View Full Version : Getting codes 18 and 45

07-04-2006, 01:04 PM
I have an intermittant problem with my '89 SC.
Occasionally, the car will start to miss badly. I can see sharp drops in the tach reading when it happens. It misses so badly that it has very little power. It will happen for a few minutes, then it will clear up. Last time, I stopped at a gas station and the problem cleared up entirely when I restarted the car. When this happens, I immediately get codes 18 and 45. Here are the explanations from my Auto-xray scanner:
18: Loss of ignition diagnostic monitor signal to the control module/spark output grounded.
45: Ignition system fault in primary circuit coil 1, 2, 3, or 4.
Engine was rebuilt a few months ago. I installed new cam sensor, crank sensor, and BHJ balancer. DIS module (the thing next to the AC compressor) is about a year old.
Any ideas?

07-04-2006, 02:59 PM
Sounds like a bad dis to me, did you put thermal grease between the dis and the jackshaft bracket? You can bring your dis to certain auto parts stores and they'll test it for you.

07-04-2006, 11:09 PM
I did put in the thermal grease, but the surface is no longer perfectly flat. I had the bracket powder coated and (despite my direction to the contrary) the moron powder coated the machined surface. When I pointed this out, he used a grinder to remove the powder coat. He tried to get it as flat as he could, but it is not as flat as it was.

07-04-2006, 11:12 PM
By the way,
For my GM vehicles. the factory manual has a troubleshooting procedure for each code. I do not see this in the factory manual for the SC. Where do I get these? Do anu of you guys have them for codes 18 and 45?

07-05-2006, 03:18 AM
Is the dis well grounded? Were there any wires cut/damaged during the jackshaft bracket installation? Check carefully. You didint do anything to the harness's did you? My mechanic forgot to tie some wires down one time and they got eaten by a belt.

07-05-2006, 05:09 PM
I did check the wiring. It appears that nothing is mechanically wrong with the wiring.
More news. It seems that the car is fine when it has cooled down. After a certain amount of driving, it will start missing badly. At night, when temperatures are lower, I can drive for about 20 minutes before the misfiroinf occurs. During the day, it only takes about five minutes.

07-05-2006, 05:19 PM
Thats exactly what happened to me, it would sputter and go no-where when it was warm. Putting in a new crank sensor worked for me, though the only code I had was a PIP failure. A Dis is only $20-30 on ebay, it would be an excellent place to start.

07-06-2006, 01:47 PM
I think I found the problem!
I have been driving for about a day and a half with no return of the miss.
It looks like the problem was that the connector to the coil pack was loose.
Almost all of the connectors on my engine wiring harnesses have become brittle with age. Consequently, the little locking tabs have all broken off. This is a particularly bad problem with the connector to the coil pack. The little rubber pieces that make the connector waterproof seem to force the connector apart as things heat up. My temporary solution has been to use tie wraps to hold the connector in place. It seems to work very well.

07-06-2006, 04:11 PM
I read you think you figured it out, but just in case you were interested, code 18: Loss of tach input to ECA;Spout circuit open
18: Spout circuit closed

45: DIS coilpack circuit failure.

Zip ties work good.

07-06-2006, 04:57 PM
"Trust the wire ties, Luke SCywalker"