40 CFR § 1033.112 - Emission diagnostics for SCR systems.

---
identifier: "/us/cfr/t40/s1033.112"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 1033.112 - Emission diagnostics for SCR systems."
title_number: 40
title_name: "Protection of Environment"
section_number: "1033.112"
section_name: "Emission diagnostics for SCR systems."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "U"
subchapter_name: "AIR POLLUTION CONTROLS"
part_number: "1033"
part_name: "CONTROL OF EMISSIONS FROM LOCOMOTIVES"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401-7671q."
regulatory_source: "73 FR 37197, June 30, 2008, unless otherwise noted."
cfr_part: "1033"
---


# 1033.112 Emission diagnostics for SCR systems.

Engines equipped with SCR systems using separate reductant tanks must also meet the requirements of this section in addition to the requirements of § 1033.110. This section does not apply for SCR systems using the engine's fuel as the reductant.

(a) The diagnostic system must monitor reductant quality and tank levels and alert operators to the need to refill the reductant tank before it is empty, or to replace the reductant if it does not meet your concentration specifications. Unless we approve other alerts, use a malfunction-indicator light (MIL) as specified in § 1033.110 and an audible alarm. You do not need to separately monitor reductant quality if you include an exhaust NO<sub>X</sub> sensor (or other sensor) that allows you to determine inadequate reductant quality. However, tank level must be monitored in all cases.

(b) Your onboard computer must record in nonvolatile computer memory all incidents of engine operation with inadequate reductant injection or reductant quality. It must record the total amount of operation without adequate reductant. It may total the operation by hours, work, or excess NO<sub>X</sub> emissions.