Energizing the Audi A6 4.2 V8 Transmission Solenoids for the ZF 5 HP-24A

I’m analyzing the transmission functions on my 2000 Audi A6 with the 4.2 V8, so as to isolate a problem that most likely seems to be related to transmission solenoid #3, as far as I can intelligently infer from the symptoms and what I understand about the mechanical and electrical aspects.

So tonight I hooked my laptop PC up to the car and ran the amazing Ross-Tech software that talks to the car’s transmission control module and much else besides.

I like that the software displays the part number of the transmission control module, including the variant, e.g., BS or CT.

The software can run some output tests, by energizing each of the three simple transmission solenoids in turn for as long as I like. If I hear a clicking sound, that’s a good sign that the solenoid is probably opening and closing, and causing the corresponding valve to open and close, which is sort of the whole point behind having a solenoid.

I ran the test, and in all three cases, I heard an ongoing clicking sound. They all work, yay!

I next ran the test for the pressure control solenoids, which (I gather) have a more complex task that just being on or off. A variable amount of current flows through them, depending on what the control module wants the transmission to do.

In each case, I heard a click, which is as good as it gets, with these. Next, I checked the software for error codes … none found. So, no problems found there, either.

Next, I started the car and shifted into the various gears, with an emphasis on neutral, reverse and first, since first is the one with the problem. For neutral, reverse and first, the pressure control valves all seem to be in the same basic mode, and the solenoids are the big issue.

  • For neutral, solenoids 1 and 3 were energized.
  • For reverse, solenoid 2 was energized.
  • For first, solenoid 1 was energized.

That’s all correct too.

Pity … that would have been a relatively easy fix.

Still, I’m impressed that this car has these tests built-in. Very cool.

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