Help with E40 LS2 PPEI protocol ? Need to talk to the PCM/ECM through a terminal.

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August 27th, 2010
carl0s

Help with E40 LS2 PPEI protocol ? Need to talk to the PCM/ECM through a terminal.

Hi. I wonder if someone can help. I want to send some normal (non-OBD) commands to my E40 PCM. I don't have the PIM or BCM, but I want to trigger A/C Request/On, which normally goes from the BCM to the PIM via GM-UART/Class-2 over SW-CAN, and the PIM then sends the command to the PCM via high-speed GMLAN, in 500kbps CAN frames.

So, I have my ELM327 interface, and I also have GMW8762 which lists the PPEI protocol frame specification. I am doing my testing by trying to get the Engine Cooling Fan to kick in, (because I don't have any AC hardware hooked up yet), which should be frame ID $3f1 or $3f9, so I am setting the header ID to that, and sending what I think is the correct data packet, but I get nothing back.

When I watch the bus (AT MA on the ELM327), I see all sorts going on, and I can see that the throttle position is coming through like this:
110 00 00 00 00 00 25 00 00

(that's ID 110, because I have the unit set to display headers).

The problem is that this ID does not tally with what's in GMW8762 at all. Throttle position should be in frame $3D1, not $110.

Can anybody help me, maybe shed some light?

My plan for the weekend is to splice in somewhere behind the OBDII connector and watch how EFILive sends the "Cooling Fan 2" command, but I suspect those commands are different, more diagnostics commands than PPEI request type commands.
August 27th, 2010
carl0s

I made some progress today. I can see that EFI Live is using OBD-II mode AE to 'Request Device control'.

This means I can fire up the cooling fans, and activate the AC compressor relay using OBD-II, but I'm not sure if 'activate AC compressor relay' is anything like 'request AC on'. I don't think it is.

So I am successfully talking OBDII over CAN, but that's not quite what I want. I want to talk PPEI over CAN.
August 27th, 2010
joecar

AC request is an input to the PCM... the PCM then has logic to decide whether to activate the AC compressor and the coolant fans.
August 27th, 2010
carl0s

Not on the E40 LS2. The PCM has all the logic, and the pressure sensor input, relay control output, but no request input (hence my mission!). Request goes to BCM, which sends to PCM, through PIM/Gateway, all using GMLAN/CAN stuff.
August 27th, 2010
joecar

Ah, I see, request is via LAN.
August 27th, 2010
Blacky

Quote:

Originally Posted by carl0s

I made some progress today. I can see that EFI Live is using OBD-II mode AE to 'Request Device control'.

This means I can fire up the cooling fans, and activate the AC compressor relay using OBD-II, but I'm not sure if 'activate AC compressor relay' is anything like 'request AC on'. I don't think it is.

So I am successfully talking OBDII over CAN, but that's not quite what I want. I want to talk PPEI over CAN.

What EFILive (and similar diagnostic tools such as GM's Tech2) send is not really what you want to be doing in non-diagnostic mode. EFILive uses what are known as DVT (Dynamic Vehicle Testing) messages. Most of the DVT messages have enablers and limits that restrict them from overriding the controller when certain conditions are met or not met. Such as wheel speed may need to be 0 or brake may need to be applied etc. The DVT messages are not useful for using while driving or operating the vehicle in a non-test, non-diagnostic capacity.

As for what the correct messages are that you need to broadcast on the CAN bus, I'm sorry but I've really got no idea.

Regards
Paul
August 28th, 2010
carl0s

Quote:

Originally Posted by Blacky

What EFILive (and similar diagnostic tools such as GM's Tech2) send is not really what you want to be doing in non-diagnostic mode. EFILive uses what are known as DVT (Dynamic Vehicle Testing) messages. Most of the DVT messages have enablers and limits that restrict them from overriding the controller when certain conditions are met or not met. Such as wheel speed may need to be 0 or brake may need to be applied etc. The DVT messages are not useful for using while driving or operating the vehicle in a non-test, non-diagnostic capacity.

As for what the correct messages are that you need to broadcast on the CAN bus, I'm sorry but I've really got no idea.

Regards
Paul

Thanks Paul. I had started to think that this was the case. If only I had a full car to monitor the bus of. Oh well nevermind!

I would buy a BCM and PIM off eBay, but from what I gather it's necessary to use a Tech-2 to pair a BCM to a PCM, so an eBay BCM would be useless to me anyway.
Thanks for taking the time to explain the DVT thing to me.

cheers,
Carl