normal operating conditions
  • Possible slightly harder cold start in rare cases

Most Likely Root Causes

Incorrect camshaft sensor air gap

Common

Mechanical setup issue - a gap slightly outside spec produces a distorted, irregularly-timed signal rather than a total loss of signal.

Corroded or loose sensor connector

Common

Electrical fault - a marginal connection can distort signal timing without fully breaking the circuit.

Harness chafing near the gear housing

Occasional

Electrical fault - vibration-related wear in this area degrades signal quality over time.

Failing internal sensor electronics

Occasional

Genuine sensor hardware issue confirmed after air gap and connector checks pass clean.

Common Misdiagnoses (Don't Waste Parts)

Replacing the sensor as the first step

Why it happens: It feels like the direct fix for a sensor-named code.

Do this instead: This is a parts-cannon shortcut - check and correct the air gap first, since that alone resolves a large share of these calls without any parts cost.

Escalating this to an urgent repair

Why it happens: Any camshaft-related fault sounds serious to drivers unfamiliar with backup sensor redundancy.

Do this instead: Explain this is a data-quality issue on a backup signal with minimal drivability risk, and schedule it as routine maintenance rather than an emergency.

Master Tech Commentary

Mechanic's Notes

ProfessionalDieselRepair.com tip: check the air gap before the sensor itself - an abnormal update rate is a classic symptom of a slightly incorrect gap setting rather than a truly failed part.

Step-by-Step Diagnostic Procedure

  1. Step 1: Connect Cat ET or Diesel Laptops software and confirm the update rate fault is active, checking how frequently it recurs.
  2. Step 2: Inspect the camshaft position sensor connector at the rear of the cylinder head for corrosion or a loose locking tab.
  3. Step 3: Check the sensor's air gap against Cat specification - an incorrect gap after any timing cover or gear train service can produce this exact abnormal update rate fault.
  4. Step 4: Back-probe the signal circuit with a multimeter or scope to check for a consistent, regularly-timed pulse pattern while cranking.
  5. Step 5: Inspect the harness for chafing or heat damage near the gear housing and exhaust manifold.

Live Data & Freeze-Frame Tips

In Cat ET, review the sensor's pulse timing data if available - an update rate that varies noticeably between cranks or during warm-up points to an air gap or connector issue rather than a fully failed sensor.

Safety Warnings

  • Allow the engine to cool before accessing the camshaft sensor near the cylinder head.
  • Disconnect the battery before removing the sensor to prevent accidental cranking.

When to Limp In vs Tow

Not necessary - this fault has minimal to no drivability impact in the vast majority of cases.

Prevention Tips for Fleets & Owner-Operators

  • Always verify air gap after timing cover or gear train service.
  • Inspect connectors for corrosion during PM service.
  • Address abnormal update rate codes at the next scheduled service rather than letting them persist indefinitely.

Related Fault Codes

SPN 723 FMI 2

Fully erratic/intermittent camshaft signal - a more severe version of a similar sensor timing problem.

SPN 190 FMI 9

Abnormal update rate on the primary crankshaft speed signal - a more serious equivalent fault.

Frequently Asked Questions

Can I keep driving with this code active?

Yes - this backup sensor fault rarely causes drivability issues, though it's worth fixing to maintain full signal redundancy.

How do I reset it without a scanner?

It may clear after a key cycle, but it will return if the air gap or connector issue isn't actually corrected.

Does this trigger a derate?

No, this is not an emissions-related fault and won't trigger a power reduction.

Is this the same as a fully failed cam sensor?

No - this specifically means the signal timing is abnormal, not that the signal is completely missing, which is a slightly different and generally less urgent fault.

How much does this repair cost?

An air gap correction is essentially free in labor. A full sensor replacement with labor typically runs $250-$300.

Why does this fault come and go?

Marginal air gap or connector issues often only produce a detectable timing abnormality under specific temperature or vibration conditions.