I am going to show you an example of a real life issue, and how you can then use this to locate and read the wiring diagram to help you trace faulty wiring.
The car in question is a 2015 Skoda Octavia III
Step 1: The car is scanned and we save this diagnostic session (because car history is important to keep)
Address 10: Park/Steer Assist (J791) Labels:| 5Q0-919-298.clb
Part No SW: 5Q0 919 298 K HW: 5Q0 919 298
Component: PARKHILFE PLA H12 0054
Revision: -------- Serial number: 39491514005930
Coding: 0131061041
Shop #: WSC 73430 790 00063
ASAM Dataset: EV_EPHVA2CAU3700000 003021
ROD: EV_EPHVA2CAU3700000_003.rod
VCID: 47992422FE9974B74E-8012
3 Faults Found:
1079572 - Rear Right Parking Aid Sensors
B1079 14 [009] - Open or Short to Ground
Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 3
Fault Frequency: 2
Reset counter: 98
Mileage: 222684 km
Date: 2021.04.19
Time: 14:36:26
1079316 - Center Rear Right Parking Aid Sensor
B1078 14 [009] - Open or Short to Ground
Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 3
Fault Frequency: 1
Reset counter: 2
Mileage: 222684 km
Date: 2021.04.19
Time: 14:36:26
1080852 - Side Rear Right Parking Aid Sensors
B107E 14 [009] - Open or Short to Ground
Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Status: 00000001
Fault Priority: 3
Fault Frequency: 1
Reset counter: 2
Mileage: 222684 km
Date: 2021.04.19
Time: 14:36:27
Step 2: We need to locate the correct wiring diagram, this is for an Octavia III 2015 car
You will note from the next 2 pictures, that there exists two wiring diagram files from erWin website
Here is the second file...
As you can see from these two documents, the correct file we need to search though is our 1st document, as it "from November 2012" onwards
Step 3: We now need to search the document for a keyword, or we need to use the bookmarks to find the correct section
If you remember our diagnostic log, we can take the name of the control module scanned and use that as our keyword
Address 10: Park/Steer Assist (J791) Labels:| 5Q0-919-298.clb
For our example, we have J791 we can input into a search field on the document
This takes us to this main section
Step 4: We will now need to scan through the next few pages until we find the correct wiring diagram, which will depend on what is fitted to the vehicle
The car in question has 6x rear parking sensors, and some of the pages only show wiring for 4x sensors!
Diagram No. 42 / 6
This shows 2 of the 6 sensors, G203 and G204
Diagram No. 42 / 7
This shows the next pair of 2 sensors, G205 and G206
Diagram No. 42 / 8
This shows final 2 of the 6 sensors, G716 and G717
Step 5: Now the hardest part is tying all 3 wiring diagrams together.
If we start with the basics, along the bottom row, each image has got a line, along with a row of numbers at the bottom, this is what ties one page into another so you can follow the trail of breadcrumbs so to speak.
Diagram No. 42 / 6
Diagram No. 42 / 7
Diagram No. 42 / 8
So if you can imagine printing out all 3x pages, you would have to lay these 3x pages from left to right in a linear fashion.
Step 6a: Now we need to examine and work out in our example, how each of the sensors is connected to the Park/Steer Assist (J791) module
Taking a look at this small section: -
Our module J791 is at the top, it connects towards our sensor via T26b connector (the numerical value = number of connections in the plug)
T26b then connects to T12e 12-pin connector, on left in luggage compartment.
Finally we have T3au that is the small 3-pin plug that connects onto the parking sensor itself
Ok, so that was just one section of the wiring from the control unit J791 to just one sensor
Now if we look at the 3x wires that head down to the sensor, we see on connector T3au/1 (left) and T3au/3 (right) two large black dots, along with a black horizontal line heading off to the right side of the image.
The line coming from connector T3au/1 (left) has a large circled X68 Positive connection (parking aid), in rear bumper wiring harness
This means that the wire coming from T12e/10 towards T3au/1 will have a "splice connection" where the single feed wire is split into two or more cables
The line coming from connector T3au/3 (right) has a large circled 352 Earth connection (parking aid), in rear bumper wiring harness
This means that the wire coming from T12e/10 towards T3au/3 will have a "splice connection" where the single feed wire is split into two or more cables
I will add at the bottom of the thread, what a splice connection looks like in real life
Step 6b: We now need to follow onto the next two pages of the documents to make note of what wires go where.
Here is something that should be obvious, but best to point this out.
The connector T12e is named so as it only has 12 maximum connections
Each of the sensors has 3 wires feeding it
Given that there are 6 sensors in total for this example vehicle, you can multiply 3 wires per sensor, and 6 sensors for a grand total of "18" wires
Last time I checked, 18 wires cannot go into a 12 pin connector
So this is why the little black dots on the wiring diagram and the circled X68 & 352 are important, they represent a splice in the wiring.