Hairy McScary - Power Shrift attempting 3rd to 1st downshift - Page 2

goz007 · 05-01-2025, 06:40 PM

I would now also only drive it in sports mode & see how it goes like this & if it's good like this then every change or test u make to diagnose the issue is the key to then switch back & see if the auto mode is sorted, otherwise U will end up chasing your tail forever & if & when U do find the fix U will never know what it was.

AlCan · 05-01-2025, 07:14 PM

Hi Guys,

Just back from a two minute spin down the road (in Auto mode) to check out the Steering Angle possibility.

B*gga me, if it didn't throw a 3N1 on the way back, just about outside our driveway. But again, No DTC. So it seems more and more that this is a Command / Control problem more than Mechanical, as you say Peter B.

At first glance (not knowing what PIDs might be at issue) just checked Steering Angle and Direction. It all looked plausible. The steering wheel itself is about 3.5° off centre to the left. The SAS angle appears to be about 0.5-1° off dead straight, also to the left.

I doubt either of these slight offsets are enough to do anything, so this is becoming a real head scratcher.

Yes goz, I've been thinking about the battery possibility (or alternator, I suppose?), but at this stage, my feeling is it's too consistent. Those kinds of electrical problems tend to create a bunch of random problems - though I suppose the windscreen wiper could be another one. Could prove me wrong, I guess! I do have the '11 with a good battery, but I'm not there yet

. I've got a gammy knee at the moment and am supposed to "Rest" it.

I'm much more thinking like you say that the wrong EGR data could have a lot to do with it, so I'm planning to talk to Peter James, probably tomorrow. I've also had a look at the EGR Data and it seems to be all over the place. The EGR_ERR PID (I think, OTTOMH) goes as high as about 70%. (But at idle, when it's supposed to be open, the error is ZERO!) Various people and posts say it doesn't matter, but maybe, in this case, it does.

The common lack of DTCs for these downshifts points to it being a commanded changedown rather than the second best choice following an "Unable to engage Gear 2" fault, but Why!?

Like you say, maybe time to start driving in TT-mode between tests, as it's getting a bit frustrating.

Another thought along the electrical lines - there's a lot of chatter out there about bad Earth connections. Again, this thing seems too consistent, but what's your take on that possibility? Old wives tales, internet myths or valid science??

AlCan · 05-01-2025, 08:10 PM

Hi again Goz,

Thanks for your comments about oil temps. Very helpful and reassuring.

Thinking more... on the results of the driving around today, including the one testing the SAS.

I see a strong correlation with braking. Virtually all the testing today was without much braking, mostly natural (hills) or engine braking - and had no jump downs.

Both the two occurrences today were closely associated the light or moderate braking, during or just prior to the jump down.

Interestinger and interestinger ...

AlCan · 06-01-2025, 07:14 PM

Continuing along the Electrical line...

Looked at battery today. Label might indicate 5yo. Even so Battery Load Tester put it well into Green for 800CCA battery, still in the Green for a 1,000CCA. Spins the engine over very nicely. But could still be dodgy. Will let you know.

Also found four Wiring Harness Earth lugs approximately under the Air Filter box. Undid, cleaned and retightened.

And no difference...

But as you say, if I don't test and it's suddenly fixed, likely never know the cause.

I'm gonna get a vacuum gauge next.

goz007 · 07-01-2025, 09:58 PM

As for the earth question, i.m.o 100% can cause issues & the same as U describe the hotter the wires get the harder to move the current pushing IR through the roof untill the circuit fails....as for the battery, yeah like I said, I've seen it 2many times the most recent was that SZ 760cc testing as a good battery indicator in the battery also solid green(but really that's just a false sense of security as it's only looking@1cell)but CCA was testing around 640 but battery test matching(expensive well known brand)was saying good battery) also struck another one that sticks in my mind on a Mazda 800cc battery, battery testing good & showing 780cca green indicator green 12.8v@rest car would start & drive perfectly, drive for hours without any issues, park it in the sun(was hot & summer@the time) it wouldn't start, park in the shade & it was ok... checking battery when it had the no start issues battery was still checking good, eventually after many attempts to diagnose (left it@anthor mates workshop as he found the situation quite funny & wouldn't believe me-until it did it to him(it was his sparky who said battery is U/S we laughed at him, he laughed back at us-car was in its no start state-had been driven out of the workshop sat in sun all day & then wouldn't start, sparky said I bet U a carton of carona that I'll put a new battery in & it will start.... well he took home a carton of carona.) although both these car are different to your situation(also both these cars were different to each other as well) the point being that with these modern cars that run a high demand on the power supply from a battery can play havoc with there modules.... batteries do strange things & batteries aren't made like they use to be & aren't really made to last any longer than 3yrs.....i.m.o 3yrs smile & be happy as uve done well

AlCan · 08-01-2025, 08:13 AM

Hi Goz,

Thanks - yes, I'm looking at putting another battery in just to see what happens. Will let you know for sure! Hah, a heat sensitive car battery. Must have had a crack or loose joint inside. Lucky it didn't go BANG! I've seen the result of a truck battery that did that. Ugly, stinky mess! Lucky no one was nearby at the time.

Also, rang PJ yesterday. He sends his best regards. What a thoroughly decent and helpful chap. A Jag man. We had quite a chat. Sounds like he's doing well. Gave me 4 options, all very sensible, will send pricing. He thinks it might be a solenoid problem. Anyway, for now I'm going to drive in in Manual mode, as so far, that's been fine.

But it's all a bit weird. Manual gear changes must use different routines inside the TCM, or why don't they mess up sometimes too? Maybe they will... ;-(