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Cracking a Toyota's code

This Prius brake-by-wire system may be new technology, but old-fashioned troubleshooting led to the fix.
Wednesday, June 27, 2012 - 06:29
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For more than three decades, I almost always have looked forward to working on problems with new systems on a vehicle. After my first Prius brake-by-wire job, I’m a little more cautious these days!


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Verifying this brake complaint didn’t take long. There were no brakes. Well, maybe just a little if you don’t mind an adrenaline rush! Buzzer noises filled my ears and every warning indicator even remotely related to chassis or hybrid systems were ablaze when the vehicle was readied up in power-on mode. As a bonus, the brake pedal pulsed more radically than a car in a panic Antilock Braking System (ABS) stop.

I’m no stranger to hybrids or ABS, but because the two systems on this vehicle are married together for the benefit of fuel economy, I decided to invest a few dollars in the factory web-based info to print out most everything Toyota published on the subject. With a few mouse clicks (thanks to the National Automotive Service Task Force’s (NASTF) www.oem1stop.com) I’m inside Toyota’s Technical Information System website. After filling up a one-inch, three-ring binder to the point of bulging and running my printer out of ink, I decided to give America’s tree population a break and begin diagnostics on this very unique and challenging system.

Not wanting to perform brain surgery before taking the patient’s blood pressure and pulse, I decided to give the vehicle a routine visual inspection and Diagnostic Trouble Code (DTC) check followed by a thorough check for Technical Service Bulletins (TSBs).

Preliminary Findings
There were no TSBs on the symptoms. “Looks like I’ll be heading into uncharted waters,” I thought to myself. The 12-volt battery checked great at 12.65 volts, and every fuse under the hood and dash was good with available power. I did notice a body ground connection displaying some rust and corrosion on the left front inner fender.

On to the DTC check. My scan tool pulled three current DTCs. All three would come right back after being cleared with the tool. There also were no TSBs related to these DTCs. After this quick prelim/visual check I thought to myself, “I have a Mastertech with Toyota factory software. I’ve downloaded all the factory service information on the system. How hard can this be?” After all, I am an expert by the humorous definition. “Expert = a drip under pressure.” Yep, that’s me.

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