Experiments respecting effects of radio frequency interference on Intoxilyzer 5000 64 series upgraded to 66 series. Intoxilyzer in need of maintenance. Nokia 3500 cell phone purchased at Walmart June 2009 used to make calls during various Intoxilyzer 5000 sequences. ACABA mode, 100 alcohol standard. When RFI applied during first Air Blank often results in “Ambient Failed”. When applied during first or second flying wings Internal Checks often results in “Unstable Reference”. When applied during subject test sequence often results in high readings. Breath subject is alcohol free at all relevant times. Intoxilyzer® is a registered trademark of CMI, Inc. The Intoxilyzer® 5000C is an “approved instrument” in Canada.