Code of Federal Regulations Title 40. Protection of Environment § 40.1045.110 How must my engines diagnose malfunctions?

(a) Equip your engines with a diagnostic system. Equip each engine with a diagnostic system that will detect significant malfunctions in its emission control system using one of the following protocols:

(b) Use a malfunction indicator. The malfunction indicator must be designed such that the operator can readily see or hear it;  visible signals may be any color except red. Visible malfunction indicators must display “Check Engine,” “Service Engine Soon,” or a similar message that we approve. The malfunction indicator must go on under each of the following circumstances:

(c) Control when the malfunction can turn off. If the malfunction indicator goes on to show a malfunction, it must remain on during all later engine operation until servicing corrects the malfunction. If the engine is not serviced, but the malfunction does not recur for three consecutive engine starts during which the malfunctioning system is evaluated and found to be working properly, the malfunction indicator may stay off during later engine operation.

(d) Store trouble codes in computer memory. Record and store in computer memory any diagnostic trouble codes showing a malfunction that should activate the malfunction indicator. The stored codes must identify the malfunctioning system or component as uniquely as possible. Make these codes available through the data link connector as described in paragraph (g) of this section. You may store codes for conditions that do not activate the malfunction indicator. The system must store a separate code to show when the diagnostic system is disabled (from malfunction or tampering).

(e) Make data, access codes, and devices accessible. Make all required data accessible to us without any access codes or devices that only you can supply. Ensure that anyone servicing your engine can read and understand the diagnostic trouble codes stored in the onboard computer with generic tools and information.

(f) Consider exceptions for certain conditions. Your diagnostic systems may disregard trouble codes for the first three minutes after engine starting. You may ask us to approve diagnostic-system designs that disregard trouble codes under other conditions that would produce an unreliable reading, damage systems or components, or cause other safety risks.

(g) Follow standard references for formats, codes, and connections. Follow conventions defined in SAE J1939–05 (incorporated by reference in § 1045.810) or ask us to approve using updated versions of (or variations from) this standard.