GM Reverse Engineering

[The1]

im interested, just picked up a VX V6 with all the gear, need to do the brake fluid and bleed the abs, dont have a tech2, i have the commands to do pre VT ABS i will have to compair.

[VL400]

Iv never seen a mode6 before, I was expecting a mode 4 since it would be manually controlling the valves.

In PCM land mode 5 and mode 6 are part of the same task, mode 5 tells the PCM to enter in to download mode, and mode 6 is used to upload your own code to execute from RAM (this is part of how a VX/VY flash PCM gets read and written). Mode 6 frames are usually large as you need to upload an entire program as quickly as possible. The ABS module may do something similar for the bleed procedure, it may not be a standard feature .


There is mode 4 control stuff to compare with what you found from the tech 2 here if you want .. http://pcmhacking.net/forums/viewtopic. ... 60&p=27366

[Tazzi]

Hmmm, it does fire off about 10 or so of those large mode6 abs frames. But no matter what, I would have expected it to always "upload" the same frames to the abs module to perfrom the same action? Im always sending back the exact same messages to the tech2, but those frames constant change each time I perform the bleed.

The message length when doing the abs bleed is D8. Whereas, it seems to send off the same sort of message although the message length is D6, I get those ones when entering first entering the abs section in the tech2. Ill log in car again to what happens in car when first going into the abs section and see if those frames pop up again.

I just did this for an 03 & 04 VY and got the same sort of stuff. And also repeated for VZ, which did the same.

Cheers for that VL, didnt know that there were some mode4 stuff already available! Looks like its following the same trend with what I had, havent had a good compare yet.
Will be looking at the Transmission stuff this arvo.

[Tazzi]

And transmission mode4's...
Only one I couldnt do was gear control, wantd me to be in "Drive".. it was requesting table 3, although not sure which byte is the gear selector yet. Id assume that this would control what gear the car goes into?
But that covers all the tests the tech2 can do PCM wise..

Code: Select all

  -Shift Solenoids
           1-2 Shift Solenoid A
On: From Tech2: F7 6C 04 01 01 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D7
Off: From Tech2: F7 6C 04 01 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D8
Exit: From Tech2: F7 6C 04 01 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D8
           
           2-3 Shift Solenoid B
On: From Tech2: F7 6C 04 01 02 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D6
Off: From Tech2: F7 6C 04 01 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D8
Exit: From Tech2: F7 6C 04 01 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D8
           
            3/2 Downshift Solenoid
On: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 10 FF C0 00 00 00 00 00 00 00 00 00 CA
Off: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 10 00 C0 00 00 00 00 00 00 00 00 00 C9
Exit: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 10 00 C0 00 00 00 00 00 00 00 00 00 C9
           
             Gear Control
Tech2 requests the engine on.
“Select Selector Position ‘Drive’!” 
(Come back to this)

 
   -Torque Converter Clutch (TCC)
             TCC Solenoid
On: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 08 FF C0 00 00 00 00 00 00 00 00 00 D2
Off: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 08 00 C0 00 00 00 00 00 00 00 00 00 D1
Exit: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 08 00 C0 00 00 00 00 00 00 00 00 00 D1

             TCC PWM Solenoid
On: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 02 64 C0 00 00 00 00 00 00 00 00 00 73
Off: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 02 00 C0 00 00 00 00 00 00 00 00 00 D7
Exit: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 02 00 C0 00 00 00 00 00 00 00 00 00 D7

             TCC Apply
On: From Tech2: F7 6C 04 80 80 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D9
Off: From Tech2: F7 6C 04 80 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 59
Exit: From Tech2: F7 6C 04 80 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 59


  -Pressure Control Solenoid (PCS)
Clicking Increase…
From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 01 97 C0 00 00 00 00 00 00 00 00 00 41
From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 01 AE C0 00 00 00 00 00 00 00 00 00 2A
From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 01 C5 C0 00 00 00 00 00 00 00 00 00 13
From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 01 DC C0 00 00 00 00 00 00 00 00 00 FC
From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 01 E7 C0 00 00 00 00 00 00 00 00 00 F1
Exiting: From Tech2: F7 6C 04 00 00 00 00 00 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 00 00 D9

[Tazzi]

From what I can tell, the abs module doesnt respond to the big mode6 frames, Well, I didnt see anything sent back.

I think the tech2 keeps freaking out because it doesnt get a response... Should I expect a response? Even a simple "message received" frame from the abs?
Id imagine thats what the pcm does? Or does it send back the same frame?

Also found when requesting data from the abs module, it sets off the abs alarm.. and prevents you from requesting any more data until the cars is turned off then back on.
I noticed the tech2 sends off a mode4 frame before requesting any information right at the start.. might put it into some sort of diagnostic mode preventing the module from freaking out. Requesting the "active" abs data doesnt seem to bother the system.

[The1]

i can't remember was quite a while ago but this is what i logged with tech1a doing my brakes on my vs

LEFT FRONT
START
F9,60,4,FF,32,FF,22,0,0,0,0,0,0
STOP
F9,60,4,0,30,0,32,0,0,0,22,0,0

RIGHT FRONT
START
F9,60,4,FF,36,FF,22,0,0,0,0,0,0
STOP
F9,60,4,0,34,0,36,0,0,0,22,0,0

REAR
START
F9,60,4,FF,42,FF,22,0,0,0,0,0,0
STOP
F9,60,4,0,40,0,42,0,0,0,22,0,0

[Dylan]

Is it necessary to operate the ABS unit during bleeding? I thought the valves were open all the time untill there's a lock up detected?

[Dazza92VP]

if you've let air into the system it will need cylcing due to the fact that air can get trapped in the pump side and the check valves prevent it from being pushed out with normal bleeding procedures

[Tazzi]

i can't remember was quite a while ago but this is what i logged with tech1a doing my brakes on my vs

LEFT FRONT
START
F9,60,4,FF,32,FF,22,0,0,0,0,0,0
STOP
F9,60,4,0,30,0,32,0,0,0,22,0,0

RIGHT FRONT
START
F9,60,4,FF,36,FF,22,0,0,0,0,0,0
STOP
F9,60,4,0,34,0,36,0,0,0,22,0,0

REAR
START
F9,60,4,FF,42,FF,22,0,0,0,0,0,0
STOP
F9,60,4,0,40,0,42,0,0,0,22,0,0

Cheers The1,
Pity it seems they didnt keep the same structure for the newer models
And if they did, then my tech2 is just messing with me

Guess I wont know till a bleed procedure is actually performed and logged

[Dylan]

if you've let air into the system it will need cylcing due to the fact that air can get trapped in the pump side and the check valves prevent it from being pushed out with normal bleeding procedures

Thanks for that. I fitted a brake upgrade to my 94 VR Commodore and have never been happy with the pedal feel even after several bleeds. The master Cylinder was also upgraded so every chance of air in the ABS unit.

Is their a way to cycle it without a Tech 2?