99 astro 4.3 cam positioning sensor keeps going out

[georgie1]

Hi all,
I have a 99 astro with the 4.3 motor and over 100k miles. I have gone thru 5 cam sensors in the last few months and cant figure out why. I will change it and the same day I get rough idle and the motor doesnt run right. The check engine light comes on and its the sensor again. I was told to replace the distributor but there is really nothing to them but the shaft and the sensor. Im tired of replacing the sensor and need some real help. I went from using autozone sensors to american standard sensors but its still the same. I just replaced one yesterday and right when I started the car it started running rough. I changed the coil thinking it may be surging too much power and killing the sensor but same thing. I checked voltage while the car is on and im getting 12 at the sensor and the ground is grounding. I even wiggled the plug to see if vibration was the issue. Someone told me to use genuine gm sensor but would that really make it work right? The american standard is what my mechanic uses and has said he has never had a problem with them. Please help im at my wits end.

[mkj54]

What is it your calling a cam sensor? (where it it located?, and if it has 12 volts going to it I'm sure it ain't a cam sensor) AFAIK that engine doesn't have a part known by that name. It has a pick-up coil in the distributor that serves that function. I don't mean to be picky, it's just that we need to be clear on what's going on to be of help.

[Big_kid]

Have you checked the distributor drive gear for wear? See page 2 of this thread: viewtopic.php?f=43&t=2380&start=10

Welcome aboard!

[Phantom]

The dist drive gear may be worn , did you clear the trouble code after you replaced the sensor? If the code is still there the vcm will still think that the problem exists and condition the same , even though problem part has been replaced.

[georgie1]

The part in question is the pick up in the distributar. The code which I don't have on hand says cam positioning sensor again which is the pick up in the distributor. The error code is cleared every time a new one is installed. I checked for any play on the rotary trying to wiggle it back and forth but doesn't seem to have any play. Thank you for all the help so far

[georgie1]

sometimes after replacing the sensor the car runs good for the first day if its not driven on the freeway

[Phantom]

The part in question is the pick up in the distributar. The code which I don't have on hand says cam positioning sensor again which is the pick up in the distributor. The error code is cleared every time a new one is installed. I checked for any play on the rotary trying to wiggle it back and forth but doesn't seem to have any play. Thank you for all the help so far

Symptoms can include:
* Hard starting or no start
* Rough running / misfiring
* Loss of engine power
Causes
A code P0340 could mean one or more of the following has happened:
* a wire or connector in the circuit could be grounded/shorted/broken
* the camshaft position sensor may have failed
* the PCM may have failed
* there exists an open circuit
* the crankshaft position sensor may have failed
Possible Solutions
With a P0340 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:
* Visually inspect all the wiring and connectors in the circuit
* Check for continuity in the circuit wiring
* Check the operation (voltage) of the camshaft position sensor
* Replace the camshaft position sensor as required
* Check the crankshaft position circuit as well
* Replace circuit wiring and/or connectors as required
* Diagnose/replace the PCM as required
The pigtail wire that the sensor connects with may have a bad connection. It may be a wire that is bad and not the sensor , 02 sensor , crankshaft sensor signals and any other component in that circuit could be at fault or have a corroded , or loose connection.
Just because the Check Engine light goes out does not necessarily mean that the code is not in the history and VCM may still think that the code problem still exists, that is why repair techs will use their scan tool to clear the codes that were there.

Is this the part you relpaced?

10485432 SENSOR CM/SHF POSN Item # 10

http://www.gmpartsgiant.com/components/ ... 11005.html

[georgie1]

yes the part # 10 is the one that ive been replacing.

[chevy57bert]

Question: Over here, you can`t clear all the vault codes in your vehicle. (18 wheelers)
It has to do with insurance.. / inspection controls. Only the last 2 codes stay in the system.

Is this also in the USA a rule??

[Phantom]

Not that I ever heard of , but things can change , but when it comes to 18 wheelers that is a different game , serious damage can be done when those lose control , so it seems logical there would be regulation on those , on passenger cars though they have always cleared the codes to reset the ECM/VCM because the vehicle would need to go through "X" amount of drives cycles before the vehicle would perform smooth for customer, all the techs that I have asked about this have told me that just replacing the bad component would result in a rough idle and other rough matters until the VCM relearned the new parameters which would require approximately 200 driven miles before the system learned everything and then it would run smoothly, they clear the codes so that they do not have to clear all the memory of the VCM , if they did not , the customer would notice the rough idle and such and think that the shop either did not fix the car or maybe caused another problem resulting in a unhappy customer and loss of a customer . Unhooking the battery cable until the capacitors drain can clear the codes , but it also clears all memory which can in some cases , mostly the newer cars aprox 2000 & up , some maybe a little earlier necessitate a relearn , a home tech may expect this but a paying customer would not , paying customer wants their car running smoothly when they take it home.

[chevy57bert]

Thanks for clearing up..
The codes where cleared, but stay noticed in memory. It has to do with emission controls.

[georgie1]

ok so what yoru saying is that it could be another sensor going out and still sending out the same code. Im in Orange County Calif and want to know should I take it to the dealer or to a auto electric shop or can someone recommend a shop? If so pm me or post here for all to see. Thank you

[Phantom]

Sorry I don't live in Cali,
You have not stated the exact code you are getting , but yes whenever the cam sensor Circuit has a problem it will set the exact same code , the codes are designed to indicate what circuit the problem is in , it seems unlikely that many sensors would go bad in that period of time . I hope you got a warranty , I need to replace mine , just have not had the time yet the light would come and go for awhile and then it stayed on, will do it within a week , I bought a Ac Delco part and it has a 1 year warranty , you may have something else that is amiss that is sending the code , If you know someone who has a good diagnostic skill and OBD 2 scanner they should be able to find out what is wrong , when I say scanner I mean more than a code reader , it will give live data as to where the problem is .

[georgie1]

ok ill take it into the shop my buddy owns and see if he can find the real problem. Thank you all for the help

[rev_les]

I have 237,000 on my '99, and have never changed the CMP.( It does have a new gear on it as of about 50K ago) If you erase codes, you have to take it through the drive cycle process or the PCM reads "not ready" on the emissions machine, and you will fail. I'd take it somewhere where the real-time data can be collected off it, something doesn't seem right. FWIW, the CMP and the distributor pick up are 2 separate parts. Replacing the pick-up coil requires removal of the distributor.