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Mark N
Mark N, ASE Certified Technician
Category: Car
Satisfied Customers: 200
Experience:  Saab Master Technician, GM Technician, 30 years experience.
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SAAB: 5 automatic transmission, fuse B,10 A..blown..blow

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RE: SAAB 1999, 9-5 automatic transmission, fuse B,10 A and fuse 12, 7.5 A blown, what is causing these 2 fuse to blow?

Hello and welcome!


The 2 fuses you're referring to are power supplies to the Transmission Control Unit (TCM). Fuse B is switched power from the ignition switch, and fuse 12 is constant from the battery. Both circuits go directly to the TCM from the fuse box, so the problem is either internal to the TCM, or the wiring harness is pinched somewhere in between.


If you can take the glove box out, the TCM is mounted on the firewall directly in front of it. Unplug it and see if the fuses still blow. If they don't, you'll need a TCM. If they still do blow, there's short in the wiring somewhere. A common place to look is behind the radio. The harness sometimes rubs against the radio mounting box, or the dashboard supports on either side of the box. Look carefully at the harness for damaged wires all around this area.


Hope this helps! If any of this isn't clear, please feel free to write back. Thanks for checking in with us!

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