Re: ACC question - Saab 9000 Bulletin Board - Saabnet.com


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Re: ACC question
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Posted by sam96CS [Email] (#852) [Profile/Gallery] (more from sam96CS) on Mon, 19 Feb 2018 20:35:15 Share Post by Email
In Reply to: ACC question, skibumm100, Sat, 17 Feb 2018 07:07:28
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To answer your question about number of coolant sensors, there are 2. One located on the cylinder head between the intake runners for cylinders 2 and 3, and this sensor is used by the Trionic Engine Control Unit. The other sensor, which is used by the EDU, is attached to the end of the cylinder head above the transmission. This sensor informs the EDU which in turn operates the temperature gauge.

Looking at wiring diagrams I see no direct connection between either coolant sensor and the ACC. I see no connection between the Trionic ECU and the ACC. There is a connection between the EDU and the ACC. There's an orange wire that goes from the EDU to pin #4 of the ACC. There is a yellow/white wire that goes from the EDU to pin #38 of the ACC. This information is from wiring diagrams for a '97 9000 which probably is relevant to the '96 model year.

The ACC gets blended air temperature from a sensor located under the servo motor unit by means of 2 wires, a green/red wire going to pin #14 of the ACC and another green/red wire going to pin #32 of the ACC. I found an old post by Senon Don saying you can check the blended air sensor by disconnecting the ACC unit and checking the resistance between the green/red wires going to pins #14 and #32. It doesn't say what normal resistance should be, only that the resistance should decrease as the temperature increases. If you get a very low amount of resistance on a cold morning before starting the engine then that could point to the problem.

The ACC doesn't recognize defrosting problems because it lacks a cabin humidity sensor. I think the ACC's logic assumes the humidity is low, which often is correct on cold days. But on a humid day or when you have several passengers the humidity is higher than the ACC assumes. I just hit the defrost button and if that doesn't work fast enough then I increase the temperature and fan speed. Saab knew this is a problem, and the defrost solution I've described is in your owners manual.
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