Spoiler:

Read everything, if you want, but the gist of it is that the reason for the problems mentioned in the headline might be a problem with the connector to the throttle motor (damaged or corroded)…

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I went on a roller-coaster-ride today:

I dug myself deep into the ****, but I quickly dug myself out again, too:

S-Type 2004, 3.0L:

I had to remove the air-intake-manifold to be able to remove the cam-cover underneath. Suspected oil leakage there… When removing the air-intake-manifold I realized that the connector on the wiring-loom, that connects to the actuator of the throttle body what utterly gone – absolutely nothing left. Thus, then I put everything back together, I had to think of something, and I did find in my collection of parts a new connector, which I thought is similar enough after a few modifications. Hence I used that. When I was finished I wanted to start the car… - it was “unstartable”…And I had all kinds of error messages on the display, like “Engine System failure”, “DSC not available”, “Cruise control not available” and other un-pleasantries…

I turned to the internet. Looks like I am not the first one with that issue, but not many answers there. One idea was a “hard reset”(removing the cable from battery plus and connecting it via a cable with battery minus for 30 sec.) – but this did not change anything. Another good idea was checking the fuse for the throttle motor: It is fuse 18 in the engine compartment fuse-box. There are not many fuses, and only one 20A fuse, and that’s the one: But that was also OK.

Not much else I would find on the net other than “bring it to a dealer”… - yes, sure: as if they would know…

Btw.: I also used an OBDII scanner, but found no codes. I have to add that I used a cheap scanner for about AUD$15, which worked fine recently on my X-Type.

But with no help from the net, I had to put my “thinking-cap” on again…

The only thing, which I did out of the ordinary, was replacing that connector… - the connector, which goes to the throttle motor (in the red circle):

And before I removed the wires from the destroyed connector I made a mental and written note that the upper cable is RW (red-white) and the lower one is GW (green-white). I took special care, when sliding the pins into the new connector, that RW is on top… Then I wound cloth-tape around. When I finally placed that connector in the then installed air-intake-manifold I could not double-check that the RW cable is on top, because I wrapped it in that cloth tape. But since I had that problem now, I removed the cloth tape again to double-check… I dunno how, but I did it wrong! I mixed up the cables. Thus I fixed that – and the car started… - but it was running just enough to drive a few meters forward and back and the illuminated X-mas-tree of error messages was unchanged, plus, I could not even rev up to 3000 rpm (that is normally the cut-off point for limp-mode (restricted performance)).

At this point I thought already that I may have caused serious damage to some module by having mixed up the wires (=voltages…).

I checked the wiring diagram and saw that those 2 wires go from the throttle motor straight to the Engine Control Module. Oh no!

And still no codes on my cheap OBDII reader. Hence, I took out my more expensive (but still crappy) OBDII reader (from X-Tools) – and there they were:

P2118, P2119, P2135.

They all have to do with the throttle actuator control motor.

Hence, I dug my way thru to the connector again. The fault just had to be there!

I pulled out the makeshift connector and looked into the connector-end of the throttle motor, and there I saw it: one of the two pins was bend to the side.

OK, so I had improved the situation from a reverse-polarity-connection to “not connected”… Alright then! Note that you get the same effect, if those connections are corroded to the effect that they do not have contact anymore.

Thus, I did now, what I should have done to start with: I placed the connector pins (of which the plastic housing had disintegrated) into their counterparts inside of the throttle-motor-connector and I fixated them there forever by filling up that opening with RTV silicone. Close to those pins I have cut the cables and added a new inline connector, so that I can take it apart again next time… - problem solved – all error codes gone…:



In summary: I stuffed up in the first place, but in about 1 hour I “decoded” (solved) the problem…

 

Excellent on the fly repair. Always thinking

 

Excellent discovery and write-up, as always. One minor recommendation I'd like to pass along:

I'm very hesitant to use regular RTV around wiring. That vinegar smell you get is acetic acid, released during the curing process. I think it helps etch certain metals to allow a better bond, IIRC. Unfortunately, this same process can attack copper wiring, leading to conductivity issues, especially within a crimp.

I know some guys have used RTV plentifully on wiring with no issues. But I've also heard horror stories of guys finding degraded connections under the glob of silicone. I suspect there are different types of RTV with varying levels of acetic acid. I seem to remember bigger blobs causing more trouble. My hunch is the outer surface would skim over and stuff inside took a long time to finish curing. Reading between the lines, with a thinner layer, the acetic acid was able to dissipate quickly before it caused any damage.

Hope I didn't scare you. Things may be just fine. But if the fault ever returns, I'd want to check if the RTV caused any problems.

 

Duly noted. Makes sense.
Thus, if I have probs in that area again, I know why, and I have to find something other than RTV after removing the corrosion off the contacts.
Would roof & gutter silicone be a solution?

 

I think any kind of sealer would be fine, as long as there is no acetic acid.

 

Coming from the motorcycle world. I always coat every electrical connection I work on with dielectric grease. Sometimes:es called electrical contact grease.