Crankshaft position sensor

jim8923

Hey guys, does anyone know definitely if on a 1999 Buick LeSabre 3800 engine, if you have a bad crankshaft position sensor whether or not it will throw the check engine light. I had a mechanic tell me that it may not throw the check engine light. I know this is an old vehicle, but it only has $105,000 mi on it and this is the problem has been going on for a while. It just randomly stalls. I have read all the previous posts about random stalling. But I could not find if it would or would not throw a check engine light if it is the crankshaft position sensor. Any help would be appreciated and as always thank you for your time

Michaell

Paging @imidazol97 ..... please pick up the white courtesy phone.

oldfarmer50

Possibly not. I’ve had several old cars of that era that had bad crank sensors and none of them threw a CEL.

On the other hand I had a pre-OBD Oldsmobile that would randomly shut off while driving. It would start right back up as soon as you pulled over. It was the computer.

imidazol97

@Jim8923 IT's what you didn't say in your post that helps diagnose that it's may not be the CPS.

The CPS does NOT set an engine light on those cars. That problem drove lots of people nuts. The magnetic field in the sensor deteriorates with age and from the heat. The Hall Effect will quit working USUALLY WHEN THE ENGINE GETS WELL WARMED UP. You didn't mention that symptom connection.

Also you did NOT mention that it takes 10 or 15 minutes sitting and engine cooling off for the thing to start working again and the car to restart. IF car won't restart right away, throwing cold water on the sensor under the edge of the harmonic balancer will cool it down faster and speed restart. Good check to verify it's the CPS. But in your case, no time before restarting, So CPS is down the list.

It is possible for the connector to give trouble that's close to the harmonic balancer where the ICM is under the edge. Something of a fretting effect on the contacts may give a poor connection. Separate, inspect, clean the contacts and reconnect if your mechanic has not already done that.

I'd tend to think the ISC and the connections on the 8 or 10 pins on the plug. Remove, clean, spray, reconnect. The ISC (ignition spark control) is the flat plate under the 3 coils.

There are tests if the engine will not start due to a ICM that you can do on certain leads there because with the engine cranking certain leads should be giving electrical signals from the ICM. But that helps only if the engine does not restart right away and you are set up to test it when the engine won't restart.

If you don't have a buddy with a 3800 that you can remove the coils and swap ICM on the two cars to see if it makes a difference. Also the ICM needs to be against a smooth back with a layer of dielectric for good thermal contact to cool it IIRC.

If you do try pick and pull to get a replacement, Here's a list of vehicles with the same part, from rockauto.com info on the OEM ACDelco part:
BUICK ALLURE 2005-2009
BUICK CENTURY 1993
BUICK LACROSSE 2005-2009
BUICK LESABRE 1992-2005
BUICK LUCERNE 2006-2008
BUICK PARK AVENUE 1991-2005
BUICK REATTA 1991
BUICK REGAL 1990-2004
BUICK RIVIERA 1991-1999
BUICK SKYLARK 1993
CHEVROLET CAMARO 1995-2002
CHEVROLET IMPALA 2000-2005
CHEVROLET LUMINA 1998-1999
CHEVROLET LUMINA APV 1992-1996
CHEVROLET MONTE CARLO 1998-2005
OLDSMOBILE 88 1992-1999
OLDSMOBILE 98 1992-1996
OLDSMOBILE ACHIEVA 1993
OLDSMOBILE CUTLASS CIERA 1993
OLDSMOBILE CUTLASS CRUISER 1993
OLDSMOBILE INTRIGUE 1998-1999
OLDSMOBILE LSS 1996-1999
OLDSMOBILE REGENCY 1997-1998
OLDSMOBILE SILHOUETTE 1992-1995
OLDSMOBILE TORONADO 1991-1992
PONTIAC BONNEVILLE 1992-2005
PONTIAC FIREBIRD 1995-2002
PONTIAC GRAND AM 1993
PONTIAC GRAND PRIX 1997-2008
PONTIAC TRANS SPORT 1992-1995

imidazol97

There are some other random things to check. Does it stall when hitting a bump a certain way. Might be ignition switch (the actual switch, not the key lock cylinder) worn from use and age. Loses contact internally; car dies; restarts.

The battery has some small leads that go to the fender from the black negative. Clean and retighten those at the fender.

The battery has two positive red power cables. Usually something else would turn off if the lead filler piece between them is corroded or deformed and not making good contact, but I guess you would notice the engine losing ignition. Remove and separate those to be sure they are clean and not corroded. Replacement lead fillers are available.

And there's always removing the leads from the Powertrain Control Module and checking contacts, cleaning them, and carefully reconnecting.