2011 Chevy Suburban 6.0L 4WD B1440
So I have the above mentioned vehicle. Basically this thing has had several issues that I am working through. Today issue is a code B1440-Power Mode Master Input Circuit Mismatch. So to make a long story short I have a Pico capture of a known good 2014 Chevy Silverado. I know that is 3 years older then the above mentioned vehicle, but it was the only one I could get my hands on at the time, that per the diagram showed the same system used with the same colored wires. So basically what is going on is that BCM is shutting off the 5 volts reference with the key in the “RUN” position for connector 1, pin #4 white wire. I tested at BCM connector 1, pin #4 white wire when the key is turned to the “RUN” position. BCM power mode data PID is showing “accossory” when I should see “Run”. The ignition off run/crank PID is showing “Key out/Acc” status, when I should see “Run”. The connector 1, pin #4 white wire should always have around 5 Volts with the key in the ”RUN” position. Now to confirm this I used the 2014 Silverado as a known good. I also took a bench PSU and powered the connector 1, pin #4 white wire with 5 volts while the key was in the “RUN” position and the ignition off/run/crank PID, went from “key out /acc” to “Run”. The Power mode PID went from accessory to “Run”. All other PID’s are and were showing normal status. The code also went to history. So one would think that okay put a BCM in it. Well I put a used one in at the customer request, but same problem with the same code was present. So I am here asking if anyone knows if there is any other reason for the BCM shutting off the 5 volts before I tell the customer they need to get a new BCM or another used one.
Another note I tested all the voltages and grounds circuits to make sure they could power a light bulb other than the connector 1, pin #14 & #21. They were tested with a normal incandescent test light due to those circuits only having a fused 2 amp limit.
Waveform for 2011(problem vehicle) key position guide.
0s-3.1s is key out.
3.1s-9s is key in ignition cylinder, but key in off position.
9s-14.2s is key in acc position.
14.2s-20.1s is key on.
20.1s-25.3s is key back in acc position.
25.3s-31.4s is key in ignition cylinder, but key off.
31.44s key out ignition cylinder.
Waveform for 2014(known good) key position guide
0-718ms-3s is key out
718ms-3s is key in ignition cylinder, but key in off position
3s-6.3s is key in acc position
6.3s-9.8s is key on.
9.8s-13.1s is key back in acc position
13.1s-16.4s is key in ignition cylinder, but key off
16.4s key out ignition cylinder
Just some thoughts: Are you just trying to solve the B1440 or is there any other symptoms like it doesn't start, or circuits stay powered with key switched off and removed? Is it possible the ignition switch is clocked one tooth off…it's possible to do this, usually the throw from run to crank will feel abnormal. Remember that when a code like this sets, assumptions and substitutions are…
trying to solve the code. no symptoms that I or the customer can tell as of yet. No I don't think its clocked wrong. I get all the right status except Run and crank. What do you mean by common? But no I Don't de pin anything unless I need to or am trying to do something specific. I would have to check but I'm sure I was missing the same 5 volts even with the ignition switch unplugged. I have yet…