2003 Cadillac CTS 3.2 V6 automatic with wiring problems at the MAF and the ECM grounds- P0103 P0118

The car is running ok but there are wiring problems on the mass air flow sensor (MAF) and I am trying to verify the wiring integrity but need:
Pin-out for connector 1 (C1) at the Powertrain Control Module (PCM).  I need the circuit for pin 39 at this connector.  I also need to verify that MAF Pin 4 (labeled low reference on a wiring diagram I saw) is normally at 5 volts as I am measuring, and not supposed to be at ground voltage on this tan wire. 

In 2022 I was on this forum and got this car running but I had to cut (near the PCM) the tan wire to C1, Pin 39 and ground it to the engine block in order for the car to start.  I want to fix the problems with the ground to the MAF and figure out the circuit for the tan wire I cut. 

Attachments:  The second image shows the MAF/IAT sensor first unplugged (low readings), then plugged in and reads just over 4 g/s of air into the engine

Marti 

Here is the topic from when I first got this car running again ( Vegas JAK helped me then):   2003 Cadillac CTS with high voltage on the 5 v reference line2 was created by M arti

I also need to verify that MAF Pin 4 (labeled low reference on a wiring diagram I saw) is normally at 5 volts as I am measuring, and not supposed to be at ground voltage on this tan wire.

LOW REF should be GROUND.

 

 

I measure 5 v on the tan wire at MAF pin4 and get Diag code P0103 high voltage on the MAF signal line. Do I try short to ground ( short to tan pin 3) on pin 4 MAF to see if the code changes to low voltage?

I am assuming that you are checking the voltage with the MAF Sensor connected.

Disconnect the sensor and recheck the voltage. Do you still have 5 volts? If not, I would look for an open in the low ref wire between the sensor connector and the PCM.

Once you verify that pin 4 is not shorted to power, it would be safe to short pin 3 to pin 4.

MAF Pin 4 shows 5V with it plugged in or not. I get 5V when I place the auxiliary ground from the Hook tool on any of the other ground, or low reference lines, or on the chasis ground or battery ground. Always shows 5V when the Key is on, or engine on. When key is off it shows a high resistance to battery ground, about 600ohms

I get 5V when I place the auxiliary ground from the Hook tool on any of the other ground, or low reference lines, or on the chasis ground or battery ground.

If your tool is saying that you have 5 volts on the Negative Battery post, your tool is faulty. 

My tool is a TopDiag P200, similar to the smart hook. It reads battery negative when I touch the tip to the battery negative. It has an aux ground which is used for resistance measurements.

Can you show the PCM connector C1 pinout? I want to trace the low reference lines to C1.

charm.li/Cadillac/2003/CTS%20V6-3.2L%20V...%20Control%20Module/

After measuring at C1 on the PCM I found two things. First, Pin 26 at the PCM is the line I had to cut to get the car to start when I worked a few year ago on it with the moderator that uses a picture of a card (Jack). I cut this line at the PCM and grounded the cut line that goes back to S111.  The other end of the line was left unconnected going back to the PCM.  This circuit goes to the Splice S111 which splices three tan wires going back to the PCM low reference on Pin 26. From S111, It goes to Pin 3 on the MAF and I think the IAT sensor uses this as a ground.

Second, I found on the MAF, Pin 4, tan line is always at 5V, either with MAF plugged in or out. That tan line goes to pin 51 on the PCM which is labeled low reference (measures 5 v at the PCM pin 51). I discovered that it has continuity with a grey line at the splice 102 in the fuse box near the battery. KOEO I measure 5 v at this grey line that somehow has continuity with the MAF pin 4 tan line.  See the pic below and the filled in grey line on SP102 is the particular grey line with continuity on the tan line Pin 4 MAF.