The People of America's Oil and Natural Gas Indusry

E15 and Check Engine Light Malfunctions (Take 2)

Bob Greco

Bob Greco
Posted October 7, 2013

It lurks on every car or truck dashboard, the little indicator light that indicates potentially big problems with your vehicle’s engine. If you’re like me, a glowing “check engine” light elicits a groan, a facepalm and maybe some choice words – if not instant fear check_engine_facepalm_reducedthat the engine might conk out right then and there. In any case a visit to the repair shop is in my future. There, my mechanic will try to figure out what the heck could be causing the “Malfunction Indicator Light” (MIL), to come on. It might be a problem, or it might be a false alarm, in which case you’re still out the time and inconvenience of a wasted trip to the mechanic. 

Things to keep in mind as we revisit the issue of E15 fuel and falsely illuminating MILs, because research indicates that fuel containing up to 15 percent ethanol could cause check engine lights to falsely illuminate.

As part of a comprehensive program on intermediate ethanol blends, the Coordinating Research Council (CRC) recently wrapped up an investigation on the subject. CRC researchers conducted a couple of screening studies (available here and here) that showed a small number of vehicle models on the road could be susceptible to persistent false MIL illumination when fueled with intermediate ethanol blends.

Based on these screening studies, CRC selected eight potentially susceptible vehicles for further testing under controlled conditions. Investigators found that the likelihood of triggering the check engine light was sensitive to ambient temperature. Three vehicles using E20 illuminated the check engine light at 20 degrees (Fahrenheit), and one vehicle using E15 had its check engine light came on, also at 20 degrees. 

The Energy Department’s Oak Ridge National Laboratory (ORNL) recently sponsored a similar study (available as a technical paper published by the Society of Automotive Engineers here).  (Again, we noted this study in January, before the CRC research was finished.)

Bottom line: ORNL researchers produced results that generally agree with CRC’s. ORNL measured engine parameters that influence MIL illumination as fuel ethanol was increased in 22 vehicle models and combined the results with information from the CRC screening studies to project the frequency of in-use MIL illumination when operated on E15. Average MIL illumination rates were projected to be about  0.1 percent for E15 across the entire fleet of 22 vehicles tested but higher in sensitive models. 

Two of the main conclusions (from the last page of the ORNL paper) are telling and bear repeating, because they support concerns that the auto and oil industries have been expressing for some time (emphasis added):

Results show that MIL illumination should increase with ethanol content, but the rates of illumination will vary significantly by vehicle model. Thus, experience for a given vehicle model may differ quite significantly from a fleet-average estimate of MIL illumination rates.”


“Some vehicle models do not appear to be at significant risk for a substantial number of MIL illuminations with E15 fuel, and a smaller number do not appear to be at significant risk even if E20 is used. One OEM (original equipment manufacturer) appears to be at higher risk of experiencing a significant number of MIL occurrences with E15 use than other OEMs.

 So what are the important takeaways from the CRC and ORNL research?

  • Not all vehicles are impacted. Some 2001 and newer vehicles operate on E15 without false MIL illuminations. But testing by CRC and ORNL has determined that some vehicles do not.
  • A few models that are sensitive to the triggering of check engine lights on E15 can potentially translate to a huge annoyance and unnecessary costs for the owners/operators of a significant number of vehicles on the road today.

When combined with the earlier CRC studies that identified potential engine and fuel system damage to millions of vehicles from the use of E15, the new CRC and ORNL studies add further cause for concern from the use of this fuel in existing cars and trucks.