Nasty relay failure ...

[sparky]

My 91 NA1 developed serious electrical problems recently. Symptoms included
- dead air con
- illumination lights in Climate Control Unit (CCU) even if ignition off
- the CCU would power on with ignition off
- battery going flat too quickly
- car would still start and drive but Check engine light and TCS indicator staying on

I measured battery drain current and found it was about 700mA which is about 10 times higher than normal.

After much fuse pulling. multimeter testing and head scratching I finally found the Blower Relay had failed (in 'Sub Relay Box A' under the bonnet). In fact the relay was warm to touch even when car off. Upon removal there was some melted plastic in the relay box, although fortunately not enough to prevent replacing with a good relay - phew!

Battery drain current now back to 90mA which is normal for my car (my aftermarket security system adds about 30mA) but Check Engine and TCS indicators still on.

After following the diagnostic steps in the Troubleshooting sections of the Workshop Manual I reached point where either the main ECU or TCS Control Unit (or both) were faulty. Fortunately I had a spare ECU on hand and after swapping it in the faults dissapeared and the car is now operating normally again. yay!
(but not happy loosing an ECU)

I'm not absolutely sure the two faults were related, but I suspect they were. The failed / shorting relay was sending 12V into many wrong circuits. My best theory is that somehow 12V got into the 'Service Check Connector'circuit and thus into the ECU where it damaged the ECU input circuit (I'll pull it apart later for a closer look)

My question (especially hoping for Kaz's views) is about relay failures ... do they happen 'spontaneously' as the relay reaches too many operations? how often do they occur? Should those of us with older cars (like - all NSX owners :) be thinking of replacing high activity relays as preventative maintenance?

As an aside this is only the second failure I've ever had in my NSX which I've owned since 2007 (the other was the the lid of my collant reservoir failing and blowing off in the engine bay - no serious damage). As the car is 26 years old I think that's damn good reliability record!

thanks in advance

[Pride]

Hi again sparky, the climate control unit is quite a common fault on the early cars as Kaz will surely elude too but the good news is he carries out a great repair service for them.
You can read more about this on his many blog entries about them of which here's one:

http://www.nsxcb.co.uk/entry.php?1926-A-C-CCU-Board-Audio-Head-Unit-service-01

Good question about the longevity of the relays though.

[Kaz-kzukNA1]

Hi, sparky.
Before answering your question, could you do me a favour for test purpose?
Could you switch off the Italic font style from your signature? I can do it but would like you to do it for the test purpose.
I had to approve your thread again and not sure whether it's caused by the signature section or the number of posts after long absence from the Forum.
I have a feeling that the admin may need approving any of your future posts without making any changes to your account as your other setting, etc seemed to be fine.
I could make small changes that won't affect your public view and then force all settings to be saved in case something not taking effect after recent upgrade but before doing so, I would like to try the signature font style first.



Back to the question.....
By the way, Pride, this is different from the cap leakage but thank you for referring to my blog....


It’s a mechanical relay and not SSR so at some point, it will fail.
If you check datasheet of any mechanical relay, you will find 'Life Expectancy' there.
For example, like min. 5 x 104.

If you calculate, you would think that it would survive for the life of the car but it depends on many other factors and not indefinitely.

Very unlikely for majority of them to fail at the same time because they are activated under different conditions.
By the way, if you have aftermarket devices that will affect the operation of the electrical circuit or current consumption, please double check that the relay (and of course the fuse) has enough capacity, life expectancy and the spec of relay is suitable for the targeted device as well.
Depending on the aftermarket circuit, you may need built-in diode/resistor inside the relay otherwise, it may cause side effect when the relay is switched on/off.
After all, there is a coil inside these relays, unlike the SSR.

There are many relays on any cars that will be switched on and off everytime when you turn the IG key into P2 ON regardless of whether you start the engine or not.
If you are saying it was the blower motor relay, then that’s one of them triggered by IG2 so even without starting the engine, it will be activated as soon as in P2 position.


Other relays that tend to fail earlier are the ones for the speaker amp, eng bay cooling fan (91-94 MT or any AT) especially if you removed the fan but kept the relay upside down (moisture short circuit), etc.

Not all of the relays have the same spec so can’t swap easily and without any labels on the lid, you won't know which relay is for what circuit but I carry one or two most commonly used relays on my NSX but mainly because I drive in the night regularly and running relayed circuit for HID headlight so different reason.


Kaz

[sparky]

Gudday Kaz,
I went to my profile but could not access my signature to change it! On my "About me" page I could (and did) update the "About Sparky" items, but the signature underneath did not have the little pen icon for editting...

Good news though. I am able to see/edit my posts immediately now, so I can fix all my spelling errors :)

Thanks for your thoughts on relays ... 50,000 operations sounds like heaps, although dividing by 25+ years of use that drops to about 2,000 per year. I guess the blower may be turned on and off a fair bit, whether heating or cooling. Although like most of us, my NSX isn't a daily driver.

Anyway I take you point that some relays get an easier life than others. I've got quite a few spare relays so I might go swap out my cooling fan relay (with the right type!)

Meanwhile I'll have a gawk at your blog about CCU repairs (as suggested by Pride)

(BTW I'm more than happy to be a guinea pig for debugging the signature issue if you need my help)

cheers

[Kaz-kzukNA1]

Since your latest post showed up without moderation, no need to change your signature font.
Looks like something to do with the numbers of post after long absence although I'm not 100% confident on that.
We'll see how it goes until next time it happens.
I couldn't find and don't have enough knowledge of this forum software on how to check the moderation log when a certain thread/post was held by the filter.


Kaz