Intoxilyzer E1 Through E7 Error Codes Explained
Updated August 26, 2026 · 6 min read
What's happening
An E-code on an Intoxilyzer 240 or 240D is what CMI calls an exception message. The instrument runs a self-check, finds something it isn't willing to test through, and displays a code. These are not generic "something went wrong" messages — each one names a specific subsystem, which means the code on your screen already tells you most of what you need to know about where the fault is and whether it's worth sending in.
The single most important thing to know: with one exception, an E-code inhibits the instrument from further use. It is not a warning you can test around. Plan on covering testing another way until the unit is back.
What each code means
These are the exception messages listed in CMI's Intoxilyzer 240/240D Operator's Guide.
- E1 — Error in fuel cell calibration. The fuel cell calibration data has been lost from memory, and the instrument's configuration has returned to its factory default settings. Expect your stored settings and operator IDs to need re-entering along with a full calibration.
- E2 — Hardware over range. The alcohol concentration in the sample exceeded the instrument's range of measurement. This is the one E-code that reflects the sample rather than a fault, and the only one that does not inhibit the instrument.
- E3 — Fuel cell sensitivity is too low to allow recalibration. The fuel cell can no longer respond strongly enough for the instrument to adjust itself into spec.
- E5 — Fault in the function of the breath sampling system. The pump and sampling path that pull breath across the fuel cell aren't working correctly.
- E6 — Fault in the temperature sensor controlling the fuel cell heater.
- E7 — Calibration attempted outside the allowed temperature range. The instrument must be between 59°F and 95°F (15°C to 35°C) to calibrate.
CMI's guidance is direct: if any E-type message appears other than E2, the instrument cannot be used and the service department should be notified.
Why E3 is the one you'll probably see
Across our service records, E3 is far and away the most common exception message on 240-family instruments, and it typically shows up the same way — during a calibration adjustment, on a unit that had been testing normally.
That pattern makes sense once you read the code literally. The fuel cell is the sensor that actually measures alcohol, and it is a consumable: its sensitivity drops with age and use. A calibration check compares the instrument against a known standard. A calibration adjustment then corrects the instrument back into spec. E3 means the fuel cell has degraded past the point where that correction is still possible — there isn't enough response left to adjust.
The practical read: E3 is not usually a setup mistake or a bad gas cylinder. It generally means the fuel cell has reached the end of its service life and needs replacement. There is no operator-side fix that restores a fuel cell's sensitivity. Before you send it in, it's still worth confirming you were using a standard within the accepted 0.040 to 0.110 %BAC range and a fresh mouthpiece, because ruling that out costs a minute — but if those were right, the fuel cell is the answer.
Two things shorten fuel cell life and are worth avoiding: blowing tobacco smoke through a mouthpiece attached to the instrument, which CMI warns can damage the fuel cell, and storing the unit in temperature extremes.
E5 and the noise that comes with it
E5 points at the breath sampling system — the pump that draws the sample across the fuel cell. Very often the unit tells you before the code does: a squeal, a whine, or a rattling noise on power-up or right after a test, from an instrument that has otherwise been fine. If you're hearing a new noise and then getting E5, those are the same fault, not two problems.
Like E3, this isn't field-serviceable. The useful thing you can do is write down exactly when the noise occurs — at switch-on, during the sample, or after it — and send that along with the unit.
The one you can actually fix yourself: E7
E7 is the exception in the practical sense, because nothing is broken. You attempted a calibration with the instrument outside 59°F to 95°F. This catches people calibrating in a cold vehicle in winter, in an unheated storage area, or shortly after bringing a unit in from a cold car.
The fix is to let the instrument come to room temperature and try again. Give it real time to equalize — the case warms up long before the inside does. Note that the operating range for testing is wider than the range for calibrating, so a unit that has been running subject tests fine can still refuse to calibrate on a cold morning.
E1 after a battery change
E1 means calibration data was lost from memory and the instrument has reset to factory defaults. Because it wipes configuration along with calibration, expect to re-enter your setup — stored operator IDs and site settings — after the unit is recalibrated. If you get E1, don't spend time reconstructing settings before service; they'll need doing again on the other side of the calibration.
What to do when a code appears
- Write down the exact code and what you were doing. "E3 during calibration adjust" and "E5 with a squeal at power-on" send us in different directions. The code alone is worth more than a paragraph of description.
- Stop testing on that instrument. Anything other than E2 inhibits the unit. Arrange coverage before you arrange service.
- If it's E7, warm the instrument and retry before anything else. That one is genuinely likely to clear on its own.
- Note the instrument's age and serial number. For a 240 or 240D this matters to the repair decision, not just the repair — see below.
- Call us to arrange service. We're a CMI authorized service center and can advise on a loaner where one is available.
Before you send a 240 or 240D in
CMI ended production of the Intoxilyzer 240 and 240D in June 2025. Support and service continue, but service continues for as long as repair parts remain available — which makes a fuel cell or sampling system failure on an aging 240 a repair-versus-replace decision rather than an automatic repair. Our guide on deciding whether to repair or replace an aging breath tester walks through how to think that through, including what to document for your DOT program.
When to call us
- Any E-code other than E2 — the instrument is inhibited and needs service.
- E3 during a calibration adjustment, especially on a unit several years into service.
- E5, or any new mechanical noise at power-up or during sampling.
- E7 that persists after the instrument has been at room temperature for a while.
- You need a loaner arranged so testing isn't interrupted.
Call the office at 513-891-0868 and have the instrument's serial number and the exact code ready.
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Still stuck?
If this didn't fix it, or the next step involves opening the case, recalibration, or anything that could affect accuracy — stop and call Foster. We'll get you sorted or schedule service.