Under Pressure

 

 

This has been a week for TPMS issues—that’s AutoGeek for Tire Pressure Monitoring System. Many failures were attributed to the fact that the sensor batteries are getting older with each passing year. Battery life is directly related to the number of radio frequency transmissions which are affected by the system/sensor design and driving habits. Generally speaking, short drive trips with starts and stops can have a greater impact than overall miles driven. Those sensors have been rated at a 7-to-10-year life span but again, there are many conditions affecting battery life.

“What we’ve been fighting is a 2010 Ford Focus with a B2872 and a B287A code. What do you think it could be?” They ask.

Like I memorize every single DTC out there, right? Doesn’t everybody? So, I ask, “What are the code definitions?”

“The B2872 is a tire pressure sensor fault in general if the GEM module loses a sensor signal and B287A sets when the GEM module doesn’t get a response from all four sensors.”

“Okay,” I said. “Did you do anything to diagnose it?”

“We performed the relearn procedure and the car seemed fine after we road tested it. It came back three weeks later.”

“Okay,” I said, writing that down. I always jot down the notes and then review them for later. “Anything else?”

“We did a cold reboot of the smart junction box,” was the response.

“How did you do that?”

“We pulled the battery cables off and shorted them together for about a minute to drain the SJB’s memory.”

I jotted that down in my notepad. “Anything else?”

“The car has a dealer-installed car alarm but that was two years ago and this problem is fairly recent.”

I wrote that down.

“How long do the batteries last in the sensors?”

“That depends on driving habits for the most part. Manufacturers claim 7-10 years but I’ve been hearing that they last at the lower end of the window in city driving.”

“We replaced all the sensors on the vehicle but the car came back for the same problem and the same two codes.”

“At least you know what isn’t causing the problem,” I said.

They didn’t appreciate my comment. No one ever does. I remember a customer asked a friend of mine, “If a shop doesn’t send their technicians to training classes, then where do those technicians get their training from?” The response was, “Your wallet.”

“Do you think the Smart Junction Box could be bad? I mean—it monitors the sensors’ signals, right?”

“Correct,” I said, “But didn’t you say that the problem is intermittent?”

“Yeah—we even tried training the sensors in a different order and it worked fine.”

I jotted that down. “It acts up for the customer, right? But it doesn’t act up in your shop?”

“That’s right.”

“Is the customer driving the vehicle with an insurance tracking device, or a cell phone charger, power inverter—anything like that?”

“I don’t know—the guy is in the waiting room, so I’ll ask him.”

That is a missed step in the diagnostic process. Always check for aftermarket devices in the vehicle and always ask the customer about using them, also. Rod came back to the phone.

“The guy said not really.”

“Rod, it isn’t a tough question—yes or no? I don’t know what not really means in this business.”

“He uses a cell phone charger. But he also said he charges the phone while driving and sometimes the tire pressure system acts up with the charger plugged in and sometimes it doesn’t.”

“Most cell phone chargers don’t produce high levels of RFI all the time, Rod. It depends on the state of charge of the cell phone battery. The phone must be almost completely discharged in some cases for lots of RFI to be produced."

I heard Rod explain what I just said to the customer but Mr. Customer wasn’t buying it.”

“Rod, ask the guy if the charger is the original charger that came with his phone.”

After a couple of minutes the guy said that he couldn’t find the original charger and bought a cheap one.

“Here’s the problem,” I started, “Cheap chargers don’t carry CE, MFI and RHOS approvals. The U.S. market TPMS transmits data on 315MHz, while the European TPMS transmits data on 434MHz. Electronic devices not intended for U.S. markets may not be shielded properly for different frequencies, thus interfering with U.S. market devices—understand?”

I heard Rod tell the guy as best as he could but I heard the customer arguing. Rod came back to the phone.

“Is there anything else we can check? He doesn’t believe the charger could be doing it.”

“Yeah, Rod—you can disconnect the dealer-installed alarm system and tell the guy to drive the Focus for a while to see what happens. Sometimes, the interference can be caused by a module or ground on the vehicle. Depending on how bad the issue is, a dirty ground, improperly built ground shield or module can disable the system. Modules that have microcontrollers using clock circuits to create the timing pulses for the microprocessor may radiate RFI. I can go on, but how much does the guy want to pay you to diagnose it, Rod?”

Rod chatted with the customer. The guy decided to leave his car for additional diagnostic time. Rod set him up with a rental car and he left.

“Thanks for your time,” Rod said to me, “I’ll let you know what we find.”

And here the story may have ended except that one week later, that argumentative customer brought the rental car back with a TPMS problem that developed AFTER he plugged in that cheap, Brand X cell phone charger into the rental and it triggered a fault.

And he didn’t want to pay Rod for his diagnostic time because the car didn’t really have a problem—it was the charger.

“I don’t need customers like that,” Rod said.

“Really? Did you charge the guy to retrain the system the first time he brought it in?”

“Well, yeah, but—“

“Did you charge him to do a cold reboot of the SJB?”

“Well, yeah, but—“

“Did you charge the guy for the four sensors you installed that the Focus didn’t need?”

“Okay, okay—I get your point.”

I guess Rod got his training from the customer’s wallet, eh?

Closing up shop for the night.