Cummins fault code 951
Cylinder Power Imbalance between cylinders: erratic or intermittent signal
What it means
Cummins' description: Cylinder Power Imbalance between cylinders.
SPN 166 is Cylinder Power Imbalance between cylinders. FMI 2 means the signal is jumping around, dropping in and out, or doesn't make sense compared to other readings.
The ECM needs clean, steady battery voltage, and it supplies regulated 5-volt power to many sensors. Voltage problems can cause strange codes across many systems at once.
What the lamp means
This code normally doesn't turn on a dash lamp. It's logged in the ECM for a technician to see, and often explains another active code.
Green, yellow, red: three ways this can look
The same code can be a quick fix or a reason to shut down. Match your situation to the closest example.
Keep an eye on it
A low-voltage code after a hard winter start or after the truck sat a while, then clears.
Schedule a repair
Codes return, the truck is slow to crank, or voltage reads low while driving. Test the charging system soon.
Stop and get help
Engine dies, several systems drop out at once, or the ECM loses power. Don't run it until the power supply is fixed. It can leave you stranded.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Weak batteries
- Failing alternator
- Parasitic drain
What you can check before calling
- Check battery terminals and ground straps for corrosion or looseness
- Have the batteries and alternator tested
- Note if several unrelated codes appeared at the same time
Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers. For the bigger picture, read our guide: Bad alternator or bad battery? How to tell.
Engines and sources
Cummins uses the same fault code numbers across its electronic engines, including on-highway models like the ISB/B6.7, ISL/L9 and ISX/X15, though not every code applies to every engine or software level. Source: Diagnostic Fault Codes for Cummins Engines. Always confirm with Cummins service information (QuickServe) for your engine serial number.
Related Battery, power supply and sensor supply codes
- 1117 SPN 3597 FMI 2
Power Supply Lost With Ignition On: erratic or intermittent signal - 718 SPN 1151 FMI 0
High #8 RB Cylinder Power: reading above normal (most severe) - 717 SPN 1150 FMI 0
High #7 RB Cylinder Power: reading above normal (most severe) - 716 SPN 1148 FMI (45)
High #6 RB Cylinder Power: fault - 715 SPN 1147 FMI (45)
High #5 RB Cylinder Power: fault - 714 SPN 1146 FMI (45)
High #4 RB Cylinder Power: fault
Look up another code
Cummins fault code (like 1922), J1939 SPN and FMI (like SPN 3251 FMI 0), or an OBD-II code (like P0420).
Questions
What does Cummins fault code 951 mean?
Cummins fault code 951 is J1939 SPN 166 FMI 2: Cylinder Power Imbalance between cylinders. In plain terms: cylinder power imbalance between cylinders: erratic or intermittent signal.
Can I keep driving with Cummins code 951?
Usually, yes. This code doesn't normally turn on a lamp by itself, but check for other active codes that might be more serious. Look at the green, yellow and red examples on this page to judge your situation.
What is the SPN and FMI for Cummins code 951?
SPN 166 identifies the part or system (Cylinder Power Imbalance between cylinders). FMI 2 describes the type of failure: erratic or intermittent signal.
What usually causes Cummins code 951?
The most common causes are: weak batteries; failing alternator; parasitic drain.
Diesel down in the Midlands?
We work on Cummins-powered pickups, vans and medium-duty trucks across Lexington, Columbia and the Midlands, on site at your yard or roadside.