Need help diagnosing cause for low voltage at electrical connector

[CARmelo]

I have a 2002 Hyundai Sonata. The electrical connector for my transmission input speed sensor broke so I cut it off and swapped it using heatshrink and butt connectors with one from the junkyard. Now the readings on it seem to be off.

This is a 3 pin electrical connector. According to my manual, the values should be as follows with the key in the ON position:

Pin 1: +5V
Pin 2 (Ground): Continuity
Pin 3: +12V

Prior to cutting the connector off, I measured the voltage between pin 1 and 2 and saw +5V, close to the battery voltage between pin 3 and 2, and definite continuity between pin 2 & a ground point. However, once I installed the new connector, I measured:

Pin 1 to Pin 2: 5.01V
Pin 3 to Pin 2: 7.01V

With the values like this, I assumed I messed up my wiring for pin 3 so I measured the voltage drop both ahead of and behind the connection that I made but nothing seemed amiss.

I then decided to check the voltage drop between the battery(-) terminal and the pins of the connector. From those tests, I got:

Pin 1 to Battery(-): 0.08mV
Pin 2 to Battery(-): 5.02V
Pin 3 to Battery(-): 12.04V

So now this is where I’m getting really confused. If I’m thinking right, the voltage between the battery(-) terminal and these pins should be exactly the same as it is at the connector. So I don’t get how the voltages for pin 1 & 2 look so wildly different from their values when measuring directly at the connector.

[Apex]

I could be wrong as electrical is still something I have not gotten enough experience in, but it looks like there’s a short between pins 2 and 3.

If I understand correctly your pin 2 to battery negative should have no potential difference, you should read 0v (unless you have a bad ground, which is another possibility now that I think about it) but now read 5v.

Additionally, your potential between pins 2 and 3 is now 7v instead of 12v. 5v + 7v = 12v

Maybe someone else can chime in here to see if I’m on the right track. Do you read a resistance (as opposed to open) between pins 2 and 3?

[CARmelo]

Yes, the resistance is like 5.3kΩ.

[CARmelo]

Oh my gosh, I figured it out. I got the wire designations and colors mixed up!

I decided to actually sit down and take a good hard look at the wiring diagrams a little closer. I noticed that the ground wire listed for the connector wasn’t the color nor the pin I thought it was. So, at that moment it hit me the ground pin IS NOT Pin 2 and I got everything all mixed up somehow when I was writing down what wire was what in my notes.

It should actually be:

Pin 1 (Ground): Continuity
Pin 2: +5V
Pin 3: +12V

Once I did that everything checked out

Pin 2 to Pin 1: 12.04V
Pin 3 to Pin 1: 5.01V

[Apex]

Great! That makes a lot more sense reading your original post now, if your pin 1 was really supposed to be 5v it would be shorted to ground, not sure why I didn’t notice that before. I was really focused on pins 2 and 3 I ignored what you said about pin 1. Glad that isn’t the case!

[CARmelo]

Just noticed I wrote final results down switched. Total bonehead move.

It should be:

Pin 2 to Pin 1: 5.01V
Pin 3 to Pin 1: 12.04V

[Author]

Posts