The problem isn't always where you think it is

Kevin Owner/Technician New York Posted   Latest  
Case Study
2006 Volvo XC90 2.5T 2.5L (59 B5254T2) 4-spd (4T65-AWD)
Ldp Does Not Operate
Failed Emissions Test

We have a Volvo XC90 with a brand new customer installed LDP yet it is throwing codes indicating that it isn't working. A check at the ldp, which is in front of the spare tire in the rear of the vehicle indicates that there is no 12v present as well as no commanded signal either. A check of fuse #15 in the engine compartment fuse panel reveils a 10a fuse where there should be a 15a, but power is present. After installing the correct fuse and again confirming voltage across the fuse, I verified that voltage was present from the fuse panel into the main harness. A quick search indicated that the wiring harness ran along the passenger sill area and that pinched or corroded wires were common. 

After removing the rear seat and necessary trim, I was able to verify that indeed no voltage was present their either on either the commanded or supply wires. A check of the schematic that I had used showed no weld points or splices as well as no connectors, and indeed none were visible. One more sill panel off near the dash and yet still no signal. Hrmm.

A check of the factory schematics (should have done this first) revieled that there were indeed two connectors in this circuit, one in the dash and one below and behind where the driver would rest their left foot. One more sill plate off and some soggy carpet later, what was staring me in the eyes but a pretty blue section of wiring harness and a rotted 4 wire square connector ! Yippeeeeeee ! Apparently, some engineer decided that there was too much wire designated for this task, so he routed it down the driver's side sill plate before returning back up into the dash and across to the passenger side to run down that sill and ultimately to the ldp. Some splicing and removal of the pretty blue goo from harness, and everyone is happy again.

Why did I write this? A couple reasons I guess. If the interactive schematic that you are using doesn't show splices or connectors or designate their location accurately, take the initiative to double check their accuracy. Also, don't estimate that because something appears to be in one location that the rest of the circuit didn't take a detour along the way. Circuits can work with the incorrect fuse in place, but should never be left in that condition, and if you have power in the origin or the circuit but not at the component, split the difference and see if it is present there so that you don't waste time chasing the wrong half of the circuit. Hope this helps someone where Google and a non oe schematic led them astray . Thanks,


Ryan Owner/Technician
New Jersey
Ryan Default

Kevin, good post! what system did you get the first diagram from?

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Angel Technician
Angel Default

Great post Kevin, thanks for sharing. We have aftermarket wiring diagrams and service information, they’re great until they’re not. Having OEM service information is the way to go. & yes even when it doesn’t seem possible, an engineer will make It possible. Great find and thanks for sharing

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