Union Pacific SD40N Locomotives

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This page was last updated on January 27, 2021.

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(After 2018, this information is no longer being updated.)


Beginning with the completion of UP 1550 on May 4, 2010, Union Pacific began modifying its refurbished SD40-2 locomotives with an updated and modern control system known as NEXSYS, supplied by ZTR Control Systems. Each locomotive was given a formal completion date, retaining its original SD40-2 model desigation. With the completion of UP 1629 on July 8, 2011, UP began using a new model designation: SD40N, denoting the railroad's "SD40-2 Modernization Program."

The 'N' part of the designation comes from UP's use of the NEXSYS control system from ZTR Control Systems, replacing the older Dash 2 component cards and control systems. (ZTR web site).

UP's SD40-2 Moderization Program, begun in early May 2010, continued into 2018, with four units completed in February 2018. The program essentially came to an end in late 2018, with the last units completed in early November.

In addition to receiving reconditioned components (main generator, traction motors, air compressor, air brake equipment, etc.) the SD40N units received SmartStart systems, also from ZTR Control Systems. The rebuild also included refurbished cabs with new doors and seals, air conditioning, Positive Train Control capability, and completely rewired electrical cabinets. A major part of the rebuild was the installation of remanufactured engines with all applicable modifications to comply with federal government CFR Part 1033 (Tier 0+) emissions standards.

UP 1613 was completed with the NEXSYS system and was renumbered from UP 3372 on July 5, 2011, but carried the earlier SD40-2 designation, with a note that it was part of the modernization program. After the SD40N model designation was adopted in early July 2011, all previous units completed as part of the modernization program, going back to the first one, UP 1550, completed on May 4, 2010, were re-designated as SD40N units.

As of early 2015, the number series for the SD40N units were UP 1550-1782. Also, many of the units in UP 1800 and 1900 series were designated as SD40N. Other units in the 1800 and 1900 series had been renumbered pending actual rebuild, and were labeled as SD40-2. This was to clear their 3000-series numbers for use by UP's 8000-8308 class SD9043MACs, which in turn were being renumbered to clear their 8000-series numbers for use by new GE units.

Tom Mack wrote on October 24, 2013:

NEXSYS  is ZTR's locomotive control computer system. It is designed to replace the Dash-2 modules on EMD locomotives or can be used to upgrade a pre-Dash-2 locomotive to a Dash-3 microprocessor controlled locomotive as well. It also incorporates an advanced wheel slip system which increases adhesion significantly and thus allows the locomotive to produce higher tractive effort. The NEXSIS III-i also incorporates ZTR's SmartStart AESS system.

One thing to note about a microprocessor system like NEXSYS (other third party systems are QES-III from Wabtec/Q-Tron or TECU from TMV) is that they incorporate a microprocessor (computer) that allows the wiring to be simplified by eliminating the complex interlocking logic between relays and contactors. The system can be programmed to use digital logic inside the computer to control the proper combinations of relays and contactors to run the locomotive. They also simplify troubleshooting since they can do a self-check of all the relays and contactors to make sure the proper group of relays/contactors is picking up or dropping out, and if there is a problem, the system can identify the specific relay or contactor that is at fault.

Included among the earlier SD40-2s modified with NEXSYS was UP SD40-2 3459, renumbered as UP 1628 on June 17, 2011. It was later changed from SD40-2 to SD40N. UP 3459 received Operation Lifesaver lettering in May 1997. UP 3459 lost this special lettering when it was completed and fully repainted as UP 1628 with its completion as a modernized SD40-2 (SD40N).

MP15N, GP15N, GP38N, GP40N

Beginning in October 2013, UP began equipping some of its MP15AC and GP15-1 locomotives with NEXSYS. These locomotives also had their designation changed to MP15N and GP15N.

The first MP15N, UP 1459, was completed in June 2013. By the time the MP15N program was cancelled in June 2015, a total of 38 units had been converted.

The first GP15N, UPY 653, was completed in August 2014. With 31 units converted with NEXSYS, the program was suspended in May 2015 due to most of the GP15-1s being in storage. GP15N program restarted in September 2016.

The first GP38N, UP 680, was completed in May 2015. By August 2016, a total of 75 units had been converted to use the NEXSYS system.

The first GP40N, UP 9993 (now UP 1337), was completed in April 2016. A second unit, UP 1453, was completed in June 2016.

EPA Tier 0+ Requirements

These Part 1033 engine retrofit upgrades are being obtained from EMD, which issued an retrofit kit for both 710 and 645E engines, with the latter engine being what UP's SD40Ns have. These SD40N rebuilt locomotives comply with the federal Tier 0+ requirements.

The original federal regulations governing locomotive emissions became final in 1998, and went into effect on January 1, 2000, creating Tier 0, Tier 1, and Tier 2 emissions standards for railroad locomotives. These requirements were amended in 2008, and the designation was changed to Tier 0+, Tier 1+ and Tier 2+ to reflect the new stricter standards. These new standards were required on locomotives remanufactured after January 2010, and require that rebuilds of locomotives manufactured from 1973 to 1992 meet Tier 0+ standards. Locomotives built after 1993, which does not include any UP SD40-2s, have to meet the stricter Tier 1+ standards.

The following comes from a ZTR Control Systems web page that is no longer available.

The EPA issued new rulings affecting locomotive emissions in 2008. These rulings introduced significantly more restrictive Tier 3 and Tier 4 standards. The Tier 3 standards came into effect January 2012 and were met by advancing engine technology. Tier 4 standards become effective in 2015 and it is expected that these locomotives will require exhaust gas after treatment technologies such as Selective Catalytic Reduction (SCR). This newer regulation also includes more stringent emission standards for remanufactured Tier 0-2 locomotives. The new standards are known as Tier 0+, Tier 1+ and Tier 2+.

Locomotives built before 1973 are exempt from any of these standards. Remanufactured locomotives originally built before 1993 must comply with Tier 0+. Remanufactured locomotives built after 1993 and before 2002 must also comply with Tier 0+. The exception is those locomotives that have an intake air cooling system, which must comply with Tier 1+. All locomotives built between 2002 and 2004 must comply with Tier 1+ standards when they are rebuilt. Locomotives built between 2005 and 2011 must comply with Tier 2+ when they are rebuilt. The new rules also require all new and remanufactured locomotives to be equipped with EPA certified idle reduction technology.


EPA Standards for Locomotive Emissions -- from the EPA Office of Transportation and Air Quality web site.

40 CFR 1033 - Control Of Emissions From Locomotives -- Code of Federal Regulations (CFR) Part 1033 requirements.

Federal Register for June 8, 2008, pages 37096-37350 (255 pages) -- Published rule that created the Tier 0+, Tier 1+, and Tier 2+ designations. (see page 37121)

UP SD40Ns at The Diesel Shop -- An overall roster of UP locomotives; see Note N for the SD40N units.