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Uh, er, no Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 5 Jul 2001 09:40:25
In Reply to: Aftermarket ECU vs. TCS, Dishwalla, Tue, 3 Jul 2001 21:13:40 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Basically, what Mowers said.
The TCS function is not on the same 'chip' as the ECU. The TCS function is spread throughout the ECU, ABS, and a box of it's own. What's more, the system is different depending on if it is a manual or automatic transmission.
Contrary to popular belief, 'limp home' mode is what the system is designed to do. TCS doesn't screw up. The TCS used a 'drive-by-wire' system - namely, the gas pedal doesn't connect mechanically to the throttle plate - there's a computer in the way. Well, kinda. In automatic tranny cars, a sensor on the pedal tells the EDU what the throttle position is, and a motor on the throttle body moves the throttle plate. On manual tranny cars, there is a mechanical linkage, but it only works when in limp-home mode.
So what's limp home? Hey, your gas pedal is electronic, with a sensor to tell position. Saab engineers being safety-minded considered the situation where the sensor fails. You don't want to have the throttle go wide open, but at the same time, you don't want the car to just die. So if the EDU and or TCS detect a sensor problem, it drops into limp-home mode - it limits engine power, so if the sensor on the gas pedal were to fail wide-open, the car wouldn't take off and be uncontrollable. At the same time, you've got enough power to get off the road and to safety.
The problem with the TCS is detecting a sensor failure. It seems that the thresholds for determining a failed sensor are pretty low. And simple stuff, like a little corrosion at the pedal sensor could cause the software to detect a fault. The other problem has to do with how limp-home works. In manual tranny cars, there is a vacuum valve that enables the limp-home throttle cable. If that valve dies, or the vacuum line leaks, that will drop you into limp-home.
If you want to eliminate the TCS, you can replace the ECU with one from a non-TCS equipped car. You will also have to replace the throttle body with a non-TCS version, and retrofit the gas pedal to add a cable. It has nothing to do with where the function lives. It's not like the TCS goes bad, and then makes the ECU crazy.
, Thu, 5 Jul 2001 09:40:25 <-- Viewing This Message, Thu, 5 Jul 2001 16:34:08, Thu, 5 Jul 2001 01:37:21
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