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 26 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.

Apparently, the MAF Pin 4, labeled low reference, is a 5 volt ref line at ECM C1, pin 51 as seen in the skematic below from the Charm website.

Therefore I suspect my main issue is to fix the S111 line that connects the MAF Pin 3, and the ECT and CMP tan low ref lines to the ECM pin 26 (I cut that line to get the engine to start. The incoming line to the ECM which was cut was then grounded to a bolt on the ECM housing) I suspect a bad S111.....

I found the circuit that shows the splice pack 102, gy line that had continuity with my ground line on the MAF pin 4 line. The gy line is a 5 volt ref line at ECM C2, pin 63. The circuit is below for that gy line.  I guess this makes sense if the 5 v ref circuits all have continuity through the EC--therefore the MAF Pin 4 line being a 5 v ref line (labeled low ref for some reason) has continuity with another 5 v ref line like the gy line from the other connector C2 on the ECM.  Note the gy line feeds 5 v to the fuel pressure sensor.

Perhaps this is a good teachable moment about how this MAF operates. It apparently is a digital type that uses frequency changes to measure mass of inflow. It seems to have a 12 v(pin2) and a 5 volt(pin 4) feed and a ground(pin 3), along with the signal lines for mass (pin 5) and IAT (pin 1). The signal lines apparently feed 5 V reference from the ECM. Is there a video, or some explanation on how the sensors work? ( e.g., does the mass sensor use the 12 v line to heat a resistor, and how is the Pin 4 reference of 5 v used?)

It's been 5 days since anyone commented on this. Can someone respond to this and provide some direction? I'm thinking about running a new Low Reference line to the MAF and the CMP sensors, perhaps splice them into another Low Reference Line on the ECM....?

There is a discrepancy between wiring diagrams from the Charm.Li website and the one I paid for on Portal=diagnostic.com (Automotive Electricians Portal). It shows a 5 v reference on MAF pin 4 on the Charm site (PowerManagement/Diagrams/Electrical Diagrams/Engine Diagram5 ). On the Portal-Diagnostic.com site it shows Pin 4 as a Low Reference on C1, Pin 51 of the ECU. Which is correct? I read 5 volts on this pin when the key is on... I copied the Portal-Diagnostic diagram above, and the Charm diagram is also copied above...

I have two images. First is scanner values with the MAF in various modes, key on, engine off·KOEO, and unplugged, and engine on. Next I used an oscilloscope and measured the MAF sensor line, pin 5.

I am also seeing, according to shop key, that pin 4 is 5v.
I don't think this is a frequency generating MAF based on your scope capture and the description of the MAF in shop key as well.

When driving and having the MAF on the scanner, it is near 0 Lbs/hr airflow (coarse scale). The scanner IAT reading seems ok. Are you sure that MAF Pin 4 is not an ECM provided ground or low reference? It seems that both pin 4 and 3 are not providing proper grounds but I get mixed information from different sources.

When I ask AI, or chatGPT is says this:
The Mass Air Flow (MAF) sensor in a 2003 Cadillac CTS (3.2L V6) is generally considered a
digital (frequency-based) sensor, which is characteristic of GM vehicles from that era.

Signal Type: While some analog sensors output a variable voltage (typically 0-5V), the 2003 CTS utilizes a hot-wire style sensor that translates airflow into a frequency output (Hz) that is sent to the Powertrain Control Module (PCM).
Testing: Because it operates on frequency rather than voltage, it is best tested using a scan tool to read live data in grams per second (g/s) or an oscilloscope to monitor the frequency.
Physical Type: The 2003 CTS 3.2L uses a hot-wire MAF sensor usually featuring a 5-pin terminal.

Diagnosis Tip: A properly functioning MAF on this engine should typically read roughly 3.0 grams per second at idle (or roughly 1 gram per second for every liter of engine displacemen

Are you sure that MAF Pin 4 is not an ECM provided ground or low reference?

No, but I am sure that this pin out labels pin 4 as 5v reference, but I have been burned by Snap-On & Shop Key before.


As a matter of fact, if you follow the simplified Mitchell diagram, it shows pin 4 as low ref. 
Again, been burned by Snap-On & Shop Key before...

I would say that as long as you only have one pin of the MAF that measures 5v, then that's the 5v reference. If you had multiple pins that measure 5v, then we would have some detective work to do.

There are definitely some discrepancies which understandably complicate the matter.
It may be worth your money to buy a few days worth of service information from AC delco just to know that you are getting accurate service information.
www.acdelcotds.com/subscriptions

Also, be careful with Chat GPT. It's not all that intelligent in my opinion.
I'm not saying the MAF isn't a digital type sensor, general motors certainly use them, but your scope capture isn't a digital signal and shop key doesn't specifically say that it is or is not.

I found this information online that explains the use of a 5 volt reference feed to the MAF (pin 4 in this case, perhaps)...

A digital GM Mass Airflow (MAF) sensor uses a 12V supply to heat a sensing element and a 5V reference (or internal circuitry) to monitor temperature, translating air cooling effects into a frequency signal (Hz). As air passes, it cools a hot wire, requiring more current to maintain a constant temperature; the sensor converts this current change into a digital frequency proportional to the mass of airflow.
How the Components Work Together:
12V Power Supply: This provides the necessary power to heat the platinum hot-wire element to a set temperature (often
) above the ambient air temperature.
5V Reference/Signal: In many digital GM systems, the sensor uses a 5V reference to power internal logic circuits that monitor the heat, or it produces a 5V-based pulse-width modulated (PWM) or square-wave frequency signal back to the ECM.
Measurement Process (Hot Wire):
The 12V circuit maintains a constant, high temperature on the wire.
Incoming air cools this wire. The rate of cooling depends on the mass of the air (denser/more air = more cooling).
The sensor increases current to the wire to keep the temperature constant.
Digital Output (Frequency): Instead of a 0-5V analog voltage, the sensor's electronics convert the current required to maintain temperature into a digital frequency signal (measured in Hz).
Low Airflow (Idle): Lower frequency (e.g., lower Hz).
High Airflow (Acceleration): Higher frequency (e.g., higher Hz).
The PCM uses this frequency signal to accurately calculate the mass of air entering the engine for fuel injection, often compensating for air temperature via an integrated IAT sensor.