golem

I expect this is more of a general question vs model specific hence posting here.

I have a 2009 Malibu LT 2.4L that will not crank. Battery has full charge and all other electronic circuits operate properly. Quick inspection shows there is no voltage to pin 85 at start relay with key in START position. If I manually apply 12v to pin 85 with relay installed the relay gets energized and the starter operates. Applying a OHMS meter to pin 57 at ECU connector and cycling the shifter I get continuity at positions P & N only. This should signify the neutral safety circuit is operating normally. I disconnected the harness at the BCM and ECU and proceeded to continuity test the logic circuit between the two -- Wires tested good. Assume this pretty much narrows it down to the ignition switch circuit and/or BCM. Not being familiar with GM's BCM I didn't want to fry anything so am looking for insight as to proper test procedures at this stage.

Any insight would be much appreciated.

tech2

before we go any further...any theft deterrent lights on in the ipc? If yes, you will need to read the codes with a scan tool that can access the body system. a code reader will not do this.

golem

Really appreciate your interest tech2.

No, no persistent theft deterrent indicators. I do see the security light (next to oil indicator) and it illuminates momentarily with key ON but does go off as expected.

I had use a simple scan tool and, as you stated, it shows no body system category nor does it currently have any engine/emissions codes captured. The battery was disconnected for a period of time while testing so I expect all codes would have been cleared.

cleveland63b

have you checked continuity from terminal 85 on the relay to the ECM?

golem

Appreciate the reply!

Sorry, forgot to mention that one. Yes, that wire from terminal to terminal continuity tested positive.

tech2

a scan tool would be nice to check is the bcm is confirming a start request and signaling the pcm.






cranking, the bcm should see power at connector x4 pin d3 pink wire and less than 5v at x4 pin 56 white wire and should have 5v at x4 pin 62 white/black
if no power at pin d2 check the ign sensor fuse 2 amp in the bcm fuse panel...maybe check the fuse first.

golem

Thanks again tech2!

You trying to test me? ;-) . Have to admit I was paused by that "x4" connector, finally found it at rear of BCM. Then it took me a moment to determine that pins 56 & 62 you referenced are actually at the x2 connector not x4. I remain unable to determine your reference to pin d2 although I can verify the 2a run/crank fuse and voltage tests OK.

Test results:

The following are Key OUT/IN/ACC/ON/START
x4/d3 - 2.5v/2.5v/4v/12v/12v
x2/56 - 0v/12v/0v/4v/3v
x2/62 - 5v/5v/5v/4v/4.25v

tech2

yes, you passed the test.
this is the 4speed trans option, correct?


At this point I think you have done all you can without a scan tool. It would be nice to view bcm, pcm data to confirm the bcm is sending the start request to the pcm. if yes, I would say the pcm is nfg.
if I find further info I will pass it on.

golem

Thanks again for the assistance and your sharing of knowledge tech2!

It's a family member's vehicle and, having not driven it, best I can tell by looking at the shift console (P,R,N,D,I,L) she looks to be 4-speed.

Seems it's ending where I expected it would...one of the modules. If it's not a GM-only scan tool and any OBD2 tool will work there's a slim chance I can get a loaner from Advance Auto. Last time I checked with them though their policy is 90 day return and it seems most people borrowing them keep it for the full period of time hence it's never available.

I'll be sure to update when I finally complete the repair.

*EDIT* -- Just found out OBD2 tools are no longer loaned/rented by any of the usual suspects. It's a shame I can't find anyhere what type of signal (constant, pulse, null) is passed over the logic connection between the BCM and ECU. With this I could possibly use a simple logic tester probe light to determine if, at minimum, a signal is even being sent to the ECU.

golem

If I may indulge, one last question...

Do the BCM or PCM require any initializing prior to swapping with a used unit (matching GM/Delphi #s)? I can acquire a used BCM/PCM pair for less than $100. It would cost twice that just to get the vehicle towed to a shop and have a scan performed. Add to that the cost of parts (+ additional service) and it becomes a chance worth while considering most everything else is ruled out. Can even resell the not needed module to halve the final cost.