Hi, I work at a airport where we drive the E6 from the terminal to the parking lots. We are being told to not turn the shuttle on while we aren’t using it because it will break the electrical steering.
From time to time our EPS (electrical power steering) will go out and the steering becomes very heavy. It seems to come and go. If I leave the shuttle on, the EPS never goes away, only when I cycle the ignition.
I just wanted to get some input on this and see if anyone else may have had a similar issue with this.
Acek94 – you didn’t say what year your e6 is – it makes a big difference.
If you have the late model 2016+, are you getting the EHPS FAULT message? If so, turn the ignition OFF and then ON and your EPS should function normally. My driver gets that fault occasionally and I think it is because she turns the steering wheel while turning the ignition ON and there is an excessive 12V electrical load transient. I’ve never gotten the fault but then my arms are longer for an easier reach to the ignition switch.
Yes EHPS refers to electric hydraulic power steering which leads me to believe the GEM EPS software is adapted from “big car” electric power steering software. If anyone knows for sure I’m interested.
I wish I could tell you the year but I don’t know. It does display the EHPS message though. Some times cycling the ignition won’t help, but if you drive it for a while, it will kick back in. I’m being told by maintenance at the airport it’s because we leave the shuttle turned on and plugged in. I find this hard to believe, have you experienced something like this before?
2016-2018 Service Manual page 8.68 Note: “To conserve battery power, the EPS unit will shutdown 5 minutes after the engine has stopped if the key remains in the ON position. At this point the EPS Malfunction Indicator Light will illuminate to indicate the EPS has shut down and will set a fault code in Digital Wrench.”
The EPS seems to be fairly sophisticated. It’s continually running self-diagnostics and monitoring battery voltage, ground speed and engine speed. It has transient high current requirements beyond the capacity of the DC/DC converter so the 12V battery is used as a current buffer. I suspect these transients while turning the ignition ON are the cause of my driver’s EHPS Fault as I’ve never observed them in any other circumstances. My driver loves her EPS – basically couldn’t drive her e4 without it.
Another possibility is your 12V battery is losing its discharge capacity. It’s a plain AGM battery: https://powersourcebatteries.com/products/wpx14ah-bs-agm-battery which should be mounted in the passenger-side dashboard. Very easier to replace: take the dashboard top off, undo two battery cables; undo rubber hold down strap; and lift it out. You’ll spend more time looking for tools than replacing the battery. I recommend a full charge on the new battery before installing it to reduce the possibility of faults, etc.
Because I’m adding non-GEM accessories I’m installing a second identical battery in parallel to increase current capacity. I have only the one 3kw charger so I mounted it where the second charger would go. I doubt your maintenance crew would be interested in this upgrade but if they are I’ll send you pictures.
The thing is, the EPS only stays on if I don’t cycle the ignition off. Every time I turn it off and back on, the EPS will throw a code and sometimes it will go away and sometimes it won’t.
After re-reading the service manual, a tired 12V battery seems to be the most likely cause. The battery is tired because it’s not being properly charged by the DC/DC converter. The converter has four terminals: two 48V in and two 12V out. The 12V is for both vehicle power and battery charging. Therefore there isn’t a special “charge profile” for the battery and it’s either being under- or over-charged. Since the 12V battery is charged by the DC/DC converter while your e6 traction batteries are being charged means the under- or over-charging, both of which shorten battery life, is pretty much 24/7/365 in your work scenario. The marginal 12V battery adequately powers the EPS until the ignition is cycled in which case the marginal battery cannot sustain the EPS power-on surge (like my driver you are likely turning the steering wheel at the same time and/or the wheels are not pointing straight-ahead) and the EHPS Fault is displayed.
Like I said before, replace the 12V battery. And always park the e6 with the wheels straight-ahead and always wait until the full Ignition-ON sequence (ie, center gauge sweep, etc) is completed before touching the steering wheel.