Code 18 Cam/Crank error

1993 BUICK LESABRE
300,000 MILES
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KIMBERLYW
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Recently I had problems with the car that was finally resolved by replacing the MAF sensor. I used another site to find a solution and was simply told to replace one component after another. I was told to replace the ICU, the cam sensor, and the crank sensor until I finally inspected the MAF and found the heated wire was gone. To recap, I have replaced the coolant sensor, the Ignition module, the cam sensor and the crank sensor. After replacing the MAF the car ran great. No problems until two days ago when I started the car in the morning to allow it to warm up and warm up the interior since it is now cold here; about fifteen minutes idling. When I went to leave the car was running a bit rough and when I got inside noticed the check engine light was on. I turned the engine off and then restarted it. The check engine light was off then came back on. I decided to not drive the car. I check the trouble code by shorting the ADL connector and it flashed code 18. A search of the net said that was a cam/crank error. I checked the connectors and they were tight and I could see no breaks in the wiring where they enter the connector. I removed the cam sensor and checked that the magnet was in place and it is.

So, what causes code 18 and what should I do to correct it? Could the new cam sensor or crank sensor be the source? After completing the repairs I have driven the car about four weeks or so without any problems. I have even allowed the car to idle for fifteen minutes or so twice since the weather turned cold without any check engine lights coming on.
Nov 5, 2011 at 6:52 PM
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RASMATAZ
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Check the sensor's resistances and wiring back to the computer
Nov 5, 2011 at 7:07 PM
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KIMBERLYW
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Where can I find the wiring diagram for this; so I can traced the wires? There are a lot of wires coming in and out of the computer. Where can I get the info on checking the sensors?

Thanks for your answer.
Nov 5, 2011 at 7:47 PM
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RASMATAZ
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No repair manual -you can download online with Mit1 or Alldata for a cheap price
Nov 5, 2011 at 9:47 PM
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KIMBERLYW
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I am purchasing the GM mechanical and electrical service manuals for my car. While I am waiting for them to arrive in the post I have this question. From reading on the net, a code 18 for this car is a mismatch between the cam and the crank sensor signals. This car has over 300,000 miles on the engine that I know of (third owner of the car). I am wondering if the timing could have slipped; if the timing chain could have slip since the chain is worn for sure and the tensioner could be weak. The car was running great until that morning I allowed it to warm.
Nov 7, 2011 at 9:48 PM
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RASMATAZ
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Could be the timing chain has slipped and throwing it out of sequence
Nov 7, 2011 at 10:24 PM
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KIMBERLYW
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How can I check this for timing chain slipped? I have a scan tool on loan that can also capture the data stream. Would that tell me anything. I have checked the cam wiring and that appears to be OK, the ground terminal was making ground. Checking the crank wires will be harder and will do that tomorrow. I know the timing chain and gear needs to be replace in this engine but was hoping to wait until Spring to do that job.
Nov 8, 2011 at 1:44 AM
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KIMBERLYW
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I checked all the wiring and they check OK. I also did some voltage tests for the cam and fuel sensor at the PCM connector. Both were at 5 volts as per specs. I rotated the crank and the cam voltage would go from 5 volts to 0 volts, so the cam sensor is working. Could not check the crank sensor output but the car will crank. Could be there is a broken or bent vane on the 18X, but I don't see how that could happen sitting in the driveway warming up. I put everything back together and the car cranked but ran rough. Smoothed out some after it warmed a bit (could be the PCM recalibrating). Engine runs rough. No codes reported or stored but the engine is not idling correctly. Checked the coil packs and the secondary ohms reading on all coils was around 10K ohms (cheap meter); all gave the same reading. I connected a cornwell scan tool and captured the datastream. I can provide information from that if you can tell me what data you need to help me. I did see that the engine is running lean according to the scan tool. This is my only car so it needs to be running again. It ran great after the repairs mentioned above and just happened one morning while warming up.
Nov 19, 2011 at 8:35 PM
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RASMATAZ
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Clean out the idle air control and EGR valve also check the actual fuel pressure
Nov 19, 2011 at 8:39 PM
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KIMBERLYW
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The EGR valve is clean, I did that when I had the previous trouble. Fuel pressure was checked during the previous problem and was within specs. The fuel filter has not been replaced in several years, so I could do that. Easy enough to do a new fuel pressure check. Will check the IAC.
Nov 19, 2011 at 10:20 PM
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RASMATAZ
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When you do fuel pressure checks-you do it with and without the fuel filter same goes to the fuel pressure regulator w and w/o the regulator to be accurate atleast this is my way on troubleshooting the fuel system
Nov 19, 2011 at 11:01 PM
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KIMBERLYW
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Here is a data stream capture using a Cornwell 3499

LT Fuel Trim: 128
LT Fuel TR CL: 5
Evap Solenoid: off
EGR Sol all of them off
KS Counter: 1
Exhaust O2: Lean
IAC Position: 140
Idle Req RPM: 1288
ST Fuel Trim: 128
Knock RET: 0
Loop Status: OPEN
MAF (sr/S): 3708
IAT (degrees F): 53
O2S (mV): 466
O2S CROSSCNTS: 54
PROM ID: 1284
QUAD DRIVER 1: OK
QUAD DRIVER 2: OK
Spark Adv: (degrees): 23
Nov 22, 2011 at 7:19 PM
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KIMBERLYW
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This problem is still not resolved. I have done all the checks listed in the GM Shop manual. The key to solving my problem is removing the Code 18. Fuel pressure problems don't case a code 18 to be set. The ERG valve does not cause a code 18 to be set. The code 18 is going to keep the engine running in an open loop mode, so of course the engine is going to idle like crap.

Now, I have swapped out both new cam and crank sensors. I went into the engine and checked the timing gears and chain, the timing had not jumped but a new timing set and damper were installed. The harmonic balancer vanes are all in place, none of them are bent, and I even cleaned them in case contamination was interfering with the sensor. I checked all the wiring and even replaced the computer PCM, with a reman one. I can see nothing wrong here. I even put the old ICM back on just in case the new one was defective, no change.

Something has to be causing this code 18, is sets only seconds after starting the engine. I will be happy to donate or pay for a solution if someone can help me.
Mar 16, 2012 at 8:20 PM
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RASMATAZ
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Check and test the coolant temperature sensor resistances Hot and Cold-

DTC 18 Cam/Crank Error
Mar 17, 2012 at 12:04 AM