VistaVette

Findlay, but I'm not sure what else I would have done in their position. I called Chevrolet customer service yesterday and made a complaint about the situation, they gave me an event number and said they'll escalate the issue. I don't like this one bit, it could potentially stop on me at any time.

LT1 Z51

Ugh...

Why does no one understand how friction works. Steering at stop is significantly harder than at movement. Steering while rolling while much easier than at stop is still significantly harder than at movement.

Did you know by 60 MPH you have little to ZERO power assist. At 30 MPH the wheel is quite easy to turn.

The only thing that is difficult when power assist fails is parking and low speed operation. In BOTH those cases your ability to BRAKE is great enough that you won't hit anything.

It's perfectly safe, and while uncomfortable and annoying it actually not a problem. I really wish people in general would stop saying the steering is impossible to turn or is unsafe as both of those statements are categorically FALSE.

BTW, I work in steering for a living, the Corvette system was a product I worked on at my previous employer ZF Steering Systems (ZFLS, now Bosch Automotive Steering). I still work in steering but now at Ford.

LT1 Z51

It's harder to steer when driving slowly and near end of travel because physics is working against you. See my other post, but basically over 60 MPH you have no power assist as is. you are driving the system entirely with your own force

These comments as an engineer upset me to no end. Your life is NOT I repeat NOT in danger. The car is difficult and uncomfortable to steer at low speeds without assist, however you can still stop the car safely with the brakes, therefore your safety is NOT in danger. At speed, the car will steer nearly normal, you will only feel a slight amount of increase in effort.

If your assist came back the code was more than likely for Voltage or for Temperature. Both of those faults are "healable" because the fault isn't a loss of assist, rather a "deration" of assist. At parking a deration of less than 70% will result in significantly higher efforts, while still safe it is extremely uncomfortable. If you had either of these faults replacing the system WILL NOT SOLVE THE ISSUE.

The Voltage issue would need the wiring and Battery inspected. The Temperature issue is unsolvable, the system to protect the electronics will derate. If you are in an extremely hot climate (over 100) you need to not do a lot of high effort (example parking) maneuvers in a short period of time. This will cause the system to derate. All EPS systems actually are effected by these two faults.

Yours is most likely one of the two healable issues above, or less likely a "bad ground" or "bad ignition" wire. The system will turn off if it loses power (bad grounds cause a loss of power) and the system will not turn on if it doesn't receive the ignition (or as GM calls it "Communication Enable") signal.

LT1 Z51

Foosh, you won't like to hear this, but.... This is SOP for all OEMs when it comes to EPS.

No one keeps more than 10-15 units in stock nationally because the parts are 1. highly specific to each model and 2. extremely expensive. Therefore no one likes to stock them.

You can complain all you want, and it won't change anything. The EPS suppliers don't even like making service stock and keeping it. They literally build 50-100 gears "every so often" and ship them to the OEM the OEM holds those until they are depleted entirely and then orders more. This usually happens when a rash of orders come in to have them replaced.

ersatz928

LT1 Z51 : What is the expected service life of the toothed belt in the rack?

LT1 Z51

The system is designed to last "2 vehicle lives" which is about 300k Miles.

Obviously systems in cars which has higher usage (think livery type cars) have an "extended" durability cycle and are usually designed to last 4-5 "vehicle lives."

Tensioning the belt is the most difficult and if the motor is unbolted from the rack system the gear is basically useless until it is retensioned (the motor mounting is how tension is adjusted, one of the bolts can "slide" when it is not fully torqued)

daixloxbmw

Thank you for your input. I am familiar with the physics and fully understand that greater steering effort is required at lower speed when power steering is absent. I have driven cars without power steering, however none of them had front tires as wide or sticky as my Grand Sport. However, when my power steering cut out while in my company's parking lot, at around 10-15 mph, I could not reasonably turn the steering wheel with two hands as I indicated in my original post. Is it possible to turn? Sure... if I was prepared for it, perhaps if I leaned into the direction of the turn with my body weight and used 75+% of my upper body strength... but that's just not realistic if power steering cut out suddenly at lower speeds during a spirited drive on some narrow switchbacks with no margin for error. Again, while I appreciate your technical feedback, I feel you are underestimating how much effort it is to turn the steering wheel. It required significantly more steering effort than other cars I've driven without power steering. And for the record, I am a healthy 35 year old man in decent shape and I struggled to turn the steering wheel more than an inch or so and that's with my feet spread out in the footwell in a wide stance for better leverage, which of course is completely impractical if you're actually driving.

Bob-G

I have been wondering if the Z06's have the same steering design and use the same components, and if so, if any of those folks have experienced the PS issues mentioned in this thread. I saw some threads on the Z06 Discussion forum that were related to PS "loss". I read through some of the posts and they mentioned a "duct kit" that was made for cooling the PS unit. After reading that, I wasn't sure it would be related to this issue until I read the above posts from LT1 Z51 where he mentioned that heat is one of the factors that cause problems with the PS. In any case, I have pasted two of the links (there are more) from the Z06 forum below;

https://www.corvetteforum.com/forums...ails-here.html

https://www.corvetteforum.com/forums...the-track.html

LT1 Z51

Bolded for emphasis.

In that scenario you should brake if you come across an issue. The power steering while uncomfortable is not unsafe. To say it is unsafe is FUD, and hysteria.

I do agree EPS in manual mode is harder than hydraulic, however that doesn't make it unsafe. The difference is surprising at low speeds, but not something you can't control by speeding up, or by stopping.

If you are driving and paying attention, then you should be able to manage the transition while driving. In a parking lot you have to do hand over hand, and yes, it will require a significant effort.

LT1 Z51

The Z06 has the exact same hardware as the base car and GS. Only the software changed. In 2018 I think there are some hardware changes, but I think only for the new ZR1 (which needed EPS housing modifications to make more room for a larger serpentine belt).

Regardless the failure modes of non-electronic component failure of EPS systems are by and large identical cross supplier, cross OEM, and in the industry. The specific criteria thresholds may be different but all EPS systems derate for Temperature and Voltage (both low and extremely high). The wiring and grounding issues also apply as these systems are pulling a maximum 60-110A (columns are less than racks).

So unless your EPS has an actual component failure most likely it is suffering from a temporary deration. Low vltage is due to not wanting the EPS to collapse the entire electrical system (a full 110A current draw at 8 volts would probably kill all the electronics and stall the car due to a PCM reset). High Voltage and Temperature are to protect the power electronics in the EPS. The EPS uses a 3-phase AC Motor and has 6 FETs which are used to convert DC to AC inside of Power Electronics (identical in function to the stuff you see in Hybrids) these FETs can only take about 120C before they start to "burn out" so the system derates to prevent that. High Voltage causes heat, ergo it is treated identically to Temperature.

The reason EPS feels much better now is that original systems uses DC Commutative Brush Motors, later systems used AC (or Brushless DC as people call them) Motors with "Trapezoidal" Control which isn't as smooth. Current systems are AC Motors with "Sinusoidal" Control and that means those FETs are switching at a rate of about 20kHz which you can imagine at ambient temp already generates a lot of heat. Therefore the EPS is EXTREMELY sensitive to over temp.

daixloxbmw

Also bolded for emphasis.

You and I have very different definitions of what we consider unsafe. Vehicles have 3 primary controls: steering, accelerating and braking and if 1 of those 3 controls suddenly fail or are severely compromised in certain situations, I consider that unsafe. To be clear, I'm not talking about fatal injuries but even parking lot fender benders would be considered unsafe. Apparently GM agrees with me because they refused to release the car back to me until the issue is resolved because, and I quote, "it is unsafe to drive".

Again, I have driven cars without power steering before and never had a problem with them. I knew they had no power steering and therefore I was accustomed to the heavy steering effort. The issue with my Grand Sport is different because even in Sport Mode, I can easily steer with one finger and to suddenly lose power steering at any point would be unexpected and cannot be easily and quickly accounted for. I think this "sudden and unexpected" loss of power steering is the part you're not considering. If my Grand Sport simply had no power steering at all, I may agree with your "uncomfortable but safe" comment but that's not the case here.

Just out of curiosity, would you consider the sudden loss of hydraulic assisted braking to be "uncomfortable but safe"?

VistaVette

First: Thank you for explaining the system and possible causes; I really do appreciate your knowledge and willingness to share it.

As far as these issues go; its just not acceptable that the car can just stop working like that. It has been very hot here in Vegas but mine happened at 4am, temps around 90 and I wasn't doing much in the lot except parking. GM tests these things in the desert and I'd assume they've accounted for our climate. Should I expect to possibly have this happen every summer ?

I've owned cars without power steering ('68 Vette among others) and the car was designed that way and I was aware of how it handled. I have no doubt that in an average driving situation I would handle it and the car would as well. BUT: I have no idea what this car would feel like or respond like when it just quits in a situation (other than the parking lot I was in); which could be any time. Murphy's Law says it will be at the worst time possible

daixloxbmw

Update: Dealership has also initiated a "TAK" (again spelling?), on top of the SPAK. The TAK is the technical and escalated version I'm told. The plan now is to wait 48 hours from the initiation of the SPAK (6/29 afternoon) to allow time for the other dealerships to respond back with whether or not they have the part in stock. If someone has it (unlikely), they will have to give it up and ship it to my dealership immediately. If no one else has it, then the issue will need to be escalated to a GM Rep to get involved and potentially pull the part off the assembly line. I will follow up tomorrow afternoon, which is exactly 48 hours after the SPAK was initiated.

LT1 Z51

GM and the dealership are covering their *** FWIW.

Cars are sold everyday with manual steering as the accepted failure mode.

Sudden loss has a surprise factor, and this factor can be very uncomfortable. However you should either be able to speed up and complete the turn or stop and avoid an obstacle. If a driver doesn't have two hands on the wheel it's technically misuse. Most suppliers and OEM design to one finger or hands off in regards to controllability. So yes I'd expect a person to be able to control a loss of assist in a turn if they had one hand lightly on the wheel. The issue isn't the car, it's the driver panicking and not doing the right thing. This however is a general problem with driving in the US, people are not trained how to drive. Car makers can't design to a driver who isn't paying attention.

To your last point, it depends. Regulations state you must warn the driver but they do not say we have to prevent the driver from operating the vehicle. If someone drives without brake assist they can do so and it is safe. Liability lies with the driver if there is a crash as he has been warned via a dash message.

LT1 Z51

After 5 lock to locks (if I remember GMs test spec correctly) the system can derate. The test I think is run at about 90C so that's pretty hot. But to be honest in the desert it's regularly that hot under the hood. So if you do 5 lock to lock type maneuvers in quick succession in a place like Vegas the system will derate.

At speed the engine bay is a lot cooler. So this really only comes into play at low speeds.

VistaVette

Based on this information I'd think the cars at the Ron Fellows/Spring Mountain race track would be seized up on a regular basis.

While everything you say makes sense it seems there is an issue with this system, possibly on '17's specifically. There haven't been any other reports that I could find from prior years and another member with this issue was told that the '17 part is new.

LT1 Z51

The cars on the track actually see less heat (where the EPS is located) than during parking.

Parking is by far the most brutal thing you can do to the EPS. Load on the EPS is high adding to the high temps (lots of current generates more heat) in addition shedding heat is harder because air flow is at a minimum.

Basically parking lock to locks abuse the EPS the most.

17's might have some modifications but the ZFLS/Bosch system is for all intensive purposes identical. They might change a few things mechanically but the EPS motor and ECU are the same (the one in the ATS is also identical).

Bosch builds from a "toolkit" and can scale the motors to be larger and the power electronics to be rated for slightly more amps but otherwise the units are electrically identical. All current ATS, CTS, Camaro, and Corvettes use the same EPS motor and ECU family. They have unique tunings but common SW.

VistaVette

It just happened again!!! Pulling into the bank, a 2 mile drive.

daixloxbmw

That's awful VistaVette. I hope your dealership can finally pull some codes from your car and acknowledge that you have a problem. Be safe.

daixloxbmw

Update: The Service Manager at my dealership has escalated my case to a GM Rep and the goal is now to pull a unit from the assembly line.