'91 Olds 88 - Cam Sensor (Code 41) Problem

Great forum, lots of good information….

I have a ’91 Olds 88 Royale 3.8 V6 with 94k miles….

Here is the situation.

Recently the ECM has been sending a Code 41 (CAM Sensor Circuit) error.

I have used the factory service manual diagnostic chart for Code 41 in an attempt to discover and/or isolate the problem. But without success. Here is what I have done so far…

There are 4 steps on the diagnostic chart. The first checks the voltage at the CAM sensor connector….pins A-B and B-C check out with 10 volts. So the associated circuits (633, 644 and 645) check out with no open shorts, grounds, etc.

Next step checks the voltage at ECM terminal BC5. Terminal BC5 checks out with 10 volts (spec calls for 8 volts or greater) If there is no voltage you “bump” the starter and retest (probably because of the magnet/CAM sensor) If everything checks out you go for step 4.

Start the engine, check the voltage on ECM terminal BC5 (now here is where I’m not quite sure what’s going on…) The voltage checks out at a STEADY 10.5 volts – the voltage does not vary at all. The questions asked in this last step is as follows, “… voltage should be constantly varying around a mid-point of 10.5 volts”

If the answer is “YES” then the problem is a poor ECM connection on BC5 or faulty ECM (so does this mean my ECM is OK since it is not varying??)

If the answer is “NO” (once again does this mean a STEADY voltage is wrong??) then you have a bad CAM sensor connection, sensor or missing camshaft magnet.

The CAM sensor is new, the connection is OK because I used a magnet to duplicate the magnet on the camshaft which changes the voltage from 10 volts to 0 volts and lastly the camshaft magnet is there because you can see it using an inspection mirror.

I have swapped out the ECM and ignition modules – no change. I have tested the wiring harness with a continuity tester and everything seems to checkout (no grds, shorts, etc.)

I used an ODB scanner to capture trouble codes and real-time ECM diagnostic data – everything is within factory specs as outlined in the service manual!!

I reset the ECM and within 2 -3 seconds after startup the Service Engine Soon (SES) light is back on…..Error code is 41 !! I just can’t seem to figure out the problem…

Any help is greatly appreciated.

Your camshaft interruptor magnet was flown out of its plastic cage. Have you hit any big potholes or objects in the road lately?

This is a really, really common problem with this engine. This question gets asked all the time. To make a long story short, search both this forum and the buick lesabre forum for "code 41" and you should come up with lots of posts with details.

Here is the short story: your magnet is clipped into the back of the camshaft sprocket via plastic cage, the cage broke and the magnet was flung somewhere in your engine, probably into the oil pan. To fix you have to remove the front cover of the engine and the timing gear and chain. At this point, you might as well replace said timing gear, chain, damper, and magnet (glue in to avoid another code 41) all at once while you have the engine torn apart.

Edit: Link to a how-to on the easy fix. http://6007.us/cammag.htm
Or...you can cheat and remove the cam sensor, spint the harmonic balancer untill you see the empty hole where the magnet is supposed to be, shave off the "brim" of the magnet, douse with JB weld, and push into hole from the front.

I suggest the former, but the latter has worked before with good results as long as you let the JB dry completely...but at 94k miles you might as well rip the whole thing apart to change the timing gear setup since it generally starts to stretch and go bad between 75k and 125k miles.

Good luck!

Alibi

I pulled the sensor, bumped the crank until I could see the where the magnet was suppose to be.....I saw little plastic snap things and what I thought looked like a magnet.....I will go back and probe the hole in the camshaft sprocket to make sure there is indeed a magnet in the hole....if there is a magnet then I'm back to square one or (heaven forbid) the dealer!! BUT if there is no magnet then I'll do it right and tear the engine down and replace sprockets, chain, etc. and glue in a new magnet....

I'll post back with my findings...

Thanks for the information

I've got the same problem, my '88 v-6 will start every time, but may only run for a second, or maybe 10 minutes. Got a trouble code 41. Am I hearing you can just disconnect the sensor and JB Weld the hole? Or did I misunderstand the post?
Anyway, where the heck is this sensor located on the engine? I can't seem to find any sensors on the upper right of the engine, too much junk there w/the belts/pullys and all.

Thanks, SteveW.

No, you cant just disconnect the sensor. Check the link the last post in this thread that I made.

The sensor itself is easy to replace, but the magnet is what is the PITA to do. It is located in the cam shaft sprocket behind the front cover of the engine. You can see it if you remove the cam sensor and spin the harmonic balancer (and camshaft via timing chain) untill you either see the magnet or a gaping hole with plastic debris in it....

again, check the link.