Newb Asks: Do we need a relay with the Electronic Power Assist Steering EPAS?

[Gregski]

I realize I have a thread on the topic, but I wanted to have a clear and concise question and answer on this topic. Since the Toyota Prius motor has an external controller with it, do we still need a relay for the fat white cables that run to that control box or does the box have a relay inside of it already?

[Gregski]

so I found this wonderful write up here: https://studebaker-info.org/Tech/Esteer/EPASPRIUS/epasprius.html

"The Toyota EPS only needs three wires to operate. An 8-gauge power feed with a 60 amp fuse supplies the main juice along with an 8-gauge ground (6-gauge or larger may be necessary for longer, trunk-mounted battery harnesses). Next, Pin 6 of Connector P8 is run to a fused, switched 12v source to trigger the system when the key is turned “on.”

"First and foremost, the factory fuse is 60 amps, so we’d recommend 8-gauge or larger wiring for the primary 12v and ground wires that power the ECU and motor. While this current draw is one of the highest you’ll see in most automotive systems, EPS operates at about a tenth of that in typical operation. Think of it like a hydraulic system, it builds maximum pressure and stresses the system most when the wheel is against something, like a curb or the steering-stops themselves, and cannot steer further. Next, the only other hook-up needed is to a switched 12v source that turns on with the ignition. Once wired, you’ll hear the ECU click its main power relay, and within a few seconds, the motor will come alive. You may notice that without any connection to a steering system, that the motor does basically nothing. The torque sensor needs to see a load on the steering shaft to begin its assist, so be sure to lock down the steering box/rack end of the assembly when testing the unit’s function."

so I am going to try and run mine without an additional relay, and observe and report back how it performs, if it drains the battery

[PatrcioEV-ATX]

so I found this wonderful write up here: https://studebaker-info.org/Tech/Esteer/EPASPRIUS/epasprius.html

"The Toyota EPS only needs three wires to operate. An 8-gauge power feed with a 60 amp fuse supplies the main juice along with an 8-gauge ground (6-gauge or larger may be necessary for longer, trunk-mounted battery harnesses). Next, Pin 6 of Connector P8 is run to a fused, switched 12v source to trigger the system when the key is turned “on.”

"First and foremost, the factory fuse is 60 amps, so we’d recommend 8-gauge or larger wiring for the primary 12v and ground wires that power the ECU and motor. While this current draw is one of the highest you’ll see in most automotive systems, EPS operates at about a tenth of that in typical operation. Think of it like a hydraulic system, it builds maximum pressure and stresses the system most when the wheel is against something, like a curb or the steering-stops themselves, and cannot steer further. Next, the only other hook-up needed is to a switched 12v source that turns on with the ignition. Once wired, you’ll hear the ECU click its main power relay, and within a few seconds, the motor will come alive. You may notice that without any connection to a steering system, that the motor does basically nothing. The torque sensor needs to see a load on the steering shaft to begin its assist, so be sure to lock down the steering box/rack end of the assembly when testing the unit’s function."

so I am going to try and run mine without an additional relay, and observe and report back how it performs, if it drains the battery



epasprius5.jpg

I don't think you need a relay for the main power line, but fuse it of course.