P0726 and no visible harness issues

Hey Guys,
I have a 2006 Jetta that just started doing the typical G28 ESS engine speed sensor crankshaft sensor thing. Tach drops to 0, hard to start, lots of lights on the dash including gp and like 3 others. I use a cheapo scan tool to clear the code and it usually comes back within 5 miles.

I can drive it around when it does this with no noticeable performance issues. I haven't tried to drive far this way, just testing it around the neighborhood after some attempt at "fixing" it. The other day I wiggled the wires around the oil cooler and it seemed to help; the car drove with no issue for over 30 minutes. But it's back and now it happens immediately after I clear the code, there is no driving without it anymore.

Today I pulled the battery and airbox, checked the harness everywhere I could reasonably access (didn't dig between the engine and firewall very far), and wiggled the wires around the oil cooler. I didn't see any wear or chafing on the harness, it looked really clean and intact. Grounds are clean.

I'm still having problems, and here is my question:
What should I do next?
I've heard the engine speed sensors rarely fail. Is there a way I can test mine? If that's not it, I may not know what to look for in the harness. I imagine it would be rubbed through the black tape wrap if it were chafed. Is there a spot where the wires get excessive wear that I'm not seeing? I now realize I never tested the battery...would a bad battery do it? I've read that just replacing the whole harness can be easier than looking all over for the problem, but I would hate to do that and not fix it.

Please help! Oh, and if I do need to pull the ESS, how likely is it that I would damage the rear main seal? It looks like the sensor can be removed, but some folks act like it destroys the RMS when you do that. Any truth in that?


Thanks everybody!

You'll probably need an engine harness... but first contact your local dealer with your VIN and see if they are even available still for your particular car. There are several options.

If they have trouble finding what you are looking for (they will), tell them to look at ETKA illustration 971-011 under JEM 2006, position #1 in the illustration.

It will be something like 03G-972-619-XX . There is a mistake for some BRM cars as I found out too.

You can replace just the CKP sensor, it can be tricky to get in there to get at unless you remove the oil filter/cooler stand from the front of the block, but more times than not it is the harness causing all the problems. I've fixed so many goofy problems on BRMs with a new harness, even after I have fixed the car I have tore into the known-bad harness actually LOOKING for a problem and often cannot pin point anything. Often I diagnose them by doing an Ohm check on a particular circuit from the component plug all the way back to the ECU plug. I have had them where I could slightly push or pull the the harness just so and make the DVOM reading jump about.

If you do decide to replace the engine harness, go ahead and get a new coolant flange for the head, as you'll want to take that off to make getting the new harness in MUCH less stressful.

Thanks for the reply!
I will try calling the dealer, but what do you think about the harnesses offered here: https://www.ecstuning.com/Volkswagen-Jetta_V--TDI/Engine/Electrical/Harness/Engine/


What is the hardest part of the harness replacement? Do I need to jack up the car or move the intake or unhook a motor mount or anything? Is there a video or step by step that you are aware of? I hate electronics!



Thanks again!

Nothing wrong with ECS tuning, but they are just ordering a harness from a dealer and selling it to you. I would just go directly to a dealer. That way, THEY are checking with the VIN, and if THEY get the wrong one, returning it will not be a problem for them.

Tedious job but pretty straightforward, only hard part really is you have to cut off the breakaway tamper bolts on the little shield at the ECU. Once you get the wiper arms and cowl out of the way, and remove the little firewall piece, you'll have room to get in there with a chisel and pointed punch or grinder or whatever you like.