HW2 to HW2.5 Power Assist / Steering Upgrade / Replacement Strategy

[Krash]

I’ve had two temporary power assist / steering failures about a year apart on my June 2017 S75D now at nearly 160,000 miles. On the first it just disappeared. But then after sitting for an hour, it was back, for months.

Recently, it disappeared but then seemed to come back slightly, then, after sitting, it was fine again.

I assume the units are sealed and not serviceable, because decades ago, with these symptoms, I would have suspected the fluid was low, checked and refilled it.

One strategy is to wait until it happens again, then see if the failures are getting more frequent. But if someone else is driving when it happens, that could be bad.

To replace it is only $405 in labor but the whole assembly is $3305. And if I’m going to replace it, since my car is pre the AP2.5 redundant power steering addition, I’d really like the upgrade.

My service advisor thinks I have part…

1060801-00-E

…and would normally replace it with newer part…

1070801-00-F

…but if Tesla will let him install it, he thought this part may be the HW2.5 redundant setup…

1459637-00-A

…but I was told here that the 145* part is a model 3 part, not the updated model S part, assuming there is one. And yet I see more evidence that the 145* part is a really older S part and that the 107* part shows up in the catalog as supporting the APH3 (HW2.5) and APH4 (HW3) so maybe the newest, either with that redundant power supply or at least compatible with it.

Anyone familiar with these parts? Anyone know where the control wires for that unit originate and whether there are two sets for HW2.5? It would be great if there is only one wire and the redundancy is handled internal to the unit.

 

[JamesS]

Hi Krash: I found my car didn't generate any service codes either. I also found that the failure of my power assist was caused by a broken power belt inside the steering gear. The belt showed signs of slippage at first, and that may be where you’re at with what appears to be an intermittent assist problem.

The assist is provided by an electric motor which runs a rubber belt which drives a sprocket that moves the steering rack back and forth. While the car's steering wheel is connected physically to the steering rack also, and can move the rack with physical effort, it is this electric motor arrangement that provides the 'assist', and also provides the steering for Auto Pilot or Full Self-Driving. This belt is not much bigger than the belt that drives the beater-bar in your vacuum cleaner. Imagine such a dinky belt being responsible for keeping your car on the road while operating auto Pilot or SFD!! However, that belt is not available as a separate part from Tesla, or the auto-parts dealers. You might find something on E-Bay, but that's about it. The part references you give are for the complete steering rack and pinion mechanism, including the electric motor and including that crappy 10 cent beater-bar belt. The whole setup must have been designed by a moron (losing the war for want of a nail).

If I’m correctly diagnosing your assist situation, you can expect the assist to cut out without warning and stay out, resulting in a road-side break-down unless it’s seen to forth with. Below is an image of what my assist looked like when I opened up the enclosed belt housing on the steering gear. The electric motor shaft is at the bottom, with the steering rack and sprocket at the top wrapped with the beater-bar belt.

ps gotta be wary of somebody called ‘Krash’ driving a car. I wouldn’t let you pilot my airplane either! Sorry, just had to get that out.

 

[Krash]

…the failure of my power assist was caused by a broken power belt inside the steering gear…

Helpful photos. Did you have to drop the HV Pack to get that out?