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I recently had a round of random crazy codes like this that all pointed to a voltage issue but it wasn't the battery. Turned out there was a power cable next to the driver's side SAI pump that had made contact with the pump and the chassis. The insulation had worn down causing a big short and random codes until the power cut out altogether. Replaced the cable and all is well again.

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Solved for now.


i put my head into the engine room this evening.

checked the fuse box in the engine compartment and  voila the fuse was blown. Changed it and everything fine.

Question remains why the fuse is blown.


i open the box with all the Relais inside and found one wire which didnt have a proper isolation. Dont know if this had some impact. 


Thanks for everybody supporting me to find the problem

Edited by ekstroemtj
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  • 2 months later...
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I'm considering replacing the nylon hoses with silicone vacuum hoses. Just to avoid revisiting cracks again a few years down the line.


Can anyone tell me what is the inner diameter hose I should get to fit the connectors?


Is there any reason why it would be a bad idea?


FYI, on a 957... There are no sensors warning of a failure. I found out when I couldn't stop at a red light and ended up in the middle of the junction being cursed at. All fun...



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  • 3 months later...

Common failures are all at the hose joints, mainly the cracking joint of the main pump spider hose and firewall cowl line to master cylinder. I used a self-fusing, silicone wrap tape and telecommunications-grade zip ties to wrap and tighten all the spider hose joints. The "Brake Booster Faulty" message should disappear after first pressing the brake pedal to start the car and the pump runs, to re-vacuum itself. Vacuum pump should not run while in drive.  

Edited by Zuffenhausen955
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On 4/9/2018 at 5:20 AM, Ignited said:

 Guys has anyone heard failure to replace these lines can cause hard shifting or banging in the transmission?

I don't think there is any connection. The brake vacuum system is completely independant. It doesn't even draw vacuum from the engine. On the 955 it is an electrical pump. On the 957 it is a cam driven pump.

Edited by KenTHK
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On 5/14/2018 at 10:06 PM, KenTHK said:

I don't think there is any connection. The brake vacuum system is completely independant. It doesn't even draw vacuum from the engine. On the 955 it is an electrical pump. On the 957 it is a cam driven pump.


KenTHK, there absolutely is a connection with the vacuum at the brake booster and every power-train system.  To test this, pull the vacuum hose off the booster while the engine is running.  You'll see what I mean.  The engine will severely misfire and run like crap.  Of course if your engine is throwing codes for random misfire and running like total garbage, that is going to make shifting hard to compute for the computer.  If your tranny doesn't shift right due to incorrect computer information then slamming, chattering, and such is expected.  So yes, the vacuum in the brake system even though boosted with vacuum pump still originates from the engine and directly affects the performance of the entire drive-train system. 

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