hello, my wife's 04 Gr Cherokee randomly turns off , no shudder just instantly off. with a code reader there are no codes. sometimes restarts . I tried what I read in an other thread I put the key on, pumped the gas 3 times and it started right up. where do I go from here? Dave

 

The two most common issues that cause a no warning shut down are a faulty crank position sensor or a defective powertrain control module, either of those can fail without the PCM storing a code.

 

Your jeep shows the typical symptoms of a failing crank sensor. When mine started this, sometimes it would start back up BY ITSELF if I was still rolling! It will only set a code AFTER it totally fails. The best favor you can do for yourself is buy a genuine Mopar sensor. The quality of aftermarket ones suck! Yes they work, but not for long. The CPS is a hall-effect magnetic switch that reads notches in the flexplate to determine when to fire the spark plugs. Mopar sensors use a neodymium magnet where aftermarket one usually don't. My original one lasted over 200K miles before it failed. It's a $50 part whereas the PCM will cost over $200 and new ones don't exist. Only remans are available as far as I know.

To check aftermarket ones, see if they will pick up a screwdriver. A Mopar one will.

 

. I thought the P0320 code was for the crank sensor. But it can fail or be failing and show no code?

 

P0320 is the code for the total loss of signal from the crank sensor, meaning the PCM isn't seeing it at all. If it's intermittent, it won't throw a code.

 

It takes a crank with no start symptom to set a hard OBDII code, PCM doesn't sense any engine rotation.

An OEM level scan tool will store and graph the history of crank sensor faults on a test run during intermittent periods of sensor failure when one acts up and causes a loss of power or shut down and restart on it's own but those don't set a hard code.

My Autel system I use for module programming has a few options for graphing these types of issues when they come up, what I like most about using it to graph live data is you can select a line chart and it will stream a data line while it monitors the CPS and automatically changes the color of the data line when the sensor faults and resumes sending data back to the PCM.

Think blue data line with red segments overlayed on it every time the sensor isn't working properly.

 

did a scan with a genesis today and a code po320 came up. Dave