1997 F-Body ECM

[Terminal_Crazy]

It's all interesting mate.

I have the ABS manual for 1995 Z28 so I'll have a look. I wrote software to pull ABS codes years ago.
Anyone attempted to control the Retard function through the PCM pin. Would it respond to messages from a PC ?

Mitch

[sherlock9c1]

So are you talking to the PCM via the UART, and not the Class 2 data bus?

[In-Tech]

Hiya Tom,
Check your PM when you get a sec :)

[Tom H]

So are you talking to the PCM via the UART, and not the Class 2 data bus?

Yes or in fact talking with both. Interest on my part stems from "rough road data" and traction control spark retard. Both of these affect the TPU which is a specific area of focus with me.

Also, this list is about getting the tune right. If you want to log data other than regular GM stuff, modifications to the descriptors can have the ALDL spitting out data at a reasonable rate.

-Tom

[NomakeWan]

It's all interesting mate.

I have the ABS manual for 1995 Z28 so I'll have a look. I wrote software to pull ABS codes years ago.
Anyone attempted to control the Retard function through the PCM pin. Would it respond to messages from a PC ?

Mitch

The spark retard request isn't done over serial data, it's done via a "dumb" signal on pin C12. You just pull it high (connect to 12V). So if you engineer a way to connect pin C12 to +12V at will, there's your ASR spark retard.

Tom, that was an absolutely fantastic post about ALDL communication from the OBDII PCM above. Absolutely awesome stuff. As to your Arduino interface for ALDL, is this something that could be used in place of, say, an FTDI interface? Or is it limited to manual commands via the Serial Monitor in Arduino IDE? I suppose more accurately, I should ask if your Arduino setup exposes itself as a serial port at 8192 baud. If so, I'd love to see your design. I've got quite a few little 5V arduino boards laying around so that'd be yet another thing I could mess around with.

[Terminal_Crazy]

The spark retard request isn't done over serial data, it's done via a "dumb" signal on pin A23. You just pull it high (connect to 12V). So if you engineer a way to connect pin A23 to +12V at will, there's your ASR spark retard.

Excellent. Thanks for that.

Mitch

[NomakeWan]

The spark retard request isn't done over serial data, it's done via a "dumb" signal on pin A23. You just pull it high (connect to 12V). So if you engineer a way to connect pin A23 to +12V at will, there's your ASR spark retard.

Excellent. Thanks for that.

Mitch

Okay so, I had a look at some pin diagrams from my FSM, as well as the ABS/ASR manual for 1995. There's some interesting discrepancies.

Regarding the ASR Spark Retard, the 1995 F-Body pinout posted earlier in this thread claims it's on A23. Both my 95 Y-Body FSM and my 94 Y-Body FSM say it's on C12, as Tom H stated a few posts ago. Sadly while my 1992 ABS/ASR manual lists ECM-side pinouts (useless since 1992 was a totally different computer), my 1995 ABS/ASR manual does not list pinouts as it was a generic manual for B/E/K/Y cars, so it only lists the EBTCM pinouts and not the PCM-side pins they connect to. So I couldn't confirm that way. But two FSMs say that it's C12, and Tom says it's C12, so I'm inclined to believe that it is, in fact, C12. Which would leave me to wonder what the heck A23 is.

Additionally, as a side note, the pinout that was posted earlier in the thread claimed that pin B22 is "TCC TEMPERATURE SWITCH," Circuit 585, Tan/White wire. But my Y-body FSMs claim that B22 is "CRUISE ACTIVE SIGNAL," Circuit 396, Lt Blue/Black wire. This appears to be the only actual discrepancy between wires I've seen. While I could chalk this up to F-body vs Y-body, that's a pretty massive difference in function, and one that as far as I'm aware has not been documented.

[sherlock9c1]

But my Y-body FSMs claim that B22 is "CRUISE ACTIVE SIGNAL," Circuit 396, Lt Blue/Black wire.

Hopefully without taking this thread more than a few posts sideways, what does the PCM do in response to "cruise active"? Does it change auto transmission shift behavior?

[Terminal_Crazy]

On My PCM Connerction Printout which seems to match my '95 Z28 with 16188051 PCM - (It's not 100% reliable as it was probably off a 95 corvette )


C12 is listed as NOT Used
A23 Orange/Black circuit 463 is listed as Traction Control Spark Retard Request

Probably depends on year or PCM


Thanks
Mitch

[Tom H]

The spark retard request isn't done over serial data, it's done via a "dumb" signal on pin A23. You just pull it high (connect to 12V). So if you engineer a way to connect pin A23 to +12V at will, there's your ASR spark retard.

Hi, Looks like I messed up the pin number... it is A23 as you state. There seems to be an option to do traction control over the ALDL. I suspect it didn't work too well and was put on the shelf... still in the code though. I don't know much about nitrous oxide, but if spark retard is needed in those applications, the whole thing might be of use? Otherwise it is just some un-used code.

-Tom

[Tom H]

Okay so, I had a look at some pin diagrams from my FSM, as well as the ABS/ASR manual for 1995. There's some interesting discrepancies.

Regarding the ASR Spark Retard, the 1995 F-Body pinout posted earlier in this thread claims it's on A23. Both my 95 Y-Body FSM and my 94 Y-Body FSM say it's on C12, as Tom H stated a few posts ago. Sadly while my 1992 ABS/ASR manual lists ECM-side pinouts (useless since 1992 was a totally different computer), my 1995 ABS/ASR manual does not list pinouts as it was a generic manual for B/E/K/Y cars, so it only lists the EBTCM pinouts and not the PCM-side pins they connect to. So I couldn't confirm that way. But two FSMs say that it's C12, and Tom says it's C12, so I'm inclined to believe that it is, in fact, C12. Which would leave me to wonder what the heck A23 is.

Additionally, as a side note, the pinout that was posted earlier in the thread claimed that pin B22 is "TCC TEMPERATURE SWITCH," Circuit 585, Tan/White wire. But my Y-body FSMs claim that B22 is "CRUISE ACTIVE SIGNAL," Circuit 396, Lt Blue/Black wire. This appears to be the only actual discrepancy between wires I've seen. While I could chalk this up to F-body vs Y-body, that's a pretty massive difference in function, and one that as far as I'm aware has not been documented.

Ignore my earlier message, looks to need a bit more study. -Tom

[Tom H]

As to your Arduino interface for ALDL, is this something that could be used in place of, say, an FTDI interface? Or is it limited to manual commands via the Serial Monitor in Arduino IDE? I suppose more accurately, I should ask if your Arduino setup exposes itself as a serial port at 8192 baud. If so, I'd love to see your design. I've got quite a few little 5V arduino boards laying around so that'd be yet another thing I could mess around with.

I need to explain just a bit...
I took the standard Arduino library named "SoftwareSerial" and made changes to it. SoftwareSerial is a software based half duplex UART, thus it is all you need to communicate with ALDL. Mods I made were intended to reduce external hardware. I changed the interface to include another parameter that controls how the output is configured. Instead of the SoftwareSerial constructor which had a bool option for normal/inverted, I pass an unsigned which sets the uart as

0 NORMAL
1 INVERTED
2 OPEN_DRAIN
3 INV_TX

On the bench you don't need protection from transients, static and general mayhem. In this case with my code, just connect pin 2 and 3 of the nano to the aldl and you are done. If working in the car, you want a tougher tool so there is an interface I will publish that will buffer things up. I have not exhaustively tested the "hardness" of the interface but it should be plenty tough. To make it a bit easier on me, I will send out the code for the buffered version only unless there is a request for the other.

Here is the hardware...ALDL_IF.JPG

The modified version of the library code is called SoftSerial and you load it in you Arduino working directory. Code is in SoftSerial.zip. The so called sketch I wrote to drive this operates at 115,200 baud. The code down converts to the 8192 you want. Since I am essentially debugging, I set it up with commands. They are listed over the serial link when you open up your serial port. For quick here are the commands:

Serial.print("S: Suspend scheduler messages\n");
Serial.print("R: Resume scheduler messages\n");
Serial.print("T: Transmit a message to PCM\n");
Serial.print("0X: Place in ASCII mode\n");
Serial.print("1X: Place in Hex mode\n");
Serial.print("0L: Line mode off\n");
Serial.print("1L: Line mode on\n");

If you know C++, it will be easy to make this thing dance in any way you like. Otherwise it just dumps out the scheduler messages until you ask it to stop or send it something to do some test you have in mind.
I plan to add a few lines and parse such that it is one message per line.
If you do want the simple/no interface version, you need to change the line:

SoftSerial PCM_Serial(2, 3, INV_TX); // RX, TX, operational mode

to read

SoftSerial PCM_Serial(2, 3, OPEN_DRAIN); // RX, TX, operational mode

Including some sort of base code for the sketch for you to mod as you like

-Tom


PS: Hook it up ant try these two commands

s
T F4 66 03 20 00 20 01 20 02 20 03 20 04 20 05 20 06 20 07

The second command should dump out locations $2000 through $2007, in my case gives a reply

F4 5E 03 00 F7 BE B9 28 43 29 20 89

[NomakeWan]

Hopefully without taking this thread more than a few posts sideways, what does the PCM do in response to "cruise active"? Does it change auto transmission shift behavior?

It does, yes. There is a separate shift map for the 4L60E for cruise control active mode. The PCM has four base shift maps--Normal, Performance (triggered by momentarily grounding pin C13), Manual (triggered by moving shifter to 1), and Cruise (triggered when cruise control is on; unknown whether it's a high or low signal as the FSM doesn't specify).

On My PCM Connerction Printout which seems to match my '95 Z28 with 16188051 PCM - (It's not 100% reliable as it was probably off a 95 corvette )


C12 is listed as NOT Used
A23 Orange/Black circuit 463 is listed as Traction Control Spark Retard Request

Probably depends on year or PCM

I mean, if the PCM came off a 95 Corvette, then I can unequivocally say that the pin for TCS Spark Retard is C12. That's what it is for the 94-95 Corvette. A23 is listed as not used. Tom H likewise said that his disassembly of the 96-97 F-Body PCM suggests it's C12...or A23. So now it's rather confusing. A mystery I'm sure will be solved in short order.

There seems to be an option to do traction control over the ALDL. I suspect it didn't work too well and was put on the shelf... still in the code though. I don't know much about nitrous oxide, but if spark retard is needed in those applications, the whole thing might be of use? Otherwise it is just some un-used code.

-Tom

I see a probably related switch in the 1994-1995 PCM: "ASR PCM SEND ALDL ASR REQUEST" at 2026 bit 02. It's disabled on all my calibrations though.

[kur4o]

Tom H,

great write up, it doses clear some of the unknows so far.

About the traction control on 94-95.

There is 2 differnet type of usage incorporated in the code. Analog and digital.
The analog is used on the y-bodies only. They have some crap bosch abs module.

The pcm sends pwm encoded signal of tps to ABS via pin A12[needs confirming]
Abs request spark retard from pcm via a frequency signal at pin A23??[needs confirming].

There is also second analog system to request traction on.
Put B+ to pin c12. It is analog on/off switch. Not sure where it is used. ??B-bodies.

The digital system is used on f-bodies.

The abs sends some message to pcm via ALDL bus, Requesting spark control and retard on/off.
The pcm sends scheduled messages to abs with some engine parameters.


On the ALDL bus there are some messages scheduled for dumping.
F0 is broadcast message with bus master id.
Others are some passive data send to other modules. It is very unlikely there is a 2 way communcation between modules.
Mode 7 is used if a module request data from pcm.
AS used in y-body ccm to pcm. There the ccm is the bus master and request data from pcm, then interprets the data and send it to other modules.
The 40 41 is extra theft system used on y-bodies only.

[Terminal_Crazy]

Chilterns 93-95 Wiring diagrams 5.7L VIN P 1995 vehicles

show on Connector A
EBTCM TP Sensor Sig 12 tan/blk
TCS Spark Retard Request 23 Org/Blk
Only these 2 wires going to the Electronic Brake/Traction control module.

Conn B doesn't show any 12 or 23
Conn C lists 23 Map sensor in Lt grn
Conn D doesn't list any 12 or 23

If that helps any

Ta
Mitch