Only getting 3v to a 12v pin on PCM. Any suggestions?
 

Hello all,

I am brand new to this forum and fairly new to Chevrolet. I have a 1998 Blazer that seem to have the following electrical issues

-Temperature and Fuel Gauge Inoperable
-Low fuel light constantly on
-Overhead display (temperature,compass, fuel economy, etc) not working
-ABS light contiuously lit
-Check engine light always on
-No power to 4wd selector


Partial Solution:

I found that pin #13 on the Black connector of the PCM (Brown wire) is only getting 3v when it should be getting full power. I have checked and replaced all fuses and checked all relays but all are functional. If I put 12v of power to the #13 pin then everything (gauge cluster, 4wd, overhead display) works just fine. When I take the 12v power away from the PCM the gauge cluster will continue to operate as long as the vehicle is running, but it defaults back to its inoperable state once it is shut down. The 4WD gear selector display stops functioning as soon as I take the 12v away.

I am trying to figure out if this is a problem with the PCM or is there some other component that is causing the low voltage to pin #13. I am not finding any indication of an open circuit, but I am not sure if there is a bad ground in a wire or circuit that supports that part of the PCM.

Would it be possible to install a jumper to the brown wire at pin #13 that will provide 12v when needed (when the ignition is in the run position) without damaging the PCM? When I have applied power to it during the diagnostic testing I did not notice any negative effects but the power was only supplied for a few minutes at a time.

I hope that I have provided enough information to get some good initial responses and I thank everyone in advance for their input.

As you are aware, that circuit is feeding power to the pcm not the pcm supplying power.


pull the 4wd fuse to isolate the circuit and read what voltage you get on the power side of the fuse holder with the key in the run position. if its 3volts on that side of the fuse, then the problem is not the ecm .


the power feed to the 4wd fuse is fed by the ignition switch connector c211 pin c6 orange wire.

Thank you for your the information. I did not know where to start with this. I will test these suggestions in the morning and post my findings. So, I guess it is possible that it could be the ignition switch causing these issues as well?

yep. I suspect there is high resistance in the power circuit causing a 9volt drop in voltage.

I want to start by saying that I misspoke when saying that pin #13 was receiving 3V; I meant to say that it was receiving .03V, or a virtually open circuit.

I tested the ignition switch to the 4WD fuse and the ignition is outputting 12v and the 4WD fuse is recieveing the same voltage. Would that disqualify the ignition as the possible issue. I have been trying to find a wiring diagram that can tell me where the pin #13 (brown wire) on the black plug of the PCM runs, but I cannot seem to locate anything. I figured that a diagram could help me trace the wire to an open part of the circuit or a failed component.

are you getting voltage on the pcm c4 connector pins 19 black/white wire and 23 grey/black wire? they are fed from the same splice pack that supplies pin 13? If no power to all 3 pins I would check at splice pack 200.


its location is: Strapped to the body harness in the center front of dash area. Try to follow the wiring harness out of the I/p fuse panel to the center front of the dash.