ELD malfunction codes.

What the single-character codes are

An electronic logging device (ELD) watches itself. Appendix A to Subpart B of 49 CFR Part 395 requires every ELD to monitor its own compliance with the technical rules and to keep a record of each problem it detects (section 4.6). Table 4 of that appendix gives the standard coding: seven letters for malfunctions and six numbers for data diagnostic events. The ELD stores the code in the one-character Malfunction/Diagnostic Code field (section 7.34), and that code appears in the ELD output file an officer can receive at a roadside inspection.

The distinction matters for the driver. A malfunction (a letter) means the device itself is no longer reliably compliant, and 49 CFR 395.34 then tells the driver to switch to paper logs and the carrier to fix or replace the device. A data diagnostic event (a number) means the ELD has spotted a data inconsistency, such as missing fields or unassigned driving. It is a warning that needs follow-up, not an automatic return to paper.

Malfunction codes P, E, T, L, R, S and O

The table gives the trigger described in the section of the appendix shown in the last column. Several of the triggers are aggregates across all driver profiles on the device, including the unidentified driver profile.

Data diagnostic codes 1 to 6

A data diagnostic event is recorded for the affected driver, and the ELD shows a separate visual data diagnostics indicator. It is not the same light as the malfunction indicator.

How a diagnostic turns into a malfunction

Several codes are linked. A power data diagnostic (1) becomes a power compliance malfunction (P) only when the understated driving time adds up to 30 minutes over 24 hours. An engine synchronization diagnostic (2) is recorded when the ELD cannot get updated values within 5 seconds, but code E needs more than 30 minutes of lost connectivity in a 24-hour period. A data transfer diagnostic (4) raises code S only if the device remains unconfirmed through the next three consecutive monitoring checks. Positioning has no matching number: the ELD writes the letters X, M or E into the latitude and longitude fields while it is short of a valid position, and sets code L once the cumulative 60 minutes is passed.

Unidentified driving (code 5) is the one that most often catches fleets by surprise. When more than 30 minutes of driving in a 24-hour period shows under the unidentified driver profile, the indicator turns on for every driver logged in to that ELD for the current 24-hour period and the following 7 days. It can clear when unidentified driving over the current period and the previous 7 consecutive days drops to 15 minutes or less. Drivers clear it by reviewing the unassigned records and claiming the ones that are theirs.

What a driver must do during a malfunction

Section 395.34(a) lists three duties. First, note the malfunction and give the motor carrier written notice within 24 hours. Second, reconstruct the record of duty status for the current 24-hour period and the previous 7 consecutive days on graph-grid paper logs that comply with 395.8, unless you already have those records or can retrieve them from the ELD. Third, keep preparing paper logs until the ELD is serviced and back in compliance. If you are inspected for hours of service during the malfunction, you hand the officer those manually kept records (395.34(b)).

For a data diagnostic event the only driver duty in the rule is to follow the motor carrier’s and ELD provider’s recommendations for resolving the inconsistency (395.34(c)).

What the carrier must do

A carrier that learns of an ELD malfunction, from the driver or on its own, must correct it within 8 days of discovery or of the driver’s notification, whichever comes first (395.34(d)(1)). A carrier that needs longer must notify the FMCSA Division Administrator for the state of its principal place of business within 5 days after the driver’s notice. The request must be signed and give a contact name, address and telephone number, the make, model and serial number of each ELD, the date and location of each malfunction as reported, and a statement of the good-faith steps taken to repair, replace or service the units. If FMCSA agrees it may allow an additional period and will give written notice of its determination, which is a final agency action. A carrier that files a complete request is treated as in compliance with 395.8(a)(1)(i) and (a)(2) until FMCSA decides, as long as the carrier and driver follow the rest of the section.

Worked example

A driver in a Texas panhandle stretch loses GPS reception for long periods. By the end of the day the ELD has logged 20 minutes of driving without a valid position within 5 miles of movement, then later 45 more minutes. The cumulative total is now 65 minutes in 24 hours, more than 60, so the device sets a positioning compliance malfunction (L) and writes E in the latitude and longitude fields of new events. The driver emails the carrier that day (inside the 24-hour limit), rebuilds today and the last 7 days on paper, and carries on with paper logs. The carrier then has 8 days from that notice to fix the unit or ask the Division Administrator for more time within 5 days.

Limits of this page

This explains the standard coding and the 395.34 duties. It cannot tell you whether your own ELD is on the FMCSA registered list, how your provider words its on-screen messages, or whether an officer will cite a violation. The appendix also lets providers add their own detection schemes under codes O and 6. We read the eCFR text of 49 CFR Part 395 (current through October 29, 2026) and Table 4 as printed in the 2015 Federal Register final rule, because the eCFR shows the table as an image.

Sources

Sources opened and read November 2, 2026.

• eCFR: 49 CFR Part 395 Subpart B, Appendix A, ELD functional specifications (current through October 29, 2026) (read November 2, 2026)
• Federal Register, 80 FR 78292, December 16, 2015: ELD final rule, Table 4 on page 78398 (read November 2, 2026)
• eCFR: 49 CFR 395.34, ELD malfunctions and data diagnostic events (current through October 29, 2026) (read November 2, 2026)