1995 Q with TCS that needs flushing

[mattd1979]

I'm getting ready to do a flush on the TCS of a 1995 Q this Saturday. The Q belongs to mikejax21 on here. The last time I did this was back in January of 2005 on my mom's 91 Q after swapping out the tcs assembly for one that belonged to Wes. I figured that I posted what I did exactly but apparently I just mentioned that I solved the problem and left it at that. The service manual tells how to bleed air out of the pump assembly but not how to bleed the hydraulic lines that feed from the TCS to the rear wheels. What I am going to do first is flush the pump assembly by connecting it directly to the battery using jumper wire to run it at 5 second intervals drawing in fresh fluid in while dumping out the old. But I will also need to bleed the lines that tie the TCS to the rear wheels. The service manual doesn't mention any thing to that affect and I don't have the car in front of me to see how the lines are run until tomorrow. I just want to have a mental picture in my head as to how I'm going to do this. Does anybody here have any ideas as to how to go about flushing the TCS-to-rear wheel hydraulic lines? Thanks

Matt

[mattd1979]

Never mind. After further studying of the tcs actuator, I found that the single line from the ABS to the rear brakes goes directly into the TCS actuator and then splits into LR and RR coming off of the unit and so I only have to flush the TCS actuator by manually providing voltage to the pump in 5 second increments to flush out the old and draw in the new. There is no direct connection between the brake fluid to the rear brakes from the master cylinder and that of the TCS fluid.

Matt

[mattd1979]

Do I still need to loosen the bleeder valve when flushing out the old fluid while pooring new fluid in? I know that it says to do that to bleed out air.

[mattd1979]

I've been studying the FSM and I thought I remember hearing from Q45tech years ago stating that when the TCS system goes into fail safe mode, the secondary throttle is only open 75 percent and that the engine's power output is reduced until the problem is fixed. I haven't found that mentioned anywhere in the FSM. I'm looking at one for a 95 Q as that is the year that I'm going to be working on. Do you think this issue was only for 91 to 93 models as far as the reduction in power output when in fail safe?

[Infinitiguy19]

I don't think that is quite right. When any one of the electrical circuits part of a Traction Control System )TCS) is malfunctioning the TCS stops working all together. The SLIP and TCS OFF lights both come on but the TCS Control Unit (CU) does not retain codes after the engine is tuned off.

[mattd1979]

I know. It is while it is running that it goes into fail safe and when it does, according to Q45tech, the power is reduced when in fail safe I guess to help prevent tire spin when on an icy/wet road. Not as well of course as it would if working because then the rear brakes would activate depending on which wheel is slipping. But anyway, the same principle as when the engine timing is retarded when the knock sensors are bad to avoid pre-ignition when there may be a lower octane fuel in the tank since the ECU has no way of knowing when to adjust when the knock sensors are not functioning. Again as a fail safe.

[qship96]

Who you gonna believe.....some guy on the internet or the official factory service manual ?????

[mattd1979]

I thought I remember reading it in my mom's 1991 Q45 FSM about the reduction in power output like Q45tech said (Remember, he was one that seemed to have studied the FSM the most and was very detailed. Almost too detailed.) but her car isn't here so I don't have access to that service manual and so I just have the 94-96 service manuals to rely on. I didn't mean for this to turn out to be a big deal, just was wondering if it was something that was later modified on the Q from 94-95 since I didn't see it mentioned in the 95 manual that is online.

[Infinitiguy19]

I hate to say it (no I don't )Matt but I think either you remember what Dennis said wrong or Dennis doesn't know how TCS works very well. (I hope a lawyer doesn't show up at my door for the latter statement!)

The throttle is always open unless the system detects at least one of the two rear wheels slipping. Then does the throttle close for a small period of time. Or the TCS CU just applies pressure to the rear brakes to do the same thing.

From what I know the 1994-1996 (G50) TCS CU possibly changed in software upgrades (To expect worse tires from the 1994-1996 Q45 (Enabling the TCS to come on sooner/faster). But who knows... I have a spare one so I may see if all the pins line up.

The Service Manual is not perfect nor is Dennis. That's why we must use a combination of the two while checking both facts for accuracy.

[willmoodom]

this is an interesting discussion. i myself am in fail safe. when i turn my car on you can here the tcs actuator vibrating a number of times and then stop resulting in the lights illuminating. i guess i need a swap out. so the brakes and tcs work on different channels?

[mattd1979]

Yes, the hydraulic circuits are separated.