Re: TCS limp home/bypass valve? - Saab 9000 Bulletin Board - Saabnet.com
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Re: TCS limp home/bypass valve?
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Posted by LesH (more from LesH) on Wed, 10 Sep 2003 07:23:04 Share Post by Email
In Reply to: TCS limp home/bypass valve?, Adrian, Tue, 9 Sep 2003 19:30:59
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Adrian, no one has responded yet, so I'll tell you what I know even though it's not a complete answer.

Read the recently posted TCS solution summary for more info.

The valve on the firewall is the TCS safety valve. The valve on the fender is the bypass (hooter) valve controller. They are the same valve on different brackets. TCS monitors their condition by checking the resistance across the contacts. If the resistance gets too high when they are hot (normal hot is about 30 ohms) you will get a TCS error; and if the safety valve fails you will get limp-home mode (not sure about the bypass controller).

I believe the bypass controller valve's function is to disable the bypass valve under certain conditions (such as LHM) but don't quote me on that.

The function of the TCS safety valve is to engage the emergency LHM cable to actuate the throttle. Normally, vacuum is applied through the safety valve to a diaphragm in the throttle body, keeping the LHM cable disconnected. When the computer wants to engage LHM (ie - it found a problem somewhere, most likely in the TCS safety valve itself) it opens the valve which dumps the vacuum and engages the cable so that you can drive the car.

Hope this helps, and also hope that anyone more expert can provide corrections.

Make sure your check valves are not getting stuck (should only be able to suck through them in one direction).

Les

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