I am new to the forum. I have a 1994 Buick Lesabre limited with a 3.8L engine. On a cold start up it has a no start. If you cycle the key all the way to the off position and wait say 10 seconds then turn the key to the on position then crank it, it will start, sometimes runs a little rough other times fine once started.
I have a OTC 4000E scanner and looking at data stream I have noticed something I find odd. While watching the coolant temp when I turn the key to the on position it will either read 300 degrees F and then drop down to the correct temp, and when this occurs the low cooling fan will turn on then the high cooling fan until the temp gets to about 226F then the high turns off and when the temp gets to 208 the low turns off. Even when the engine is a complete cold start.
The other either is if you cycle the key to off and then back on quick, the temp will be way low and not read correct thus causing a overheat condition when the engine is running. The temp while watching data when this occurs is around 88 degrees F and will slowly increase but not reading correct because the engine is already warmed up. I have ohmed and voltage dropped and voltage test the connecter on the senor and on the pcm. they check out fine. Wondering if the pcm is glitchy.
The sensor readings will do this both cold and hot with the same style key turn as above, but the car will start fine when warmed up regardless of the coolant temp readings.
Things I have done is replace the coolant temp sensor... same result.
checked and cleaned the grounds under the hood.

does have history codes that reoccur as history codes only. Have cleared and they return
P0118 coolant sensor high temp
p0705 transmission range switch <- haven't checked this code out yet
ANY help input other checks is greatly needed
Thanks
Byron

If you have installed a good temp sensor, then you will need to ohm it cold, with the harness disconnected, reconnect, and then you will have to disconnect the harness connectors to the PCM(when you do all this , do not have the key in the ignition, and the neg bat terminal should be disconnected).....now you will have to ohm the two wire circuit coming into the PCM from the coolant sensor......the reading you get, should be the same as at the sensor......if it is, start moving wire harnesses around to see if the the reading changes....if it doesn't, it looks like a PCM problem....

You may find, when you remove the air box to access the PCM, that there might be a rodent nest in there and that insulation to the wire harness has been eaten, causing false readings....

Ok Thanks, I will review the ohms readings the way you said. The PCM on this car is on the passenger side under the dash.
Just curious if anyone has ever seen this issue with there scan tool?
Also I am thinking there is more then one problem with the car. I could have a fuel problem as well with the hard start when cold as I have been reading here on the forum.
Thanks again for the advice, Ill let you know


Byron

Just a update on the ohm test. Everything checks out with it. I also found a diagnostic flow chart for the ect sensor and testing it. disconnect the 2 pin connector from the sensor, jumper the signal wire to the return wire and see if the coolant temp goes to 266F or above while watching the scan tool. It only slowly started to rise for temp. So failed that part. Next test step was to short the 5 volt signal wire to ground and the temp should spike to above 266, again it didn't. While doing this I did shake wiggle the wires and nothing. So both parts failed, replace pcm. But after awhile with playing with these tests a few times I could get it intermittently go to 266 degrees. But not every time. I went back and checked my grounds on the engine and fenders and ohmed those out again just to make sure and they all were good.
My next question is Can anyone give me any details on a pcm, what to look out for. Should I get the numbers off mine and list it. Does anyone have one for sale here.
Byron

The PCM I have #16183247 BHDU.


Will any pcm with the 16183247 number work as long as I swap the prom?
Or does it have to have the full numbers and letters 16183247 BHDU for it to work.

You should be able to swap the PROM and be fine.

This one is exactly the same numbers but it looks rough on the case as long as it works its ok for me. 94 95 Oldsmobile 3 8L ECM 16183247 16194774 Bhdu Box 10920 See Item | eBay
This one has a one year warranty both about the same price is on better then the other?. GM 1994 1995 Engine Computer ECM ECU PCM 16183247 | eBay


Thanks Mike for your help

I'd go with the 2nd one.

Ordered it, Ill let you know when it gets here. West coast to East coast shipping.

New/used PCM came today, Put it in and the car runs great!
Thanks again for the tips and help