tcm to control SSR correctly

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Re: tcm to control SSR correctly

Postby Dazza92VP » Thu Dec 10, 2020 8:07 am

Mmm unfortunately I work for Isuzu and no one has any idea what’s wrong with this thing no ones had this issue with any of their trucks before and everyone I talk to about it is just backing away leaving me in the dark so I just had to try something to save it. I have a feeling that the it is holding both solenoids on at the same time to activate 1 solenoid takes only 5 amp but if it’s held it can draw up 22amps I don’t know what the internals of the TCM are rated for but that seems to be a lot for any poor pcb trace to handle
Thanks for the help though but if no one has any idea on how I can get this to work I don’t know what I can do

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Re: tcm to control SSR correctly

Postby Gareth » Thu Dec 10, 2020 9:00 am

I'd fuse the individual outputs to protect the TCM just in case...

That also may point you at the problem if you can get it to blow with regularity
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Re: tcm to control SSR correctly

Postby picvrss » Thu Dec 10, 2020 9:16 am

I have a feeling that the it is holding both solenoids on at the same time


Now, this is a bit worrying. A short between the drive lines to the 1,3,5 and 2,4,R solenoids would of course cause them to energise simultaneously (but incorrectly) and it would also screw up any valid feedback current sensing.

I'd have a very good look at that wiring loom again!

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Re: tcm to control SSR correctly

Postby Dazza92VP » Thu Dec 10, 2020 8:48 pm

I’ve tried fusing them before and after the tcm problem is that the solenoids draw any where from 5-20amps at hold but the tcm is not able to handle a hold of 20amps so it’s just popping the fuses purely due to load. We had the harness out completely stripped it even checked every pin is in correct positions found a couple of issue wires repaired them but still getting the issue on top of it this fault is completely random sometimes it happens straight away other times it’s 2,3,4 or 5000km

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Re: tcm to control SSR correctly

Postby Gareth » Fri Dec 11, 2020 6:42 am

What about a thermal circuit breaker at what ever the TCM is rated at, that will give some time for the current to settle down in hold before it blows/opens the circuit?

I know that, that is not fixing the issue but it would prove that the fault is in the box, which based on what you've said I suspect.
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Re: tcm to control SSR correctly

Postby picvrss » Fri Dec 11, 2020 7:29 am

With all the wiring checks you’ve done, I agree the box is most suspect. I’m curious to know whether, in all of those blown TCMs, was it always the one output driver that was blown? If it were always, say, the 1,3,5 solenoid driver, then that solenoid may have shorted coil turns or a short to its case.

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Re: tcm to control SSR correctly

Postby Dazza92VP » Fri Dec 11, 2020 2:13 pm

I could try that I suppose put a thermal unit in there. Yea every time it’s always the driver inside the tcm that blows out smokes it’s self and tries to unsolder itself from the board coupe of times it was the 2,4,R solenoid. We’ve put a coupe of new solenoids into it now thinking it was them and the brand new trans came with new solenoids on it as well

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