How to Read a CAT Fuel Injector Part Number: Complete Decoder Guide

Ordering the wrong fuel injector because of a misread part number is one of the most expensive mistakes in diesel engine maintenance. CAT injector part numbers follow specific numbering conventions that, once understood, make identification straightforward. This guide decodes CAT fuel injector part numbering for the most common CAT engine families, including 3406, C7, C10, C12, C15, C18, and 3500 series engines.

1. Understanding CAT Part Number Formats

Caterpillar uses several part number formats depending on the era and component type. Knowing which format applies to your injector is the first step in correct identification:

Table 1: CAT Part Number Formats

Format	Example	Era	Common Use	Where to Find
X-NNNN (Number-Number)	223-5327, 194-5083	1990s-2010s	Most common CAT injector format; used across engine families	Stamped on injector body, solenoid cap, or original packaging
XX-NNNN (Number-Letter dash Number)	10R-1256, 20R-0851	1990s-present	Remanufactured (Reman) components; R indicates remanufactured	Reman packaging; reman injectors have an R prefix
OR-NNNN (Letter-Number)	OR-3420, OR-6219	1980s-2000s	O-ring and seal kits; injector installation hardware	Not the injector itself; these are seal kit part numbers
NNNN-NNN (Eight-digit)	211-3025, 127-8216	1990s-2000s	Fuel injection pump components; plunger and barrel assemblies	Stamped on plunger body or pump housing

2. CAT Injector Part Numbers by Engine Family

Table 2: Common CAT Injector Part Numbers

Engine Family	Injector Type	Common OEM Part Numbers	Key Identification Features
3406E (5EK, 6TS prefix)	HEUI	223-5327, 189-9241, 194-5083	4-digit trim code stamped on solenoid; rectangular electrical connector
C15 (6NZ, MBN, BXS prefix)	HEUI	239-4907, 224-2743, 116-8899	Similar to 3406E; verify trim code compatibility with CAT ET
C15 ACERT (SDP, MXS prefix)	MEUI	10R-1256, 20R-0851, 253-0618	No trim code; calibration file required; different hold-down design
C7 (C7S, KAL, SAP prefix)	HEUI	116-5414, 116-5425, 189-2718	Smaller injector body than 3406E/C15; unique connector orientation
C10/C12 (CPD, MBL, 2PN prefix)	HEUI	116-8899, 189-2718, 223-5327	Some interchangeability with 3406E; always verify with serial number
3406B/C Mechanical (4MG, 5KJ prefix)	Mechanical (pump-line-nozzle)	7W-7038, 7W-7039 (nozzle); 4P-9827, 1W-6539 (plunger)	No electronic components; identified by nozzle tip style and pop pressure
3304/3306 (PC, 8N prefix)	Mechanical pre-combustion chamber	7N-1185, 6N-7527, 7N-5301	Distinctive glow plug location; pre-combustion chamber injector design

3. The Engine Serial Number: The Ultimate Compatibility Key

A CAT part number alone does not guarantee compatibility. The same injector part number may have different calibrations for different engine serial number prefixes. Always verify compatibility using your engine’s serial number prefix (the three-character code before the numeric sequence on the engine data plate).

For example, a 223-5327 injector fits a 3406E engine with a 5EK serial prefix but may require a different trim code or calibration for a 6TS prefix engine. CAT ET (Electronic Technician) software is the authoritative tool for verifying injector compatibility by serial number.

4. Reman vs. New: Understanding CAT Remanufactured Injector Part Numbers

CAT Reman injectors carry an R prefix in their part numbers (e.g., 10R-1256 for a remanufactured injector vs. a new equivalent). Key differences:

• 10R- and 20R- prefix: CAT Remanufactured components. These are genuine CAT injectors rebuilt to OEM specifications at CAT remanufacturing facilities. They carry the same warranty as new CAT parts and include updated design improvements.
• 0R- prefix: CAT Reman with a core charge. You must return the old injector or pay an additional core charge.
• Non-R numbers (e.g., 223-5327): New OEM injectors. These are factory-new and carry the full CAT new parts warranty.

CAT Reman injectors are an excellent value for many applications. They have been completely disassembled, inspected, had all wear components replaced, and been tested to meet the same performance specifications as new injectors. The remanufacturing process also incorporates any design updates or improvements made since the injector was originally manufactured.

5. Avoiding Common Part Number Mistakes

Table 3: Common Part Number Errors and How to Avoid Them

Error	Consequence	How to Avoid
Confusing injector part number with seal kit part number	Ordering O-rings instead of the complete injector	CAT seal kits start with OR-; injectors start with a number
Missed digit in the part number (e.g., 194-508 vs. 194-5083)	Wrong injector delivered; may or may not physically fit	Always verify the full part number from the injector body, not from memory or unverified notes
Assuming same part number means same calibration	Correct injector, wrong trim code or calibration for your specific engine serial prefix	Always cross-reference with engine serial number using CAT ET or the CAT parts system
Ordering by engine model without serial number	C15 engines built in different years have different injectors; C15 Bridge (pre-ACERT) vs. C15 ACERT are completely different	Engine serial number prefix (first 3 characters) is mandatory for accurate injector identification
Mixing 3406E and C15 injectors without verification	Some interchange, some do not; depends on serial prefix and production year	Treat all cross-family interchanges as requiring explicit verification

6. Aftermarket Injector Part Number Cross-Referencing

Quality aftermarket injector suppliers provide cross-reference information mapping OEM CAT part numbers to their equivalent products. When buying aftermarket injectors:

• The aftermarket part should explicitly cross-reference to your specific CAT OEM part number
• The supplier should provide trim code or calibration data compatible with your specific engine serial prefix
• For remanufactured aftermarket injectors, verify that all wear components (nozzle, plunger, control valve, seals) have been replaced, not just cleaned
• Request a test report showing balance rates, return flow, and flow matching data at multiple test points

A reputable aftermarket supplier will ask for your engine serial number or at minimum your engine serial prefix before recommending an injector. Suppliers who sell by engine model alone without requesting the serial number should be approached with caution—they may be selling a one-size-fits-all injector that fits multiple applications but is not calibrated correctly for any of them.

Conclusion

CAT fuel injector part numbers follow logical conventions that make correct identification straightforward once you understand the system. The three-part formula for ordering the right injector every time: correct OEM part number + correct engine serial number prefix + verification of trim code or calibration compatibility. Following this formula eliminates the most common—and most expensive—injector ordering mistakes.

Browse our complete CAT fuel injector catalog organized by part number and engine family. Every injector listing includes OEM part number cross-references and engine serial prefix compatibility information. Need help identifying your injector? Contact us with your engine serial number and we will verify compatibility before you order.