Electronics Need help wiring something up? Thinking of adding an electrical component to your car? Need help troubleshooting that wiring glitch?

ECM wiring routing

Old 03-16-2019, 04:36 PM
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ECM wiring routing

Hello,

Just a quick question. I've problems with ECM wiring (code 15...) and I think I've traced it to a break somewhere in the wire where the loom plugs into the ECM under the dash. However, I need to pull that part of the loom out so I can inspect it and work on it. I was hoping I'd be able to disconnect it from the ECM and then pull the wires though into the engine bay to work on them without unplugging everything in the engine bay, but I've read this isn't possible - the 'passthrough' connector won't make it into the engine bay.

Is there another way I can access this wiring? Will it pull through into the wheel well, or is my only option to disconnect the entire harness from the engine and pull it through into the passenger compartment? I'd prefer not to do this as it looks rather complicated, and will be fiddly with the risk of breaking connectors etc...

Many thanks for any advice!

ND
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Old 03-19-2019, 10:52 PM
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Re: ECM wiring routing

If you pull the connectors from the ECM, disconnect the ECM harness from the dash harness, remove the clip holding the 'pass thru' block,...... you CAN pull that end of the harness all the way back into the engine bay. You've got to "snake" it thru the body and into the fender-well, then pull it thru a hole at the top of the engine bay frame rail. ( There is a wire-loom clip inside the fender-well opening to hold the harness in place at the top of the fender well. ) This last bit of pulling the harness out is tricky; the pass-thru plug has to be turned / moved into the correct position before it can be pulled thru the body-metal gap and finally into the engine bay. You might have to make a few attempts,... spinning the plug in different directions and then re-trying - before it can be wedged thru the gap,......... but it WILL fit thru.



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Old 03-20-2019, 08:52 AM
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Re: ECM wiring routing

Yep...there's a "horseshoe" shaped clip on the inside, that secures the pass-through via a groove on 3 sides of it. With it removed, that whole block stays with the harness, and goes out through the fender-well. There are a few photos of mine coming out in the link below.

https://www.thirdgen.org/forums/memb...ml#post5902291
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Old 03-20-2019, 09:18 AM
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Re: ECM wiring routing

Thanks guy for the pointers and the photographs - that'll all make it much easier to do now I know what to expect.

It looks like I'll have to jack up the car, get the wheel off and take out the arch liner, but that'll still make it much easier to work on the wiring than trying to solder upside down in the footwell!

I'll try to remember to tell you how I get on, when I finally find the time to do it!

Cheers,

ND
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Old 06-20-2019, 05:27 AM
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Re: ECM wiring routing

Well, I still haven't got round to this!

My plan is to open up the pass-through connector by heating it up with a hair dryer and prising it apart so I can replace the entire wires running from the ECM connector to the temp sensor.

But, what do I do when I put the pass through back together? Is there a recommended silicone for re-filling it? The car never gets driven in the rain and is garaged, and the connector seems to be protected from direct splashing by the fender-well liner... so shall I just stick it back together and not worry about the gunk? I'll probably not clean it off entirely, only enough to pick out the two wires I need, but I have no idea how much I'll have to pick it apart until I get to it!

Cheers,

ND
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Old 06-20-2019, 12:19 PM
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Re: ECM wiring routing

Is there a reason why you would not just splice the wire after the block? Best repair to do that is a bare metal crimp connector y to make the mechanical connection and then solder it to make sure it's a good electrical connection. Seal it with a bit of heat shrink that has some silicone in it to seal it from the weather.
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Old 06-20-2019, 01:43 PM
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Re: ECM wiring routing

My car's been throwing a Code 15 for a while, showing an intermittent short between the coolant temp sensor wires. I think this happened when I had a Code 14 and I was pulling the ECM about and testing pins, but it turned out the new temp sensor was faulty - it's a long story.

Anyway, in moving the ECM about I think I stressed the wires, and possibly caused them to come apart somewhere in the loom between the bulkhead and the ECM connectors. With the ECM resting on the floor the car didn't throw a code, but as soon as I lifted the ECM back into place... the light came back on.

Long story short, I don't know quite where the break in the wires is, so I may as well go to town and replace the whole damn wires from ECM to temp sensor and be done with it. I might solder new connections just after the pass-through block to avoid having to separate out the loom, but I can test for quality of continuity from there and check if the wire's are ok.

Fun times!
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Old 06-20-2019, 05:56 PM
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Re: ECM wiring routing

With the ECM resting on the floor the car didn't throw a code, but as soon as I lifted the ECM back into place... the light came back on
First thing I'd do is remove the ECM from the harness and closely inspect the ECM PINS and the plug terminals. If there's nothing obviously wrong then I'd isolate the circuit (wire) you've got a problem with and probe/test that circuit. If the wire checks out then I'd suspect the ECM or the sensor. Sometimes a bad connection right at the ECM PIN can be obvious,... burnt marks on the PINS or a plug terminal that isn't pushed all the way into the plug for example.

The LAST thing I would ever do is to split that thru-body connector open just to deal with a single wire ( even if it was KNOWN to be bad, and your still not sure if the wire is bad. ) If I had a bad wire in the middle of that connector - and this is just me - I'd drill a single hole thru the plastic and feed the replacement wire thru it,... leaving the rest of the thing fully intact. Solder in a replacement wire in the ECM harness in the area inside the fender well, then feed it thru the hole drilled in the body-connector, and soldered back to the proper circuit on the other side of the body. Put some small loom around the exposed wire inside the fender-well. ( if you start the new wire all the way @ the sensor then you'll have to run it thru the original ECM harness loom or install new loom on the full length of the exposed wire ) SOOOOooooooooooooo much less work and less potential for problems then trying to open up that pass-thru connector !


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Old Yesterday, 05:53 PM
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Re: ECM wiring routing

Hello John,

Thanks for the extensive answer! Sorry for not responding sooner, I've been busy!

The thread where I was with all of this is here: https://www.thirdgen.org/forums/elec...nt-sensor.html

So you can see how I've run through several possibilities before ending up where I am. The only conclusion I can come to is that I have a short in the wires somewhere. Maybe if I'm lucky it'll be obvious when I start to peel off the loom-wrap. I wonder what else I might find...?

The pass-through connector doesn't look that scary, although I can imagine the goop could be a bit of a pain: https://www.thirdgen.org/forums/dfi-...connector.html I'm not sure about drilling through it though!

I'm still not sure why they actually set it up like this with the wires running through goop, rather than form another connector like the C100 on the other side of the car?

I'll be too busy to work on this next weekend too, so I guess it'll be a while before I sort this out. Boo, I miss my V8!

Cheers,

ND
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