Clutch Anticipate wire to '99-'02 41 PCM's

[BRAAP]

For Gen III LSx conversions with '99-'02 PCM's cable TB, using GM Cruise control, what exactly is the PCM doing with the "Clutch Anticipate" Switch, (the one that goes to pin 32 of the PCM, Blue connector and is grounded while the clutch pedal is released, circuit opens when the pedal is depressed)? The Cruise control is already using a Clutch Position switch as well as a brake switch, so what does the PCM want with the Clutch Anticipate? Is it just for the PCM to use for Torque management settings between shifts, or is it related to the cruise some how, etc?


What would be the results if the Clutch anticipate circuit was;

1) Not connected to anything.

2) Connected directly to ground with no switch, what affect will that have?

Thank you,
Paul

[mr.prick]

The "Clutch Anticipate" Switch has another name, the Clutch Pedal Position Switch.

[BRAAP]

Thanks. Have the schematics, 2 separate circuits inside one physical switch.

Just curious about the Clutch Anticipate circuit and what would happen if left open, or connected to ground, not used with a switch.

[mr.prick]

Open= Clutch Applied
Grounded=Clutch Released

Open turns off CC
I see no reason to ground it without using the switch for CC.

[BRAAP]

First off, thank you for you help, but this is where I am confused.
Having spent several hours over the past few days pouring over every diagram, LS1 tech discussions I could find, talking with Chevy Thunder, etc, I dont understand why GM is using 2 clutch switches to disengage cruise control?!

As I read the diagrams there is already a clutch position switch that is wired in series with one of the 2 brake switches, and as I understand it from my research, its sole purpose is to disable Cruise control when either the brake or clutch pedal are depressed, which leaves the question why the other "Clutch Anticipate Switch" for the PCM? If what you are saying is accurate, then what is the Cruise Control module doing with the Clutch Position switch in series with the brake switch?

I was starting to assume the role of the "Clutch Anticipate" switch was possibly for "Torque Management" between shifts like the auto trans cars are set up for, or altering ignition timing and IAC to keep the RPM from spiking/rising between shifts or when disengaging cruise when the clutch pedal is depressed, but I didn't want to assume, wanted to know for sure.

Using the diagram below,
Clutch switches;
1) Clutch Anticipate Switch, wired to PCM only, blue connector, pin 32.
2) Clutch Position switch that is wired in series with one of the brake switches that goes directly to the Cruise control module. Both the brake and clutch position are normally closed, both pedals released. Touch either pedal, circuit goes open disengaging Cruise control.








For this BMW LSx conversion, if I could physically get the GM clutch switch, (that has both clutch switches integrated into it) in the car, I would just use that but being as it is not going to happen without a lot of custom fab work, it would be much easier to just use a couple relays triggered off the BMW clutch pedal switch to function just as the GM clutch pedal switches, (even have the diagram drawn up already), but am trying to get around that if possible.

[BRAAP]

Got the wiring down, using the BMW pedal switches and a couple relays was able to mimic the GM brake and clutch pedal switches, now I would like to activate a "CRUISE" light when the cruise is engaged. Does anyone know how GM is activating the "cruise" light on the dash, or a which one of the wires to the cruise control module could be used to activate the cruise light without affecting the cruise functionally?

Thanks in advance,
Paul

[Taz]

With LS1-B PCMs in truck applications (Sierra / Silverado) the Cruise indicator lamp in the instrument cluster is activated via a Class 2 communication from the PCM.

As an example on ’99 - ’02 trucks - PCM C1 pin 58 (Class 2 serial data) connects to instrument cluster pin A5. This same PCM pin also connects to pin 2 of the OBD-II port, and to BCM C1 pin A12.

I use mainly truck OS and harnesses. Camaro / Corvette OS and harnesses may use a different pinout, but the principle of operation should be the same.


Regards,
Taz

[BRAAP]

My PCM is from an '02 Avalanche.
Just looked at a couple '99-'02 PCM wiring diagrams, as you stated shows C1-pin 58 as "Computer data-lines" "Class 2 serial data".

This brings a few more questions, if you don't mind.
1) Is this pin #58 also the the data line that feeds the instrument cluster info such as coolant temp for the coolant temp gauge, is it what triggers the "Change oil" indicator in the information center of the instrument cluster, etc?

2) Is the data being communicated part of a Can-BUS network?

3) What means are there, if any, to extract data such as "cruise light", "change engine oil", and any other info that is being communicated out of the PCM?

Thank you,
Paul

[Taz]

Hello Paul,

Regarding communication to the IPC (Instrument Panel Cluster) …


Direct communication:

• oil pressure (gauge)
• voltage (gauge)
• check engine oil pressure (light)
• low washer fluid (light)
• turn signal indicator (light)

PCM serial data communication:

• coolant temp (gauge)
• fuel level (gauge)
• Speedometer
• RPM (Tach)
• Cruise Control activated (light)
• transmission fluid temperature (gauge)
• change engine oil (message centre)
• check engine oil level (message centre)
• engine over-heated (message centre)
• low coolant (message centre)
• low fuel (message centre)
• reduce engine power (message centre)
• trans fluid hot (message centre)
• trans hot…idle engine (message centre)

BCM serial data communication:

• cargo lamp on (message centre)
• security (message centre)
• Tow / Haul indicator (light)
• high beam (light)

Plus many others ……..

Regarding your question about “extracting” the serial data - there may be a way with the proper interface (something that can mimic PCM / BCM communications protocol) - but that option is far beyond my humble abilities !!


Regards,
Taz

[swingtan]

Just a couple of things regarding this switch and the tune. I'm not familiar with this particular OS / Vehicle, so I'll speak/type from E38 experience. This may not have any relevance.....

The Clutch Position switch controls a number of tune related operations...

• Clutch Fuel Cutoff
• Clutch spark timing
• Exit of DFCO on clutch engagement
• Exit of coast down mode ( maybe.... )
• Exit of Cruise Control
• Change of the rolling idle control

Not using the switch will impact all of these items, some result in a very bad reaction. For example, if you simply disconnect the switch so the ECM thinks the clutch is always engaged, then the engine will stall if it is DFCO and you press the clutch. Shorting the wires so the ECM thinks the clutch is always disengaged, will result in no Cruise Control.

There are reasons why you may want to not use the switch in a track car, but for a street car, it's probably going to be better if the switch is wired up. I see that you are probably going to do that anyway, so this is just reference information.

Simon.