Electronic Power Steering (EPS) Issues

mopedmaster

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Oct 20, 2019
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I purchased at 2011 Z4 35i a little over a year ago from a local BMW dealership. Since the weather has started to warm, I've been having issues with power steering. Randomly as you are driving down the road the car will display "Steering Assistance Malfunction" . Initially this would flicker on and then go back off, and you could continue to drive. It progressed to flickering, coming back on, and then staying off until the car was restarted. Relatively annoying and a safety issue (should it drop out while in a curve for instance). Last week it stopped working 20-30 minutes into a drive. This week it doesn't work at startup.

The error being thrown is "D507 PT-CAN communication error". This error and the symptoms of a restart to fix match an EPS related voluntary recall campaigns that BMW NA had for 2011 1-Series and 2012 Z4's (12V302000 (BMW Recall Campaign 12V-302). This included an extremely small subset of vehicles. The vehicles that were included were based on manufacturing records related to some lot/lots of defective capacitors.

In the notice from BMW to NHTSA for 12V302000 (attached) it states the exact symptoms I'm seeing:
If a loss of power steering assist occurred, the driver would be alerted by the illumination of a warning symbol in the instrument cluster and also by the activation of an audible warning. At the next vehicle (ignition) start, the EPS unit could function properly (the warning symbol in the instrument cluster would not appear, the audible warning would not be activated). However, the condition may occur again.
On the control module's circuit board, the ceramic material of a capacitor was manufactured incorrectly. As a result, the capacitor's isolation resistance is out of specification. This can cause variations in the electric current. Variations in the electric current can result in a sudden loss of power steering assist.

I scoped the PT-CAN line on the EPS computer when it was working properly:
91369078_10216209491845651_5012537742819590144_o.jpg


And when it was malfunctioning:
91452614_10216209492205660_8857673683477463040_o.jpg


If you disconnect the EPS computer from the harness while the issue is occurring, the waveform returns to normal. There don't seem to be any issues with the transceiver on either side (normal looking ohm readings between PT-CAN lines from the harness as well as directly on the EPS computer). It looks like the voltage on both lines (which are slightly different and show no indication of short) drops and slowly rebuilds before dropping again.

Snippets of data from the EPS:
D507 PT-CAN communication error (FC 13)
Error frequency: 54
Environmental data at the first occurrence of the error:
Mileage 5456.00 km

So it looks like this has been happening since ~3300 miles, when the car was brand new and still under lease. I've only seen the error maybe 10-15 times (very intermittent) so it means that the dealerships have been clearing this error during service and pre-prep vs addressing. I have the full service history from each dealer that took care of the car throughout it's life, no mentions of the rack at all. After lease turn-in this car was flipped a couple of times before the factory warranty had expired.

I know this car was manufactured about a year prior to the recall lot/window, but the issue seems identical. I've engaged BMW Customer Relations to see if I can get any traction to have it included in the recall, or have them goodwill a portion/all of it. I dropped it off yesterday. The dealership has confirmed the issue and I'm waiting to hear back from them or customer relations.

Screen Shot 2020-03-31 at 5.34.23 PM.png



If it doesn't work out (not holding my breath) then I have an aftermarket warranty I can lean on for the repair. Plan C is either to refurbish my existing unit, or replace the motor/ecu (or entire rack) with a used unit. There is a company that will refurb in the UK as well. Cost wise - ~$1k for a used rack, $400-500 for a motor+ecu, $400-500 to ship off for refurb, or <$20 in ceramic capacitors (and the same work that would be needed for a used motor or ship-off refurb). Things would be a lot easier if the EPS computer wasn't attached to the motor on the rack itself.


Has anyone else had an EPS rack failure? Specifically 2011 models?
 

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  • RCDNN-12V302-5495.pdf
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Nov 10, 2018
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2011 BMW Z4 35i
$4000.00 for a complete replacement, ouch!
After having just gone through this all I can do is share what little I picked up a long the way. From what I can make out after reading up on EPS systems is they are pretty simple. Position sensor, electronic clutch assembly, processor and electric motor. High current draw can cause some terminal ends to corroded. Loss of power could disrupt the can buss communication. Another thing I can tell you is they are pretty easy to pull out of the car. Two bolts hold the unit to the front sub frame, two tie rod ends, the steering shaft coupler (don't forget to keep your steering wheel from turning once the shaft is disconnected, you don't want to damage your clock spring) and a couple of electrical plugs. If you don't move the location of the tie rod ends I believe you will be able to put it back into place without the need to have the front end aligned. So your decision to repair in place verses doing it out on the bench should be pretty easy. The link to the rebuild company has a great how to take your EPS motor off. The company I found in the UK can test and rebuild your EPS components. One of the symptoms was not being able to communicate with the EPS module. Your code is just that, no communication on the bus. I never made contact with the company but you may be able to ask them if your code would be one they would look for or not. From what I could make out from just poking around cost of repairs were around $400. It's the shipping to a from that adds up. Plus the time to ship is another concern. If you consider a used unit you will need to have some programming done for it to work in your car. Not sure how hard or expensive that would be. I found a used rack on EBay for around $900 but you have to ask yourself how long before you are right back where you started if you replace with used?
 

mopedmaster

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Oct 20, 2019
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I've seen a howto on a different site for an F10 where the guy went through the same process, but with the rack in the car still. He just disconnected the tie rod from one side, split the housing, etc. He did this to rip the motor from a pull-a-part place, and to install the replacement motor in his ride.

Splitting the rack while it's still in the car is probably the route I'll take if bmw/warranty don't resolve it. I do component level repairs regularly, so swapping all the capacitors out in the ECU after I have the motor off shouldn't be be a challenge. The worst part will probably be getting into the ECU housing without breaking anything, along with potentially having to remove any epoxy insulation (if they've doused the board with it). I can't see shipping the thing off to the UK. Worst case (if the cap swap is a no-go or it doesn't fix anything), I'll probably just try to get a used motor+EPS. I can do a used motor+EPS for less than the UK refurb, and as long as it was made after 2013 I would be comfortable with it. I have all the tools/knowhow to code a used EPS to the car, but the local dealer would probably only hit me for ~$140 tops to do it.

I should hear something tomorrow. I'll post an update.
 

fmorelli

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I'll be amazed if BMW comps the repair, though they might. Maybe if you are a long-time customer with a history of buying new BMW's. One trick, if it comes back negative, is to ask to speak with the regional BMW rep who looks at the case.

That said, from your post - your electronics savvy. Good chance you can pull the circuit board and do the repair. A multimeter and a LCR TC1 or the like should get you by. At least since it comes out pretty easy, you can quickly take a crack at it and see where it goes. First pass, time and money are on your side.

I doubt the board is quenched in epoxy - the repair shop would suffer similar challenges. Most epoxies do not loosen up until you hit a few hundred degrees, so it's not like fixing that would be a walk in the park for the company. You won't be able to test the board on the bench, but hopefully discrete components are few enough and you can check for failures and replace/upgrade accordingly. Let us know how it goes. Also tagging @RobbiZ4 and @NoQuarter who own Z4's and seem to like to beat their heads against electronics walls from time to time ;-)

Filippo
 

mopedmaster

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Oct 20, 2019
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BMW NA finally came back and essentially told me to go kick rocks, as expected. I'm attempting to address through aftermarket warranty instead. It will probably take a few days before I know something. If it doesn't pan out I guess I have a good excuse (especially with self-quarantine) to make a DIY of some sort...
 

mopedmaster

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Oct 20, 2019
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Aftermarket warranty came through on this. $100 deductible will be my out of pocket cost. Super surprised that it wasn't a huge hassle. I bought the warranty in December (10 months into ownership) and have put maybe 5k on the ODO since the 1k mi / 30 day waiting period. Warranty coverage is from 39k - 139k and includes items like steering rack, braking components, engine, trans, injectors, cooling system (including radiator+water pump), swirly bois, etc. The price quoted for the repair exceeds what I paid for the warranty contract. If I had taken advantage of financing, this warranty would have run me <$100 per month.

BMW dealer should have the parts next week, but no chance of a DIY/howto on this as there is no core charge/keep the parts option.