Is EMI a Credible Theory in the Toyota Case?

DN Staff

February 26, 2010

2 Min Read
Is EMI a Credible Theory in the Toyota Case?

With some news agencies raising the prospect that electromagnetic interference may be implicated in Toyota’s electronic throttle problem, including USA Today’s article this week Could Electronics Be What’s Causing Runaway Cars? EMI expert Daryl Gerke, who is co-owner of the EMI consultancy Kimmel Gerke Associates is getting his share of inquiries.

Here is the text from an email response he recently crafted based on a query from a concerned client who owns a 2009 Camry:

“We’ve done quite a bit of work with the automotive companies and suppliers over the years, and have had many attend our EMI classes (including several in-house classes.) As a result, we have a pretty good feel for their problems, constraints, and test requirements.

Lacking any hard data, I don’t have much of an opinion on the Toyota problem at this time. Yes, EMI is always a possible contributor, but I think it is pretty unlikely. The automotive folks are very aware of EMI issues and conduct extensive EMI testing — both at the module level and at the full vehicle level. They are also very sensitive to both safety and liability issues regarding potential EMI problems.

The automotive RF susceptibility test levels are upwards of 200 Volts/meter, which are the most stringent levels of MIL-STD-461. Pretty hard to exceed those levels in operation, unless you are in the main beam of a radar transmitter at an airport or military base.

As far as interference from iPods (one reporter’s suggestion) or even cell phones, any expected RF levels would be well below the tested levels.

As an engineer, I have many questions. For example, are the problems only associated with the CTS linkages? If only the CTS units are causing problems, that might seem to “rule in” the mechanical design and “rule out” other issues like EMI. Furthermore, what about hardware failures? Apparently the throttle is controlled by a small motor. Are the motors sticking or stalling? What about the motor drive electronics? And let’s not forget the software guys.

No, I’m not trying to pin the blame on anyone, nor am I trying to defend EMI. At this point, there are lots of possibilities, and EMI is only one of them. I do hope they get to the bottom of this soon. Safety is always a prime engineering concern, but in our increasingly complex world, unexpected things sometimes happen. Often the best we can do is sort it out, fix it, and try to learn from the experience.

PS - Disclaimer — I own two Toyotas cars — a 96 Avalon with 130,000 miles, and a 2004 4Runner with about 90,000 miles. Both have proved very reliable over the years. My advice? I’d keep the Camry.

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