I don't mean to start a controversy, just posting what my investigation has shown to me are the facts. I am posting this in hope of helping the next guy...

As we get hit with the TRIFECTA lights, I have seen well-intentioned folks post that it is RARE for the steering angle sensor to go bad and so we all go looking elsewhere. However, I now KNOW that such a statement is wrong.

The steering angle sensor is certainly a wear item, probably easier for it to go bad than the ABS module because it has moving parts which are vital to it performing its job. Yes, there are also those spring loaded tubes on the ABS but those don't wear out, and the tiny little wires don't move. Yes, the little wires break off [probably because of heat or whatever], but that's probably less common than an old steering angle sensor wearing out.

Anyway, the way the steering angle sensor works is that it has these 4 wire brushes which make contact against a wheel. The wheel spins when you turn and the brushes conduct and are used to [somehow] read that spin.

Well, those wire brushes wear out due to friction and when they do, they don't make contact with the disc anymore and the sensor can't report readings, resulting in... drum please... Trifecta.

Here are some photos of the sensor I took off my vehicle. I did not take apart the brand new one so I could compare because I did not want to risk the $300 invested in it. But I did carefully disassemble the old one.

You'll see in the close up photo of the outer pair of brushes that the wire brush on the left is significantly shorter (worn out) than its mate on the right and you'll also see that the wires in this brush are not all the same length. This is the problem that happens with age in these units... I guess you could try to repair them by replacing the brushes. If anyone wants to try that out, let me know. I'll ship you this thing. I have no use for it anymore. :-)
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2001 BMW X5 3.0i, Automatic, Gasoline