[Jcode68]

My daughters 2003 Liberty recently started stalling out and check engine light was on. Had Advance Auto pull the code and it was A code for Engine Speed Sensor". After doing some Internet research, it seemed to cross reference to a crankshaft position sensor. I replaced the sensor making sure it was seated all the way in and the electrical connection is solid. I disconnected the battery for a few minutes to clear the codes and started it up. After running for a few minutes, it stalled and is now throwing the P0320 code which is No Crank Reference. Where do I go from here? I suppose it could be a defective sensor, but this is pretty unlikely. Help!

[streetglideok]

Always remember, bautozone, advance auto parts, and all those places do not diagnose car problems. All they do is give you the codes stored, and hopefully sell you junk. Crank, and cam sensor codes, especially on chrysler products, can be very misleading. Just a month ago, I had to handle a comeback for one of the guys at work on a dodge with a 4.7L, very similar to our engine, for example. It had a crank sensor code, and the "tech", being the idget he is, shotgun guessed it had to be just that, a bad crank sensor. Didnt even leave the parkinglot before it set the code again. Third trip back, the manager got smart and let me look at it. 5 minutes later, Im showing them live readings from both the cam and crank sensors. Guess what was really bad? Cam sensor... even though it triggered a P0320. Changed out the sensor, backflagged the tech, and got it on the road.

Point of that is, you cant always expect the PCM to tell the truth. Its like a kid, and it tells what it thinks, not what is actual. Could be a bad cam sensor, could be a wiring issue to either sensor, or could be typical junk aftermarket electronics. If you want a reliable crank or cam sensor, buy it right from the dealer. Aftermarket quality control starts at the consumer, not in the factory.

[Jcode68]

Thanks for the response. So could be a cam sensor but to know for sure what it is requires a trip to the dealership and probably a few hundred bucks for them to diagnose. Too bad the PCM doesn't have a higher level of accuracy with the codes it throws. Doesn't help the shadetree guys like myself.

[streetglideok]

It looks at the signals from the ckp and cmp sensors, and when the sync is off, or it sees unsual voltage readings, it sets a code. If the cmp randomly shorts and sends reference voltage on the signal return circuit, or drops to zero volts, then it can confuse the pcm into thinking its a crank(ckp) sensor issue, that its not detecting a crank signal. It can only do so much with what it has. All it takes is a good labscope and 5-10 minutes to pin down which it is, etc. All the codes are designed to do is t tell someone qualified what things are not reading right. If it said what was wrong, there would be no need for us, so hence dont trust what it spills out all the time. Cars are alot more advanced now, and do give alot better info on finding problems then years ago. This stuff is easy, it gets funny when you start to diagnose why your guages stop working, and it turns out its the hvac module causing a network bus failure,lol.

If you think this is bad, pre-obdII stuff can be a real nightmare if you arent in tune to how it all works. GMs would throw map sensor codes all day long whenever they ran bad. 90% of the time they were fine, it was a symptom of the actual problem, not the cause.

[Jcode68]

Well I decided to take the chance that the camshaft position sensor was bad and also took a chance purchasing one from the local parts store since the dealer was closed. Figured worse case, I am out another $25, best case it works and fixes the problem. Guess I got lucky, no CEL and let it run a good 30 minutes and then took for a drive and no problems. Appreciate the responses and advice.
The Audi I just got rid of was actually pretty good with codes, pretty detailed and accurate when a code was thrown it usually nailed down the sensor or component pretty well. Each manufacturer is a little different. I still prefer to work on my 68 Mustang, don't need a computer science degree to troubleshoot and repair on it :-)