Code 18 still exists, now joined by Code 17 - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-18-2012, 01:28 PM   #21
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all those wires are right next to the engine that is normally 200 degrees and higher during the summer especially when you turn it off the temp keeps rising im surprised the wires last as long as they do. so those things are already hot and it wouldnt take much electrically if you had a short or something to melt them. after that they turn into a resistor messing up your signal to the pcm
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Old 03-18-2012, 05:03 PM   #22
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I did a rather messy job of taping up the wires down to the crank sensor; really could have used some help with the job. Today I decided to pull the wire loom up from the cam sensor and after getting the old tape off the loom where it joined into the main loom found that the wires to the cam sensor was in even worst shape. Definitely some current passed through the wires. And of course the heat messed up some of the other wires in the loom.

At one point when I was trying to figure out the stall problem, the engine wouldn't start. I had someone to tell me that a shorted cam sensor could keep one from starting. I was told to unplug the cam sensor connector and see if it would run, and if so, then replace it. It did and I did. I have no idea if the cam sensor was shorted or not as I did not test it, just replaced it.

I took a photo of the cam sensor wires and you can see they got quite hot at some time. Whether this is the cause of my Code 18 or not is yet to be seen; however, these wires do need to be repair. I am actually thinking the ICM harness needs to be replaced if I can find one. The problem is that most salvage yards tend to cut up the harnesses for easy removal of the engine.

If I do have to repair the harness, and that may mean cutting and splicing, what is the best products to use? Do they make a shrink wrap tape that can be used to do a better job? Normally when splicing lines I use shrink wrap tubing but I want to avoid cutting any lines that don't need to be cut. Electrical tape is rather messy and hard to get neat.

I have attached a photo of the wires going to the cam sensor.
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Code 18 still exists, now joined by Code 17-icm_harness.jpg  
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Old 03-18-2012, 05:37 PM   #23
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A search on the net turned up nothing for an ICM harness for my LeSabre. If anyone knows of a source, or can help me to locate one that won't break my bank; which is not much , please let me know. There are not many local resources for me here.
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Old 03-18-2012, 07:11 PM   #24
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do you have a pick a part type yard near you? i tend to have better luck with the ones that arent on the net. all those wires are lookin pretty baked i would spend some effort to get a new harness if at all possible
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Old 03-18-2012, 09:35 PM   #25
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I managed to work the wiring harness out of the car without taking anything more off although I did have to loosen the top metal heater hose and take the nut off the bracket to give enough wiggle room; plus had to take the rest of the wire loom out of the way to work the wires pass the water pump.

There are a couple of salvage yards still left here although most of them shut when the stricter EPA laws came about. I will call around; will have to wait until Tuesday, and see if any have a LeSabre with the wiring harness intact.

I am going to get my brother-in-law to look at the harness tomorrow evening after work. He has rebuilt wiring harnesses for '69 Camaros (He has restored four or five of the things for himself, and has done work for others as well) so has the stuff to work with. It might be we can salvage the wiring harness and replace any wires too far gone. I pulled off all the electrical tape repairs I did; they were crappy jobs.
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Old 03-24-2012, 10:59 PM   #26
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As far as breaks in the wiring, a continuity test showed all wires to be good. I don't know if an ohms test was conducted or not. I tapped up all the wires very carefully. Finished getting everything back in place this evening. Started the car and I knew right away that it was not fixed, the engine sounded rough/not the normal smooth idle. Sure enough, within a minute the CEL lit up. I jump the OBD connector and got Code 18. .

According to the GM Shop Manual:

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With the engine running, the PCM monitors the cam and fuel control references pulses it receives and expects to see six fuel control pulses for each cam pulse. If the sequence of these pulses are not correct for 10 occurrences, DTC 18 will set indicating an intermittent problem with the cam signal or the fuel control signal.

DTC 18 indicates an intermittent fault and may not set immediately or under all conditions. ... A poor connection or fault in the cam sensor CKTs 630, 633, 644, or 645 or a faulty cam sensor may cause the PCM to reinitialize injector sequence when the fault occurs, causing a possible stumble or miss. A poor connection or fault in the fuel control CKT 430, crankshaft position sensor CKTs 643, 644, or 645, the 18X portion of the crank sensor or bent or missing vanes on the harmonic balancer interrupter rings will cause the PCM to stop pulsing the injectors when the fault occurs causing an intermittent stumble or stall.
Since I first got the Code 18 I have changed out both the CAM Sensor and the CRANK sensor; both are AutoZone Duralast sensors. I was sure that when I saw the condition of the wires in the ICM harness that I had found my problem. It could be in the crank sensor connector; to plug it in, the wires have to bend at an angle.

I have tested the ckts described as best I could. There is no easy way to test the crank sensor signals as they go to the ICM unless I used some kind of wire piercing thing.

Please read through the GM Manual excerpt and see if you can give me any advice on how to discover the source of this problem.
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Old 03-25-2012, 09:38 AM   #27
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if you measure continuity on the wires doesnt mean they will pass current properly. wires with only a few strands connected will measure very low resistance but when in the circuit with heat will not pass current as necessary. i still think you should replace the harness.
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Old 03-25-2012, 02:54 PM   #28
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The insulation was off some of the wires but there were no broken strands. When I did the tests before I took the harness off, I did not see any shorts or opens. However, I thought that maybe when the engine was running that vibrations could possibly cause a temp short to occur. Probability wise, it was a long shot. What I really need to do is to examine the 18X pulses to see if any misses while the engine is running. Or for that matter, monitor the cam signal as well to see if it misses. I may try to get one of the cheap interfaces and use a computer for an oscilloscope; I don't really need a lot of bandwidth. I need to get some data so I have an indication of what is occurring.
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Old 03-26-2012, 12:25 AM   #29
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My brother-in-law knows a man that use to be a GM tech; now he is a Honda tech I believe. He said that the contacts on the connectors can sometimes get loose. He wants me to pull the harmonic balancer again, put the old crank sensor on and see if that solves the problem, if not, I am to replace the wiring harness. Maybe I should go ahead and get a new wiring harness before replacing the crank as it is easier to do. If those two things don't solve it, he will bring his big computer up to do a diagnostic on the car.
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Old 03-26-2012, 07:36 AM   #30
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i would just do the harness you tried several different sensors
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