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Discussion Starter · #1 ·
2008 g8,Transmission blew,Installed new transmission.Car wouldn't crank,installed old TCM,Still no crank.?Do i need a reflash?What software is required?

L76 6.0
 

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If that was the R12 (crank relay) contacts that you jumped, then your down to a relay that doesn't energize (when commanded), or the *OK to energize* voltage to that relay, is not being sent out from the ECM. Which means that the ECM did not receive the *everything is correct for the request to start* signal.
 

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It looks like you just need the transmission to send out a closed switch condition (park or neutral position), to the BCM, so it can tell the ECM its OK to crank. You are correct to the point, that within the transmission, there is a device called the *internal mode switch*. It may be part of the TCM portion. But the car needs to see that switch in closed position (which equals park or neutral). Somewhere there is a 16 pin connector to the transmission. Remove it and jump pin #3 to ground. That will simulate a closed switch condition. If the engine cranks, you know what area you have to TS.
 

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Discussion Starter · #8 ·
The cluster shows when its in park or neutral,I would assume the white sensor in the pan that rides the linkage tells it what gear its in.Ill ground pin#3 and see what happens
 

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If you have a scan tool monitor the key position, it should say accy, crank and run, if it shows all those then you know that the ecm is recognized the crank position which should in turn supply power to the relay. I would check at the relay to see if the relay is getting voltage from the ecm to engage. If it is then you might have a bad relay and or ground.
 

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Discussion Starter · #10 ·
Y

If you have a scan tool monitor the key position, it should say accy, crank and run, if it shows all those then you know that the ecm is recognized the crank position which should in turn supply power to the relay. I would check at the relay to see if the relay is getting voltage from the ecm to engage. If it is then you might have a bad relay and or ground.
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When i turn the key,I hear the relays on the side under dash click but no pulse to crank relay.Fuel pump turns on but Im not getting either injector Pulse or spark becsuse it wont fire up.I have ground at the relay but other end is nothing no pulse no power or ground...
 

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If you put in the original Tehcm, then it should be ok... should not need anything to be done to relearn or anything....

where did you get new rebuilt trans?... dealer? friend?... internet?... did you install?..did you get a trans from a g8 or someother car?....
 

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Discussion Starter · #12 ·
Original tcm is installed,brough trans from 08 g8,dropped trans installed trans,wouldnt crank so installed tcm from original trans,still no crank.Just out of ideas.
 

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Its time for a re-write of post #4---- Since the crank relay and fuse combo is located in the underhood fuse box, I don't know how you can hear that relay energize from the cabin. When you said you jumped the contacts (of that crank relay), for sure you removed *it* and jumped pins 30 and 87 ? The ignition key would have to be in the full on position to have any chance of getting the fuel pump to run as well as be able to get the injectors to spit fuel and the coils to fire the spark plugs.
If the engine cranks (with key on), maybe it will lite off. then you pull the jumper out to avoid any possible starter run-on. If your still working on it at this time, keep on a going. I'll look for some more possibilities.


Added info>>> That was relay R12---CRANK RELAY you had been jumpering as well as a positive verification, that the fuse feeding those relay contacts FU8-40A---STRTR is good ?


2nd added info--- If the starter *had* been removed as part of the transmission changeout, was there any chance that you disconnected the *crankshaft position sensor connector* just above it (even by accident) ? As in doing so, might have made it easier to remove the starter. An if you did, maybe *it* did not get re-connected. Without it connected and able to sense crank rotation, no injector or coil spark action will happen.
 
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