ECM riddle

What keeps your car's engine from spinning when you turn the key and the gas gauge sitting at zero? Before you answer empty gas tank or dead battery, you might also want to know that the check engine light does not illuminate when the key is turned on.

Apparently if you've got a V6 Cadillac CTS then the answer is the Bosch ECM.

It appears that the ECM goes to sleep and then does not communicate with the car when the ignition switch is turned on which then will not send a signal to the start relay. If you remove the starter relay and bypass it to crank the engine, as soon as the engine starts to spin the ECM wakes up and begins to function. (2006 Cadillac CTS 3.6L LY7 V6) Does anyone have any idea of the cause of this strange behavior? or what can be done to fix it. It's kind of a pain to have to open the hood and bypass a relay every morning when I leave for work.

Your ECM is like your radio, in that it likely has two sources of power. One that comes on with the ignition key and a second source that is on all the time. Check your fuse(s).

I thought this was going to be more along the lines of, "What is black and white and red all over?" The GRM logo of course!

They call me the Riddler!

You need to find the power supplies and check the voltage to them while cranking. GM has had some astoundingly bad ignition switches over the last couple of decades.

I'll see if I can trace the power source for the ECU when the ignition is turned to the on position. That seems to be the failure. The few things I found in my online search usually consisted of "it must be a bad ECU so change it" and I'm not really satisfied with that. I did use electrical contact cleaner on the ecu plugs and the main plug between the engine harness and the body harness but that didn't help. Once I get it started by jumping across the starter relay I can turn the engine of and restart it with the key, no problem. However, if I turn the car off and let it sit overnight or even a couple of hours then I have to pull the relay and bypass it again to get it to crank.

EastCoastMojo wrote: I thought this was going to be more along the lines of, "What is black and white and red all over?" The GRM logo of course! They call me the Riddler!

I thought it was going to be a riddle about you ECM.