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Discussion Starter #1
Some technical opinions needed. I’m back on my 98 Bentley Brookland that had the alarm issue and limp mode problem in the gearbox. I’ve been dealing with these two problems since I bought the car in 2018.
The alarm unit is now ‘fixed’ after I sent the module off to be repaired. I can lock and unlock the doors remotely, but I still get a key read failure which does not seem to do anything other than trip the message on the cluster. My bigger issue is that I’m fighting with the transmission, which is still stuck in limp mode.

I’m still not able to read the TCM with my Omitec scanner. I swapped the TCM with a used one that I purchased, and it made no difference. I still have a limp condition. Not being able to read TCM codes on the Omitec might be a red herring as I have tried to scan several other cars (03 Arnage T, 96 Continental R) and it failed to access the TCM, yet these cars shift fine.

I did get a TPS code from the engine management system and as the TPS has an input for the transmission, I replaced it, along with the two wastegate solenoids which were broken at the ends where the vacuum lines connect. This did not make a difference, and the car is still not shifting out of 2nd gear.

I checked the wiring and I do have voltage to the TCM so it’s getting power. Could I have bought two bad modules? Do they go bad often?

It’s a head scratcher. I’m hoping that someone has experienced this as well and can provide input.
 

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Discussion Starter #4
When you removed the TCM backup battery what did you do with it?
I'm not sure what you mean by TCM backup battery. The TCM does not have one inside the unit

29560



If you mean the grey box that houses a battery unit it next to the TCM. I believe that this is some sort of memory module stores adaptations for the transmission based on the driving style of the driver. I read somewhere that if the battery goes bad, it can create problems but unplugging it will allow the car to run fine without it. It made no difference unplugging mine or when i swapped it out with one from a 2001 Azure which had the same part #
 

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Discussion Starter #5
Is it still sitting on your roof?
Ahh yes, we're talking about the same part. No it's on the back seat now. Still have TDS6000. I used it to confirm from the wiring diagram that the TCM has power and earth. I'm somewhat stumped by two things:

1) Why my omitec won't talk to any TCM (not just this one)
2) Whether I may have gotten two bad modules
 

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When shifting from parking to drive do you get a gearbox fault notice and/or beep for 1/2 second?
 

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Discussion Starter #7
When shifting from parking to drive do you get a gearbox fault notice and/or beep for 1/2 second?
Not usually. Right now I get a key read error and brake pressure but the car is buggy. There's no codes from the ECM aside from air con
 

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Look at this thread:
Any Idea what this is for
Hmmmmm ...Three wires to the battery module.....

I believe that this is some sort of memory module stores adaptations for the transmission based on the driving style of the driver. I read somewhere that if the battery goes bad, it can create problems but unplugging it will allow the car to run fine without it.
Incorrect.

"The presence and location of the Battery Back-Up Unit which is fitted to aid the retention of fault codes in the Transmission Control Module (TCM) on all North American specification Rolls-Royce and Bentley motor cars,"
 

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Discussion Starter #10
That's good info and may well explain why my omitec can't read codes from any of my cars. It don't know if itl will resolve the limp issue but a trip to batteries plus is in order
 

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You did not study the picture that I posted nor the wiring diagram.

There are THREE fuses for transmission control.

There are two sources of direct fused power to the TCM.

Upon failure of the backup battery, no power flows to the TCM for the keep-alive memory circuit, killing off the diagnostics and shift functions of the TCM.

This is the cause of your limp home mode.

Go find your TCM battery backup and clip off the harness at the case.

Get a crimp butt connector and join two of the wires together so that you can re-power that circuit.

If you looked at the picture, it shows the N.A. market TCM backup battery and the "rest of world" bypass connector UT13655PA.

In essence, you are making the UT13655PA from your old battery harness.
 

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Congratulations JR2 , even if this is not the reason, very impressed by your knowledge and stategy to search and dig and let's hope find.
 
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