Cummins fault code 266
Engine Fuel Temperature: reading above normal (most severe)
What it means
Cummins' description: Engine Fuel Temperature - Data valid but above normal operational range - Most Severe Level.
SPN 174 is Engine Fuel Temperature 1. FMI 0 means the sensor is working, but the value it reports is far above where it should be. This is the most severe 'high' level.
The low-pressure side supplies fuel from the tank to the high-pressure pump. It includes the lift pump, fuel filters, water separator, fuel temperature sensor and water-in-fuel sensor.
What the lamp means
A red stop lamp means Cummins treats this as serious. Stop the engine as soon as you can do it safely and get it checked before running it again.
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. Cummins rates this a red stop lamp code, so if the red lamp is on, go by the red example.
Keep an eye on it
A water-in-fuel light that clears after draining the separator, with the engine running normally.
Schedule a repair
Codes return after draining, or power loss under load. Replace filters and have the supply side tested.
Stop and get help
Repeated water in fuel, stalling, or no-start. Stop running it. Water in a common rail system can quickly ruin injectors and the high-pressure pump.
Common causes
The sensor reading itself is out of range or the condition is real, so look at the system:
- Water in the fuel or a full water separator bowl
- Clogged fuel filter
- Weak or failed lift pump
- Restricted or pinched fuel line
- Low fuel, or fuel gelling in cold weather
What you can check before calling
- Drain the water separator and see if water comes out
- Check when the fuel filters were last changed
- Make sure the tank isn't low, especially on a slope
- In cold weather, think about fuel gelling
Clearing the code without fixing the cause usually brings it right back, and on emissions systems it can restart derate timers.
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: Cummins Tier 4 Fault Codes. Always confirm with Cummins service information (QuickServe) for your engine serial number.
Same SPN, other failure types
- 261 SPN 174 FMI 16
Engine Fuel Temperature: reading above normal (moderately severe) - 263 SPN 174 FMI 3
Engine Fuel Temperature Sensor 1 Circuit: circuit voltage high / shorted high - 264 SPN 174 FMI 11
Fuel Temperature Sensor Circuit: root cause not known - 265 SPN 174 FMI 4
Engine Fuel Temperature Sensor 1 Circuit: circuit voltage low / shorted low - 535 SPN 174 FMI 2
Engine Fuel Temperature: erratic or intermittent signal
Related Fuel supply and water in fuel codes
- 418 SPN 97 FMI 15
Water in Fuel Indicator: reading above normal (least severe) - 428 SPN 97 FMI 3
Water in Fuel Indicator Sensor Circuit: circuit voltage high / shorted high - 429 SPN 97 FMI 4
Water in Fuel Indicator Sensor Circuit: circuit voltage low / shorted low - 546 SPN 94 FMI 3
Fuel Delivery Pressure Sensor Circuit: circuit voltage high / shorted high - 547 SPN 94 FMI 4
Fuel Delivery Pressure Sensor Circuit: circuit voltage low / shorted low - 1852 SPN 97 FMI 16
Water in Fuel Indicator: reading above normal (moderately severe)
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 266 mean?
Cummins fault code 266 is J1939 SPN 174 FMI 0: Engine Fuel Temperature - Data valid but above normal operational range - Most Severe Level. In plain terms: engine fuel temperature: reading above normal (most severe).
Can I keep driving with Cummins code 266?
No. Cummins assigns this code a red stop lamp. Stop the engine as soon as it's safe and have it checked before running it again. Look at the green, yellow and red examples on this page to judge your situation.
What is the SPN and FMI for Cummins code 266?
SPN 174 identifies the part or system (Engine Fuel Temperature 1). FMI 0 describes the type of failure: reading above normal (most severe).
What usually causes Cummins code 266?
The most common causes are: water in the fuel or a full water separator bowl; clogged fuel filter; weak or failed lift pump.
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.