Tech II Bleed Procedure

[Schuby87]

I was able to borrow a Tech II to bleed the brakes. Now I have read online that there is an brake bleed procedure that the Tech II walks you through but I am unable to find it in any of the menus. In the Special Functions menu (where I have read it should be) there is only Automated Test and Solenoid Tests, and neither go through the bleeding procedure.

Does anyone have experience with a Tech II and know the procedure for bleeding brakes on a 98? I looked through the service manual and it doesn't mention the brake bleed procedure either.

[hoogiesngrinderz]

From BigE on LS1tech:

Just thought I'd post up some more information now that I've hooked it up. I think a lot of people could benefit from this in a search.

First, my problem turned out not to be in the ABS system. After initially hooking up the Tech II, it said to refer to the procedure in the manual to properly bleed the brakes. So I borrowed a service manual and read up on the system. After educating myself a bit, I performed a closer inspection of the master and discovered it was leaking into the booster so my problem was unrelated to the ABS block (GM calls it the EBCM [Electronic Brake Control Module] and the BPMV [Brake Pressure Modulator Valve] - BPMV is the block with valves and pump, EBCM is the controller bolted to it).

Second, looking in the service manual (HIGHLY recommended), the hydraulic circuits from the master cylinder to the wheels are completely uninterrupted when the ABS/TCS systems are not active. If you're not slipping or hard-braking, the system acts like any other non-ABS system. This is significant because the system will bleed like any other system. So if you bleed your brakes and it works well for a short period of time and then acts up, you could have air trapped in the ABS block that is being passed into the system when ABS or TCS is activated (slip, panic stop or when the system initializes after start up). Unless something really goes wrong, most people should not have to bleed the ABS when working on the brake system. However, I would highly recommend capping the system whenever you have to open it but aren't working on it. So if you're doing some work to the rear end and open the brake lines to do it, cap the ends of the lines if you're leaving it for a day/week/month. It will prevent air from traveling up the lines to the ABS block.

Lastly, the Tech II bleed is an AUTOMATED bleed process. The manual instructs you to pressurize the system to 30 psi (via Motive pressure bleeder or similar) before you start the process. Once that is done and you start the process via the Tech II, it will tell you to open X bleeder screw where X is whichever wheel it tells you. It then cycles the solenoids and pump in the ABS block to bleed the block and that particular wheel circuit at the same time. Once that completes, it will tell you to close that bleeder screw and move on to another one. You do that until all 4 wheels are bled. This is as far as I got since I discovered my problem was elsewhere. The reason I think this is important is that, not knowing it was a pressure process, I was hoping to use the Tech II to open the solenoids and then bleed the system with the foot-pump method. I didn't try it, but looking at the way the system works, I don't believe it would be an effective method. So if you have to do this, plan on having a pressure bleeder available.

I am no expert in the use of the Tech II or in the design of the ABS/TCS/brake system. However, through this problem, I have learned the above. I hope it helps someone else if they run into issues similar to those that I did.

[hoogiesngrinderz]

If you still want to go through with it, this is from teamzr1.com

Perform a manual or pressure bleeding procedure. If the desired brake pedal height results are not achieved, perform the automated bleed procedure below.

The procedure cycles the system valves and runs the pump in order to purge the air from the secondary circuits normally closed off during normal base brake operation and bleeding. The automated bleed procedure is recommended when air ingestion is suspected in the secondary circuits, or when the BPMV has been replaced.

Automated Bleed Procedure

Notice: The Auto Bleed Procedure may be terminated at any time during the process by pressing the EXIT button. No further Scan Tool prompts pertaining to the Auto Bleed procedure will be given. After exiting the bleed procedure, relieve bleed pressure and disconnect bleed equipment per manufacturers instructions. Failure to properly relieve pressure may result in spilled brake fluid causing damage to components and painted surfaces.

1. Raise the vehicle on a suitable support.
2. Remove all four tire and wheel assemblies.
3. Inspect the brake system for leaks and visual damage. Refer to Brake Fluid Loss or Symptoms - Hydraulic Brakes. Repair or replace as needed.
4. Inspect the battery state of charge.
5. Install a scan tool.
6. Turn ON the ignition, with the engine OFF.
7. With the scan tool, establish communications with the EBCM. Select Special Functions. Select Automated Bleed from the Special Functions menu.
8. Bleed the base brake system.
9. Follow the scan tool directions until the desired brake pedal height is achieved.
10. If the bleed procedure is aborted, a malfunction exists. Perform the following steps before resuming the bleed procedure:
- If a DTC is detected, refer to Diagnostic Trouble Code
(DTC) List and diagnose the appropriate DTC.
- If the brake pedal feels spongy, perform the conventional brake bleed procedure again.
11. When the desired pedal height is achieved, press the brake pedal in order to inspect for firmness.
12. Remove the scan tool.
13. Install the tire and wheel assemblies.
14. Inspect the brake fluid level.
15. Road test the vehicle while inspecting that the pedal remains high and firm

[Schuby87]

I have read both of those posts before. I tried the method in the first link and didn't have success. After activating the ABS while driving I started getting all the bubbles while bleeding. I was going to try the power bleeder/Tech II method but the website that gives that procedure looks like it is for newer Corvettes and the menu for the bleed procedure isn't available.

[Darren]

Brian (bri2203) you have any input on this? I know he is pretty good with a tech 2...

[hoogiesngrinderz]

The ABS on 1998 cars are on a different communication bus. Maybe that's the issue?


Did some more reading (since I have the 98 as well) and I saw that the DBC-7 system (99+ system I believe) is the one that needs the scan tool.

[Schuby87]

The ABS on 1998 cars are on a different communication bus. Maybe that's the issue?


Did some more reading (since I have the 98 as well) and I saw that the DBC-7 system (99+ system I believe) is the one that needs the scan tool.

I'm thinking the same thing. I've read through the brake section of the manual a few times now and there is no mention of using the Tech II.

[birdie2000]

I have nothing to offer other than I watched a friend use a Tech II to bleed the brakes on my old 2000 Cavalier to get out some stubborn bubbles and that is totally the way to go if you can get it to work. The thing practically bleeds itself. I'd use it on every bleed job if I was able to.

[Schuby87]

Expanding a bit on Mike's post...

The reason the brake bleed procedure isn't available for me is because my car is a '98. In '98, the Bosch 5.3 ABS unit was used then for '99+ the Delphi DBC-7 unit was used. The newer DBC-7 uses stepper motors to actuate the ABS pistons which is why it is able to cycle the solenoids and bleed the air out.

The bleeding procedure for a 1998 Fbody is outlined on page 5-38 in volume 2 of the service manual. It calls for pressurizing the master cylinder (to 35 psi! yikes!) and opening the rearward and forward ABS hydraulic modulator bleeder valve.

[hoogiesngrinderz]

I wouldn't ever pressurize to 35 psi, 20 maybe. I'm willing to bet there are some horror stories out there

[Schuby87]

Now the question is: where are the rearward and forward bleeder valve on the ABS hydraulic modulator? I haven't been out to the car to look, but I don't see an bleeder screws in pics on the Internet.

[hoogiesngrinderz]

Good question. After a bunch of reading....I still don't know I'd like to do a complete flush and put in some good fluid when the time comes