Detroit SPN723FMI8 Fault Code: This Code Sets When the Camshaft Position (CMP) Sensor Signal Has Timed Out for an Extended Period of Time
Also called Camshaft Position Sensor Time Out, SPN 723/FMI 8, This Fault Code Sets When the Motor Control Module (MCM) Does Not Receive a Signal from the Camshaft Position Sensor, This Fault Code Sets When the Motor Control Module (MCM) Does Not Receive a Signal from the Camshaft Position Sensor., This fault code sets ehen the Motor Control Module (MCM) does not receive a signal from the camshaft position sensor, Time Out
This Code Sets When the Camshaft Position (CMP) Sensor Signal Has Timed Out for an Extended Period of Time · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
SPN 723/FMI 8 sets when the Motor Control Module (MCM) does not receive a signal from the Camshaft Position (CMP) sensor for an extended period while the engine is running. Expect the MIL, CEL, and in some cases SEL to light up, along with an engine derate and, on some configurations, a shutdown after 20 seconds.
High severity. This code triggers an engine derate, and on some setups a full shutdown 20 seconds after the fault becomes active. It should be diagnosed the same day it appears, and sooner if the truck is losing power on the road.
What does Detroit error code SPN723FMI8 mean?
SPN 723 FMI 8 means the MCM is not seeing a usable signal from the camshaft position sensor while the engine is running. The CMP sensor tells the ECM where the camshaft is in its rotation, which the engine control system uses for fuel injection timing and cylinder identification. Without that signal, the engine control system cannot safely manage combustion timing.
Because this is a timing-related fault, Detroit engines respond aggressively: the dash shows the Malfunction Indicator Light, Check Engine Light, and on some builds the Service Engine Light. Depending on the specific software calibration, the engine will either derate output by 25% and shut down after 20 seconds, or simply derate without a defined shutdown timer.
The fault is checked continuously while the engine runs (monitor sequence: always), and the typical time for the signal loss to be recognized as a fault is two seconds. Technicians verify a repair by running the engine for one minute (or in some diagnostic revisions, five minutes) and rechecking for the code.
What triggers a Detroit SPN723FMI8 code?
The code sets when the MCM does not receive a signal from the camshaft position sensor while the engine is running, with a typical duration of two seconds of signal loss before the fault sets. Enabling condition is simply the engine running, and the monitor runs continuously (always) with no separate execution frequency limit.
Common causes of SPN723FMI8
- Damaged, corroded, bent, spread, unseated, or broken pins in the CMP sensor connector or the MCM 120-pin connector
- Wire damage or moisture intrusion (seal damage) near the CMP sensor or MCM connectors
- An open or high-resistance CMP signal circuit between the CMP sensor and the MCM (resistance should be less than five ohms between pin 2 of the CMP harness connector and pin 45 of the MCM 120-pin connector)
- A shorted CMP circuit to ground or between CMP signal pins (resistance should read greater than 10K ohms between pin 2 and ground, and greater than 10K ohms between pins 1 and 2, and between pins 2 and 3)
- A failed CMP sensor itself, found on removal and inspection
- Damage to the camshaft tone wheel or excessive gear train lash, especially after gear train, camshaft, or flywheel repair work
- On some engine builds before February 2019, an older 'ribbed' design fuel injector harness with pin damage or corrosion at pins 13, 14, or 15 of the 16-pin injector harness connector, which can affect the CMP signal, ground, or VREF circuits routed through that harness
How to troubleshoot Detroit SPN723FMI8: first checks
- Confirm cranking speed is over 150 rpm using DiagnosticLink Standard before doing further diagnosis
- Turn the ignition off, disconnect the CMP sensor harness connector, and inspect both the sensor and connector for bent, spread, broken, unseated, or corroded pins, moisture, or wire damage
- With the ignition on (key on, engine off), measure voltage between pins 1 and 3 on the harness side of the CMP sensor, and separately between pin 1 and battery ground; both should read between 4.5 and 5.5 volts
- Disconnect the MCM 120-pin connector and inspect it the same way for damage or corrosion
- Check resistance between pin 2 of the CMP harness connector and pin 45 of the MCM 120-pin connector (should be less than five ohms), and check for shorts to ground or between CMP pins (each should read greater than 10K ohms)
- On engines built before February 2019, inspect the fuel injector wiring harness style and check pins 13, 14, and 15 of the 16-pin injector connector for corrosion, damage, or spread pins, since a resistance between the CMP SIG circuit and ground should read between 200k ohms and 500k ohms, and later checks at the CMP sensor connector itself should read between 220k ohms and 360k ohms
- Remove the CMP sensor and inspect it for physical damage, and inspect the camshaft tone wheel and gear train for damage or excessive lash, particularly if any recent gear train, camshaft, or flywheel repairs were performed
How the code clears
No separate reset procedure is listed for this code beyond correcting the underlying wiring, connector, sensor, or mechanical issue. After repairs, reconnect all harnesses, start the engine, and let it run for one minute (or five minutes on the injector-harness-related diagnostic path) before rechecking with DiagnosticLink to confirm SPN 723/FMI 8 is no longer active.
Frequently asked questions
What does Detroit SPN 723 FMI 8 mean?
It means the Motor Control Module did not receive a signal from the camshaft position sensor while the engine was running, and the signal was missing long enough (around two seconds) for the fault to set.
Will SPN 723 FMI 8 shut my engine down?
It can. On some configurations the engine derates output by 25% and shuts down 20 seconds after the fault becomes active. Other calibrations apply a derate without a defined shutdown timer. Either way, treat it as a stop-soon condition.
What voltage should the camshaft position sensor read?
With the ignition on and engine off, voltage between pins 1 and 3 on the harness side of the CMP sensor, and between pin 1 and battery ground, should each read between 4.5 and 5.5 volts. Voltage outside that range points to a wiring or power supply problem rather than the sensor itself.
Can a bad injector harness cause this code?
Yes, on engines built before February 2019, the older 'ribbed' design fuel injector harness can develop corrosion or pin damage at pins 13, 14, or 15 of the 16-pin connector, which can affect CMP signal, ground, or reference voltage circuits and trigger this code.
How do I know if it's the sensor or the wiring harness?
Check connector pins for damage and corrosion first, then verify voltage and resistance values at the CMP sensor and MCM connectors. If wiring and connectors check out within spec, remove the CMP sensor and inspect it directly, and also check the camshaft tone wheel and gear train for damage.
Does a recent camshaft or flywheel repair matter for this code?
Yes. If the engine has had gear train, camshaft, or flywheel repair work done, that is a specific point to check, since it can affect tone wheel alignment or condition and cause a lost camshaft position signal.
How do I confirm the repair fixed the code?
After repairs, start the engine and let it run for one minute (or five minutes depending on the diagnostic path used), then check with DiagnosticLink to make sure SPN 723/FMI 8 is no longer active.