Climate control triggers 4WD light

[Darrel]

Hi everyone, might be in the wrong section but it is climate control related, I really need help here, searched and searched but turned up nothing, seems this is a new problem.

Car in question is a 95 V-spec BCNR33. The climate control recently developed a strange problem; when it is turned on, it will sometimes only blow air to the footwell regardless of changing through the modes/temp/AC on or off. But just let it run and it will eventually blow air to the correct channel selected and switching between modes then becomes normal.

Here's the weird thing, as soon as it directs air correctly, it triggers the 4WD/A-LSD lights (same thing if AC on/off).

I don't think it's the plastic gears cos there's no abnormal noise, crunching or anything, just the inability to change air direction when required, I suspect an electrical issue, is the climate control system connected to the Attesa somehow? Would sticky air control gears coming free cause a sudden/heavy electrical load to affect the Attesa?

Please help, guys, this problem has me stumped! Cheers in advance, guys!

Darrel.

[GTSBoy]

1 hour ago, Darrel said:

is the climate control system connected to the Attesa somehow

No.

1 hour ago, Darrel said:

I suspect an electrical issue

Yes, sounds like a wiring fault, like insulation damaged on 2 adjacent wires (one from AC, the other from ATTESA CU to dash, for example).

1 hour ago, Darrel said:

Would sticky air control gears coming free cause a sudden/heavy electrical load to affect the Attesa?

No. But it does sound like you have at least a version of the usual mode door actuator failure.

[Duncan]

I don't suppose you have any way to monitor the car's voltage when the issue occurs....it might be dropping and ATTESSA is the first thing to complain

[Darrel]

46 minutes ago, GTSBoy said:

No.

Yes, sounds like a wiring fault, like insulation damaged on 2 adjacent wires (one from AC, the other from ATTESA CU to dash, for example).

No. But it does sound like you have at least a version of the usual mode door actuator failure.

Hi @GTSBoy, cheers for that, I'm leaning towards an electrical fault in the climate control then cos when I got the car the control panel had been relocated into the glove compartment by the previous owner in Japan, I had it moved back and it's been problem-free for 3 years now, will take a look at it and check the door gears too and update. Cheers mate!

[Darrel]

18 minutes ago, Duncan said:

I don't suppose you have any way to monitor the car's voltage when the issue occurs....it might be dropping and ATTESSA is the first thing to complain

Hi @Duncan, did think of it too and was contemplating a daisy-chain ground cable from the trunk to the engine bay but I didn't notice any lights dimming or engine stuttering etc. I think my turbo timer might have a voltmeter feature though, I'll check and if not I'll install one, thanks for your input!

[GTSBoy]

22 hours ago, Darrel said:

contemplating a daisy-chain ground cable from the trunk to the engine bay

Why would you do that? The body is one big piece of steel wire.

[Darrel]

24 minutes ago, GTSBoy said:

Why would you do that? The body is one big piece of steel wire.

Thought it might help given the aging/deteriorating cables & connections. Not necessary then? @DuncanI've set my turbo timer to display real time voltage, will monitor and update. 

[GTSBoy]

Just now, Darrel said:

I've set my turbo timer to display real time voltage, will monitor and update.

That monitors the voltage where the turbo timer is connected. Will not tell you if you have a problem where the ATTESA CU is powered. You need a multimeter, manually probe the power connections while you wait for the AC to cause the light to come on.

[Duncan]

Agreed....but if it is what he has....

I was wondering if there was a voltage drop with the AC on, the ATTESSA is pretty voltage sensitive, particularly if the subframe earths are missing/broken etc

[Darrel]

7 hours ago, GTSBoy said:

That monitors the voltage where the turbo timer is connected. Will not tell you if you have a problem where the ATTESA CU is powered. You need a multimeter, manually probe the power connections while you wait for the AC to cause the light to come on.

I will try that, might you have a pin out for the Attesa CU? 

[Darrel]

7 hours ago, Duncan said:

Agreed....but if it is what he has....

I was wondering if there was a voltage drop with the AC on, the ATTESSA is pretty voltage sensitive, particularly if the subframe earths are missing/broken etc

I was thinking that too, which got me thinking if they shared a common earth or supply (of course that doesn't make sense 😅 )

[GTSBoy]

5 hours ago, Darrel said:

I will try that, might you have a pin out for the Attesa CU? 

Not for an R33. The R32 GTR wiring diagrams are posted on here, by me, sometime in the last couple of years. The ATTESA CU's are not the same, but the power and earth terminals might be.

[Darrel]

Hi guys,

A bit of an update, gremlin is still at large, checked voltage when the AC triggers the 4WD light, stable at 13.x, no voltage drop or surge. However, I took off the control panel and found some likely culprits causing the AC problems; an IC & a few caps, although I still don't know how it links to the Attesa. I've sent the control panel to a capable electrician, he said it looks promising. Any opinions, guys? Thanks in advance and have a pleasant weekend.

Regards,

Darrel.

[GTSBoy]

Well, there's probably nothing wrong with those caps, but they're easy to test for ESR and swap if needed, so go right ahead. That chip looks bad. Are the black contacts burnt? From heat?

Anyway, if they are damaged thus, then my original point remains valid. Wiring problem somewhere else (ie, outside the respective modules). Cause a short somewhere and the high current runs to places it will do damage.

[Darrel]

@GTSBoy will likely swap those 28 year old caps just to be safe. Not sure what the black stuff on the chip is, could be burnt as you said and likely damaged so will replace it too. Will get this fixed and get the AC harness checked, maybe something went wrong when they removed harness extension. Will update then, cheers!

[Darrel]

Hi guys!

Just wanna update everyone, I've found the issue.

Climate control system was faulty but totally unrelated to the Attesa fault. The PCB was corroded from the leaking capacitors and caused the erratic function, tried to fix it but no avail so I got a pre-loved unit and that fixed it but Attesa fault still came on.

Now the main issue. I noticed that throttle input would prevent the Attesa fault from coming on for example when you hold the gas constant at around 1500 rpm it wouldn't come on. Made me think if it had anything to do with TPS so I checked the TPS voltage at the throttle body. A long while ago when I checked it was about 0.4 almost 0.5 v, I thought it might have gone out of spec but it was exactly where I left it. So I checked the TPS signal at the Attesa CU and I was getting about 0.02, practically nothing. I proceeded to adjust the TPS till I got about 0.8v and checked the signal at the Attesa CU, I got 0.4v. I went for a drive and viola, no fault since then. I consulted Google and apparently it is quite common for the TPS signal to drop out in power FC. I'm not sure why causes this but I suppose the easy fix to this is to install a unity amplifier to repeat the TPS signal to the Attesa CU.

Anyway, I hope this helps our mates here facing the same Attesa fault gremlin, I don't know for sure but if it can happen to PFC I think it could happen to stock ECU's too. Hope this helps and cheers for all your input, thank you very much, guys!

[Duncan]

Good update

In that case, you should check the continuity of the TPS wire from the ECU to the ATTESSA unit. If it has high resistance, it is unlikely to be the only wire in that loom with a problem

[Darrel]

3 hours ago, Duncan said:

Good update

In that case, you should check the continuity of the TPS wire from the ECU to the ATTESSA unit. If it has high resistance, it is unlikely to be the only wire in that loom with a problem

Hi Duncan, yeah you're right, I wouldn't be surprised if I find a few signals out of spec, I'll get to it when time permits. Cheers for that!

[GTSBoy]

Yes, a dirty pin or a strained connection where all but a few strands of wire have pulled out of the back of a crimped pin sound like a reasonable cause.

Mind you....it's not as if there's supposed to be any current flowing in these wires. There shouldn't be any voltage drop. They literally are just voltage signals. Put 1V in at one end and fully expect 1V visible at the other.

I might suspect earth connections. If you have poor earths somewhere, then you get different CUs around he car thinking that 0V is in a different place, leading to the sort of thing you've observed.

And....for the love of Mike, do not just randomly install some sort of amplifier into a signal line meant to control a CU's decisions. That can only lead to worse things.

[Darrel]

@GTSBoy I believe I haven't been introduced to Mike 🤭🤭🤭

Jokes aside, you could be right about that, I'll check resistance of said TPS signal when I can get a mate's help. Cheers for that, mate!