10 August 2015

An accurate vehicle history usu-ally paves the way to a fast di-agnosis. Years of experiencehave reinforced this conceptagain and again. Sadly, manysupposedly difficult diagnoses

became difficult simply because no one tookthe time to verify vehicle history first.This column concerns unexpected electrical

interference and how it causes chaotic symp-toms and erroneous trouble codes. The boguscodes send unsuspecting technicians on diag-nostic wild-goose chases, frustrating them andcustomers alike. The case histories that followare a reminder that patience and persistencemay be the most important things in your tool-box. Don’t expect customers to remember orrecognize vital vehicle history right away. It of-ten doesn’t happen.

Civic Cell ShakedownThe first example is a 2001 Honda Civic thatmy buddy’s shop had been maintaining foryears. Trouble code 15-3 (side air bag, passen-ger side) began appearing intermittently.

There were no obvious causes in sight; the carhad no history of collision damage, do-it-your-self modifications, etc.This was a tough assignment because the

code occurred very randomly. To make mat-ters worse, the customer couldn’t rememberany telltale conditions or events that accompa-nied the code. Plus, the owner was unable toleave the car for a thorough diagnosis duringthe several-month period when the code wasappearing.Finally, my buddy got a lucky break. The

Civic arrived with the SRS light on and an Ap-ple iPhone sitting on the passenger seat. Thesight of the cellular telephone spurred him todig for more vehicle history. Here, the cus-tomer’s daughter began using an iPhone short-ly before the air bag code began appearing.The lady didn’t recall that her daughter was inthe passenger seat using the iPhone wheneverthe air bag code was set. My buddy clearedthe code one more time and urged the cus-tomer to forbid cellular telephone calls fromthe passenger seat. This advice eliminated thecode 15-3 for good. My buddy is still servicingthis Civic two years later and the code hasn’treturned. Other Honda specialists said theyhave run into the same code, under the samecircumstances.An electrical engineer gave me some per-

spective on cellular telephone usage in auto-mobiles. To grossly simply, a cell phone is a ra-dio transmitter; it transmits “radio” signalswhen you’re talking on it. Things get interest-ing when you compare its signal to other radiosignals—and to the antennas needed to re-ceive those signals. For instance, a commonantenna on an older car (AM or AM/FM ra-dio) was about 3 ft. long.However, cell phones transmit radio signals

at substantially greater frequencies than olderdevices do. It so happens that an adequate an-tenna for receiving a cell phone signal is only1 to 2 in. long! Consequently, there are count-less potential cell phone antennas on modern

Customers love to carry cell phones and other personal electronics

in their vehicles. But these devices, as well as the accessories re-

quired for their use, can raise havoc with on-board vehicle systems.

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DanMarinucci

dmarinucci@motor.com

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Something as simple as a poor fit between the terminalsof a common power port adapter (like the one shownhere) and a vehicle’s power socket can cause intermit-tent arcing across the terminals. The arcing, in turn, cancause a broad spectrum of harmful electrical noise.

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eliminated the symptoms and thetrouble codes.

One tech experimented with ahome-brewed EMI/RFI shield. First,he cleared the codes in the vehicle.Then he carefully wrapped commonaluminum foil around the customer’spower adapter. The customer drovethe vehicle for several weeks and nocodes appeared. But soon after re-moving the aluminum foil, the codescame back!

According to the electrical engi-neer, there are two potential sourcesof electrical noise from these powerport adapters. The first is intermit-tent arcing caused by a poor fit be-tween the power adapter and thepower port socket itself. This kind ofarcing generates a “broad spectrumof electrical noise,” he said. Some ofthose dirt-cheap power adapters soldby discounters fit very poorly, he fur-ther noted.

The other problem is that a poweradapter usually contains an oscillator,which creates unavoidable electricalnoise. As we’ve already seen, thatnoise can cause serious problemswhen it “infects” on-board electron-ics. Building in the necessaryEMI/RFI noise shielding costs mon-ey, the engineer explained. Thecheapo adapters simply lack theshielding that high-quality productshave. (Some discounters sell USB-to-power port adapters for just a fewbucks!) Also note that Subaru re-leased a bulletin that cited the risks ofusing cheapo power-port adapters.

So, don’t overlook cell phone usageas well as power adapters when diag-nosing electronics systems today.Where necessary, politely but firmlyexplain the potential consequences oftheir use to customers. Also, remem-ber that some power sockets are hid-den inside a vehicle’s console.

The more some things change, themore they stay the same. Years ago, Iremember people complaining aboutCB radio usage on vehicles equippedwith some of the earliest electronicignition systems. I heard that the en-gine would stall when someone oper-ated a souped-up CB radio. Now Iunderstand how that could happen!

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vehicles. If these short antennas re-ceive unwanted radio signals, we saythey’re picking up electrical interfer-ence. (The acronym RFI stands forradio frequency interference; EMIstands for electromagnetic interfer-ence.) This interference, in turn, mayraise havoc with on-board electronics.

The engineer emphasized that au-tomakers spend substantial moneytrying to cope with electrical interfer-ence. But it’s difficult for engineers toanticipate and address every potentialsource of EMI and RFI. For exam-ple, consider another factor with thesolid little Civic I just cited. That carwas designed long before cellulartelephone usage was nearly as wide-spread as it is today.

Power Port PandemoniumThe second example of electrical in-terference occurred on Mitsubishiproducts. Techs told me that theywere fighting bizarre, intermittenttrouble codes on late-model Mit-subishis. Among other features, thesevehicles were equipped with thepush-button start/stop setup and key-less entry. Like other modern vehi-cles, these had networked computersas well as tire pressure monitoringsystems (TPMS).

These techs said that Mitsubishiswere coming in with an illuminatedTPMS warning light and related trou-ble codes stored. Sometimes, theycleared the codes, performed exten-sive road tests and the codes did notcome back. Later, the same customerwould return with the same TPMScodes! Furthermore, there were vehi-cles with keyless entry systems thatsometimes didn’t start—the enginewouldn’t even crank. An instrumentpanel message appeared warning thedriver that the ignition key was miss-ing; related trouble codes were storedhere, too.

Eventually, someone noticed thatthese symptoms had something incommon with each other—anadapter plugged into the cigarettelighter socket or 12V power socket.Repeatedly they tried clearing thetrouble codes and removing the pow-er adapter from the vehicle. Doing so

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