Tips for chasing wire harness shorts

SkyGypsy

Member
I just can’t get through a winter mountain tour without some issue. At least this isn’t as bad as last year’s turbo failure.

My van was experiencing what I would describe as a hiccup on acceleration. Finally a check engine light illuminated and a scan revealed code P0180-1. Indicating a failure of the fuel temperature sensor. Essentially, the temperature sensor Is experiencing an intermittent open circuit which causes the fuel rail to open and send the fuel back to the tank significantly reducing the pressure in the rail, thus causing my acceleration hiccups. Luckily it’s not occurring at highway speed’s. Swapping the sensor for a new one did not fix the problem.

I know it’s basic electrical work but if anyone has any tips for finding shorts or opens in the sprinter wiring harness please do share. Thanks.
 
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Deleted member 50714

Guest
A digital multi-meter "DMM" is needed. Then you need to research values like voltage/ohms. Start visually checking wire and connections, particularly, connector pin integrity/corrosion. Check injector wires, known to chaff against adjacent metal fuel lines.

Check battery cable terminals and posts, clean with wire brush battery post-cable-terminal cleaner, regardless of what they look like. Check engine to chasis ground strap.

Locating shorts can be a challenge for even the most experienced Sparky.


Some basics

https://m.youtube.com/watch?v=JFThdbDYL-c
 
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autostaretx

Erratic Member
An all-too-common failure in the T1N is wiring harness damage where it makes a sharp bend behind the fuel filter.
It's held (too tightly) in place against the engine block, and vibration causes the block metal to rub/abrade/squeeze the internal conductors' insulation to the point of exposing the copper and causing shorts.

You can cut the plastic tie-down, and "ease" the bend ... if the symptoms change, you've located the fault.
After that it's either slit open the harness wrapping and fix individual wires, or replace the engine harness.

Example:

WiringHarnessDamagel.jpg

--dick
 

koenb

Active member
Best advice if you are trying to learn and practice spark chasing, study the basics. Having a solid understanding of how voltage, current, and resistance relate and vary between series and parallel circuits is essential to recognizing how you would test circuits with multi-meters. Don't get wrapped up with Watts and the math involved with calculating values. E/ I*R and what not. It's good to know, but when troubleshooting comes up its usually always found by probing for voltage or resistances. Rarely do I use my meters ammeter function.

Becoming proficient at troubleshooting requires being good at hypothesizing how certain faults would cause the symptoms you are observing/measuring. The key to this is having a solid understanding of how the thing/system is supposed to work. Which requires experience and studying diagrams.
 
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billintomahawk

Guest
After the multi meter.
The wiring diagram or circuit in question printed on paper will save your sanity and make notes and rerefrence easy.

Make up two 4 foot jumpers, one red, one black with alligator clips soldered on the ends, an absolute must.

A roll of 3m Super 33+.

A quality made sharp pair of scissors.
They are a tool. Cut the tape.

https://www.amazon.com/Gingher-01-0...ywords=scissors+6+inch&qid=1580353742&sr=8-35

A razor knife and a good supply of blades.

A soldering iron and solder for electronic work.

https://www.acehardware.com/departm...VYRh9Ch2CFw0HEAQYESABEgLvU_D_BwE&gclsrc=aw.ds

Some zip ties.

All in the same box.

bill in tomahawk
 

NBB

Well-known member
An all-too-common failure in the T1N is wiring harness damage where it makes a sharp bend behind the fuel filter.
This might be true, but it’s an anomaly. Also, this sort of failure is more likely to produce a short than an open. The vast majority of open ckt failures are not mid-wire, they are far more often corrosion or a mechanical failure at the connector contact or crimp.

Edit - also, the best way to track this down is to test things by using a needle or sharp probe to penetrate the insulation a little back from the connector. This way the connector is in-situ and the failure mode undisturbed. It also saves time because you’re not unplugging everything.
 
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billintomahawk

Guest
Quote NBB

Edit - also, the best way to track this down is to test things by using a needle or sharp probe to penetrate the insulation a little back from the connector. Quote NBB

You can sharpen the probes on your multimeter or use a safety pin.

bill
 

SkyGypsy

Member
Ok so rattling the wire harness near the fuel filter has caused the issue to go away. I'm thinking about cutting the harness open to check it out. I'm also curious, if I ran fresh wires from the ecm to the sensor, would I install new connectors on both ends of splice in the wires? And if that is the easiest and most effective approach, does it even make sense to open the harness?
 
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Deleted member 50714

Guest
Rattling? MB calls it the "Jiggle test" (see Sprinter 2007 SM, ELECTRICAL SYSTEMS ) Yes, open the harness to, at minimum, perform an inspection.

Not aware of your electrical experience, bone up on soldering splices and heat shrinking. Never use run of the mill electrical tape in a hot engine compartment, tape's glue can't handle the heat and becomes a pesky gooey mess.

If you can find them, you can replace connector pins/terminals but requires special tool to remove pins from connector. An astute mechanic could use jeweler's screw driver but pin extractor tool the tits.
 
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markxengineering

Active member
I'm also curious, if I ran fresh wires from the ecm to the sensor, would I install new connectors on both ends of splice in the wires? And if that is the easiest and most effective approach, does it even make sense to open the harness?
If not replacing the whole harness yet (highly recommended, because they fail frequently according to those who repair sprinters for a living, and this won't be your last problem), I would cut the wire in question a few inches from the ECM and a few inches from the sensor, solder in a new wire, call it done. I can't see the advantage of opening the harness and looking for the problem unless there is difficulty in routing your new wire that would be made significantly easier by replacing a shorter segment of it. In my experience, my fault was only located after having the whole harness mostly out for maneuverability.
 

autostaretx

Erratic Member
If not replacing the whole harness yet (highly recommended, because they fail frequently according to those who repair sprinters for a living, and this won't be your last problem), I would cut the wire in question a few inches from the ECM and a few inches from the sensor, solder in a new wire, call it done. I can't see the advantage of opening the harness and looking for the problem unless there is difficulty in routing your new wire that would be made significantly easier by replacing a shorter segment of it. In my experience, my fault was only located after having the whole harness mostly out for maneuverability.
If you're not going to change out the entire harness, then by all means slice open the harness and *look*.
Your symptoms only suggest "one wire" at fault ... but in the bundle usually multiple wires are being worn. Without looking you're leaving yourself open for more problems.
(such as: why did it report "open"... a break in there is pretty rare, so it could have been confused by shorting to another wire that trigger the wrong fault).

I'd have no problem with the idea of just repairing a few individual wires ... many of them may only need a wrap of suitable tape (friction tape?) or maybe even a dribble of Tool Dip to provide a rubbery coating.

--dick
 

NBB

Well-known member
If you're not going to change out the entire harness, then by all means slice open the harness and *look*.
Yeah - be a pro about it and actually fix the thing. Nothing says "amature gong show" more than popping the hood and seeing a bunch of wire routed around the engine outside the harnesses - I'd just close the hood, turn around and say "no" to that bs. If you have to spend a day exposing things - well, too bad, that's your task.
 

markxengineering

Active member
My suggestion is based on my recent experience- it was very difficult to see the fault without harness removal, because it's buried in a sharp turn with about 50 other wires in a place with minimal access and lighting. In this spot, I think you are as likely to do more damage if you go looking for it, and waste time. The exterior wire is a temporary solution. I don't see anything amateur about it as long as it is replaced later.
 

Midwestdrifter

Engineer In Residence
In aircraft harnesses, we often swap/replace wire pairs. The harnesses are made with extra wires which helps. Sometimes its necessary to run a new wire(s) along the existing bundle. This is done on both a permanent and troubleshooting basis. Its often not feasible, or time efficient to try tracing down damage inside a big bundle. If an external inspection comes back negative, and the harness continues to perform with no shorts in power wires, then its left in place. Digging around trying to find the break or similar is a great way to destroy a bundle/harness.
 
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billintomahawk

Guest
Just a side note on rodent damage/chewed wires.
My harness was destroyed from mid chassis back to the tail lights. There was one slight chew in the main harness in the starter area.

I bought a chunk of used harness from million mile sprinter and very carefully joined 17 wires using a non soldered 'western union splice' along with dialectic grease, high quality heat shrink tubing and Scotch brand super 33 tape. Then I painted all the cloth wiring harness with water based house paint. The critters want the salt in the cloth and on the wire insulation, I'm convinced that's why they eat it. So the paint stops all that.

This is/was a little like surgery and it needs to be clean but I am a retired nurse among other things and good with tape and scissors.

Like MWD says you can make repairs if you use skill and have fair vision. A headlamp helps.
I have 17k miles since the fix.
I travel with rat and mouse spring traps. And peanut butter(for the bastards).

https://sprinter-source.com/forum/showthread.php?t=67781

bill in tomahawk
 
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NBB

Well-known member
That's great, but you haven't even found the problem. Does a hack take less time, sometimes work, and make you feel good that you avoided a much more difficult and crappy job? Of course it does - until the unfixed problem reappears 1000's of miles from home.
 

autostaretx

Erratic Member
There is a paragraph in John Muir's classic book How to keep your Volkswagen Alive for the Compleat Idiot which says, in essence:
There are times when you're going to have to do a string-and-ScotchTape repair to get out of the muck and reach your destination. You promise the car that you'll fix it correctly when you get there.

Whatever you do: Keep Your Promise!
--dick (especially apt when driving VWs in Africa)
p.s. still in print: https://www.amazon.com/Keep-Volkswagen-Alive-Step-Step/dp/1566913101?tag=sprintersou02-20
 

Midwestdrifter

Engineer In Residence
On my old VW vanagon, I would keep of list of temporary repairs, with a follow up date/miles. We do the same with AC maintenance, as many repairs are not permanent. IIRC I passed that same list onto the next owner. It was shorter, but never completely empty...
 

SkyGypsy

Member
That's great, but you haven't even found the problem. Does a hack take less time, sometimes work, and make you feel good that you avoided a much more difficult and crappy job? Of course it does - until the unfixed problem reappears 1000's of miles from home.
Relax bud your not even talking to the OP anymore.

Clearly the harness will have to replaced sometime in the future. The van is in the body shop at the moment so I'll inspect and assess when it comes back.
 

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