Did I lose my ECM? 03 Yukon dead in the water

[Elmerwood]

@TJ Baker thanks for the info. I checked my OBD2 port and pin 16 had 12V, pin 4 & 5 had continuity between each other and individually to a ground, pin 2 reAD 10.58 volts both times I checked it which seems odd when checked against your video.

 

[Elmerwood]

Tonight I tried videos I've seen "resetting the ECM" by placing the key in the on position for 10 minutes and then to the off position for 10 seconds. This process was repeated multiple times with no change in the vehicle. One thing I did notice is that when I turn the key off after leaving it on for 10 minutes the display would read different numbers each time. One time the display reads 64 the next time it reads 75 And the next time it read a zero on each end of the display. Does that sound familiar to anyone that there's a issue?

 

[BG1988]

10.58vDC !!!?!?


Hint:


check the battery
it's completely dead or flat... or one of the cells went bad

have it load tested



even in your photo it says 9 bolts of electricity ...

BATTERY is bad


it should be reading 12.3-12.5v (when off) and 12.8 to 14.8v ish(when running)from the OBD port..



OBD2 ECM only has 5v(for sensors) or 12volt rails nothing else

 

[Elmerwood]

@BG1988 in that picture of the dash, that was the last time.the vehicle was running and gauges went nuts. The only gauge that was.working was the speedometer, the others pegged to the left.

That was Saturday. I put a brand new batter in on Sunday and has died twice just sitting in the vehicle so I'm assuming I have a parasitic drain since this has all started.

Tonight I put the battery on the charger and got the voltage up to conduct some testing. Those numbers earlier were the readings from the OBD2 port tonight. Pin 2 had 10.58 volts.

My display when I turned the key off tonight was displaying odd numbers.

 

[Elmerwood]

The numbers only appear for a.very short time so I had to take a video to capture them. This one reads 75. Another time it read 64 and one time a zero at each end of the display.

 

[BG1988]

@BG1988 in that picture of the dash, that was the last time.the vehicle was running and gauges went nuts. The only gauge that was.working was the speedometer, the others pegged to the left.

That was Saturday. I put a brand new batter in on Sunday and has died twice just sitting in the vehicle so I'm assuming I have a parasitic drain since this has all started.

Tonight I put the battery on the charger and got the voltage up to conduct some testing. Those numbers earlier were the readings from the OBD2 port tonight. Pin 2 had 10.58 volts.

My display when I turned the key off tonight was displaying odd numbers.

hmm

error code

• GM MAP sensors do not commonly fail
• Due to erratic engine vacuum, other engine performance problems can cause a code 64 to set

75 Service air conditioning let us know if you get any others

check the ECM/BCM fuse maybe even replace them even if it looks ok...



it could be a faulty capacitor on the ECM if this fixes it then it could be that ... pull the ECM and bring it in the house to "warm it up" Do not put it in the oven ... just becareful as the pins get damage easy

 

[TJ Baker]

@TJ Baker thanks for the info. I checked my OBD2 port and pin 16 had 12V, pin 4 & 5 had continuity between each other and individually to a ground, pin 2 reAD 10.58 volts both times I checked it which seems odd when checked against your video.

Under no circumstances should you see a voltage that high on the class 2 serial data bus! That is outside the range of acceptable values. I would guess a wiring harness damaged somewhere or a module gone bad. My first thought would be damaged wiring which could also be causing your parasitic drain. One approach would be to locate the data bus splice comb under the dash and remove the comb, then check each individual wire to see where that 10.5 volts is coming from. This could point you in a direction for locating the trouble area.

 

[TJ Baker]

It sounds like your issue began with the liftgate. I am not as familiar with the Tahoe/Yukon as the smaller cousin, the Trailblazer/Envoy. In those vehicles the wiring from the body to the endgate/liftgate is notorious for wiring damage from years of opening/closing. Often no external signs of the damage can be seen. Big guess here on my part, but if you were having issues with the hatch, and a power wire shorted or heated enough to melt insulation and get crossed up with a data wire in the same bundle you might see the kind of things you are seeing here.

With 10.58 volts on your serial data line there will be absolutely no communications happening. No crank, no start, no nuthin!

 

[Elmerwood]

I think I need to do what this gent wrote up.

https://www.iatn.net/forums/13/54612/class-2-data-bus-shorted

 

[TJ Baker]

I think I need to do what this gent wrote up.

https://www.iatn.net/forums/13/54612/class-2-data-bus-shorted

Yep, that's about what I meant when referencing the splice comb