terminate can bus without an e38/ecm present

[whypave]

Does anyone have a way to terminate a can bus to get EFI live to connect to a T43 via the OBDII port without an ECM present? I know you can do it if you have an E38 on a bench harness. but I have a vehicle with a Mast M90 ecm controlling a T43. I may have to purchase an E38 for programming but I'd like to find a way to just use the OBDII connector Mast supplies without an E38 to terminate the can bus.

I realize this is a long shot since 99% of the people on here have a GM ecm to go with their T43 but perhaps the folks who tune these for others have ways of doing it.

Thanks!

[gmh308]

Does anyone have a way to terminate a can bus to get EFI live to connect to a T43 via the OBDII port without an ECM present? I know you can do it if you have an E38 on a bench harness. but I have a vehicle with a Mast M90 ecm controlling a T43. I may have to purchase an E38 for programming but I'd like to find a way to just use the OBDII connector Mast supplies without an E38 to terminate the can bus.

I realize this is a long shot since 99% of the people on here have a GM ecm to go with their T43 but perhaps the folks who tune these for others have ways of doing it.

Thanks!

Normally a 120ohm resistor in the ECM CAN connectors will do it. It should connect with the M90 on the bus anyway as it runs a 120 ohm termination resistor internally. Odd if it doesnt connect.

[whypave]

Thank you for the information. Just to clarify when I say there isn't an ECM present I mean a GM e38 or other GM ecm. The Mast ecm is hooked up and running when I am trying to get this to work. The ignition switch is on but the engine isn't running. I hear the fuel pump fire up and the CEL light comes on due to no oil pressure (its not running When I hook up the flashscan 2 to the OBDII port it starts up and is getting 12 volt power on pin 16 and ground on pins 4 and 5. But when I tried to read the VIN or try to read trouble codes I get a no vehicle connected error and I get similar errors from the EFIlive software if I hook my laptop to the flashscan 2.

However when I use my laptop and the same flashscan 2 connected to a bench harness ECM plugged right to the transmission at Corvettes of Westchester we can program the transmission just fine.

So your understanding is that the Mast ECM has a 120ohm resistor to terminate the CAN bus? My next step was going to be to continuity test the high and low can bus wires from the obdII port all the way to the wiring harness on the transmission. the transmission shifts based on signals from the Mast ECM so I believe the high and low can bus wires from the ECM to the transmission are working but there could be a problem from the OBDII can bus wires to the ECM. In the mean time I am searching for an e38 ECM I can make a bench harness with.

THANK YOU!

[gmh308]

Thank you for the information. Just to clarify when I say there isn't an ECM present I mean a GM e38 or other GM ecm. The Mast ecm is hooked up and running when I am trying to get this to work. The ignition switch is on but the engine isn't running. I hear the fuel pump fire up and the CEL light comes on due to no oil pressure (its not running When I hook up the flashscan 2 to the OBDII port it starts up and is getting 12 volt power on pin 16 and ground on pins 4 and 5. But when I tried to read the VIN or try to read trouble codes I get a no vehicle connected error and I get similar errors from the EFIlive software if I hook my laptop to the flashscan 2.

However when I use my laptop and the same flashscan 2 connected to a bench harness ECM plugged right to the transmission at Corvettes of Westchester we can program the transmission just fine.

So your understanding is that the Mast ECM has a 120ohm resistor to terminate the CAN bus? My next step was going to be to continuity test the high and low can bus wires from the obdII port all the way to the wiring harness on the transmission. the transmission shifts based on signals from the Mast ECM so I believe the high and low can bus wires from the ECM to the transmission are working but there could be a problem from the OBDII can bus wires to the ECM. In the mean time I am searching for an e38 ECM I can make a bench harness with.

THANK YOU!

GMLAN termination spec is 120 Ohm, or maybe its a Bosch spec. For M90 to talk to T43 the termination impedance should be the same for a balanced and efficient transfer of data.

Did you manually select the T43 controller to connect to it? Usually a 120 ohm resistor across the CAN helps if the lack of connect is due to physical or link layer errors.

[whypave]

when I am trying through EFI live I have manually selected the T43 with no luck. when we used an e38 bench harness it connected right up and I didn't need to select anything. When I try to connect with just the flashscan II the power from the obdII port turns on the flashscan (no connection to a laptop) but when I try to go into the get VIN info screen or the code scaning screen it says no vehicle detected. I think there is a slow speed mode on the flashscan II. I wonder if I need to try that mode to get it to connect up.

[gmh308]

when I am trying through EFI live I have manually selected the T43 with no luck. when we used an e38 bench harness it connected right up and I didn't need to select anything. When I try to connect with just the flashscan II the power from the obdII port turns on the flashscan (no connection to a laptop) but when I try to go into the get VIN info screen or the code scaning screen it says no vehicle detected. I think there is a slow speed mode on the flashscan II. I wonder if I need to try that mode to get it to connect up.

Have you tried with the MAST harness and no M90?

Have done plenty of T43's on the bench...some seem to need a 120ohm resistor, most dont. Maybe they are just more fussy being a Bosch controller than a GM controller. Even in the car with an E38 on one end, they sometimes glitch i.e. fail part way through on a read or write.

Wierd that you cant connect with an M90 on the CAN. From memory (deducing from other threads) the CAN is "noisy" normally with ECM and TCM spewing messages out and before any heavy stuff is done the controllers need to be told to shut the F up. Maybe the M90 doesnt observe this request...but NFI on whether this has to be done to simply connect up and say hello and read a VIN for example.

Have you tried the 120 ohm resistor in lieu of M90 yet?

[whypave]

I am certainly happy to try connecting to the t43 with the M90 disconnected. I had not tried that before. Sounds like I would need to check if the transmission still gets a +12 signal on the right conductor when the M90 isn't there to turn it on (if that is the right term). When you say a 120ohm resistor in lieu of the M90 it sounds like I need to find the two pins on the M90 harness plug that are the CAN hi and CAN low wires and put a 120ohm resistor across them?

Thank You very much for helping me out. I will try these options tomorrow.

[gmh308]

I am certainly happy to try connecting to the t43 with the M90 disconnected. I had not tried that before. Sounds like I would need to check if the transmission still gets a +12 signal on the right conductor when the M90 isn't there to turn it on (if that is the right term). When you say a 120ohm resistor in lieu of the M90 it sounds like I need to find the two pins on the M90 harness plug that are the CAN hi and CAN low wires and put a 120ohm resistor across them?

Thank You very much for helping me out. I will try these options tomorrow.

You're welcome. Ok if you have not tried that before - M90 disc'd, give it a shot. May work fine without 120R resistor. And yes the resistor needs to go across the CAN terminals on the M90 connector/s.

[whypave]

So I tried to connect to the TCM with the Mast M90 ECM disconnected and that didn't work either. I was finally able to get ahold of someone at Mast today and it turns out they have discovered that their harness which controls the T43 from their ECM had the wiring backwards. They use a resistor across pin 13 and 14 of the TCM to simulate a GM ecm like an e38 and then have the CAN+ and CAN- on pin 10 and 11. The only problem is that the restistor was actually across 10 and 11 and the can + and negative are on pin 13 and 14. So I tried to fix that all tonight but I still cannot connect. now I am wondering if the pin outs are wrong on the other end of their T43 adapter harness as well. I will be back in touch with Mast again in the morning and will keep this thread updated.

[whypave]

So after re-wiring the can wires on the harness I found out from Mast that pins 9 and 12 which "start" the trans aren't turned on unless the engine is running with the M90. this is different than a GM normal application when you can access the TCM with just the ignition on. So I rewired pins 9 and 12 to come on with the ignition and I can now access the TCM just fine. Since my 2007 transmission got damaged I purchased a 2009 transmission with 8k miles on it and I am going to build up that trans with better clutches and welded hubs etc. I was able to read the TCM of that trans as well.

My next task programming wise is that I'd like to install a Corvette 6l80 OS on these 6l80s so that I have the ability to setup TUTD without having a BCM. I understand other people have done this but can I simply load the stock Corvette tune from say HoldenCrazy's web site to get a Corvette OS on the TCM or is it more involved than that? I think I read correctly that for a period of time EFI Live was not allowing full OS flashes on the 6l80/T43 but that with the latest versions of 7.5 that is now possible again?

Thanks gmh308 for all the advice. Its good to know the harness from Mast does include a 120ohm resistor and I have no proved to myself you can program this TCM with out an E38 present. I was told by some tuners that was not possible. Who should I contact to talk to EFI Live about updating the bench harness pdf guide with a T43 bench harness?