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24Jul/1122

Troubleshooting: 1998 Jeep Grand Cherokee (ZJ) Doesn’t Start – Cranks, No Fuel, No Spark

This has been one of the most frustrating repairs we have come across. One day the Jeep just plain refused to start anymore. We have had prolonged starting times for a while now where we will let fuel pump prime at least twice before it would start, but it would always start. Nothing really precluded the no start condition, we just turned it off one day and it didn't want to start again. The symptoms don't really point to any particular component (other than the PCM) and without some fancy tools, you'll do exactly what we did - replace the PCM... and it won't fix anything. So we took out our fancy tool, looked up some diagnostic diagrams on alldatadiy.com, and got to work.

A few things to check for right away to see if you're having the same issue we were:

  • Check to see if the fuel pump runs during cranking - ours didn't
  • Check for spark during cranking - we didn't have any
  • Check to see if your check engine light is on (ours WASN'T)
  • Check your voltage and fuel gauges with the ignition on - ours didn't register anything
  • Check to see if your low fuel light is on - our was

  • Fancy tool time - we hooked up the Genisys EVO to the data link connecter (located under the steering wheel):

    We first tried to connect to the PCM computer to view the Datastream (and check codes) - whatever it would tell us:

    Aaaaand it said it didn't want to talk to us:

    Then we moved on to the BUS monitor to see if the bus was up and what computers we could talk to:

    Looks like the Body computer (BCM) is willing to talk to us:

    Now, we see the bus is up, the PCM appears to be down - so we replaced the PCM. Unfortunately replacing the PCM did absolutely nothing for us other than lighten our wallets. At this point, we did some digging on AllDataDiy for an appropriate troubleshooting test to figure out what on earth was going on. While I can't re-publish their content due to the ToS agreement, I can tell you how we arrived at our final solution.

    We started by testing the Throttle Position Sensor voltages:

    Pin 3 should be above 4 volts:

    Since it was under 4 volts, we unplugged the Camshaft Position Sensor (connector locations below - this is the passenger side of the engine compartment):

    And checked again - still under 4 volts:

    Then we unplugged the Crankshaft Position Sensor and checked voltage again:

    Finally, a bad component! We replaced the Crankshaft Position Sensor and verified that all was well

    Fuel Gauges now work, voltage works, and the low fuel light isn't on anymore

    We started it up and checked the ECM datastream again - all systems go

    Now, the troubleshooting procedure we started out with had us unplug the ECM at the beginning and then test the TPS pin 3 voltage - but these pictures are from us reproducing it after the fact and we forgot to unplug the ECM first... so we logged a code:

    I mention this code just as a side note - we cleared the code with the EVO, but if you just ignore it long enough it'll go away after a few cycles.

Comments (22) Trackbacks (1)
  1. Saved me tons of time , did this check and it fixed the problem !! Bad crank sensor !!!

    Thanks !!

    Shawn

  2. Thank you very much for writing this out in such detail. I just had the exact same thing happen to my 98 ZJ 4.0. Ran fine and then would start. No spark, no fuel, ASD relay good. I noticed that the gauges weren’t coming up when the key was in the run position and that was the search term that found this page.

    Read here. Disconnected CPS harness. Gauges came up. Reconnected = gauges dead. Tried to manipulate wires in case it was a short. Still dead.

    $45, life time warrantied, sensor and it’s back up and running.

    Getting the old sensor out was quick and easy with several ratchet extensions. Dropping the new on in was easy. Getting the bracket/shroud in place and starting the bolt was about 2 hours of very frustrating screwing around.

    Thanks again. I don’t know how long I would have struggled to find this without your help.

  3. thank you for putting in terms i could understand and for the ease of fixing mt problem

  4. great article, saved my saturday.

  5. I have a similar problem with my grand cherokee laredo (2000), the engine shut down while in motion and has refused to start since. Checked everything but no show. The crossed key indicator on the dashboard remains on constantly and there is no fuel supply to the injectors. It cranks fine but doesn’t start, also the light in the shape of an engine comes on once you attempt to crank it. The annalyzer could not communicate with the car at all……no sign and no codes came up at all. My mechanic says the sensor on my key has exopired and I will need to change the key, transponder and brainbox! Is this true?

    • Hi I have the same exact problem you did with your Jeep I was wondering if you found a solution to your problem, Thanks in advance

  6. I have 98 JGCL 4×4 straight 6. Started cutting out at stop signs mostly, then sometimes at high speeds. Threw code ignition coil pack, replaced. Problem still there. Next threw Map sensor code. Replaced. Not fixed. Did research, started jiggling wires. Found that if I put pressure on the ecm, the car would mimic the stalling that was occurring. So I figure there is a crack in the ecm, causing humidity to get in and increase the voltage, throwing codes and cutting engine off. I jammed a stick behind the ecm and tightened the 3 screws down pretty tight (to put pressure on ecm box and maybe close the crack. BINGO jeep runs great for almost a week. Then it rains. Car stalls and wont restart. Thinking maybe the humidity from the rain softened the stick i had behind the ecm and allowed the crack to re-open. Had it towed to an honest mechanic. Bought a new ecm, put it on and still wont start. Sounds like it wants to start. Timing is good. spark is good. But no start. Changed plugs as I had fouled them with gas while trying to start it in the rain (family of 5 in tow.) Cant figure out what is keeping my Jeep from firing up. Sounds like its REALLY REALLY trying hard to start. PLEASE HELP

  7. Sir. Thank you for your post. You were correct. You took many worries off my shoulder. I would like to add that my gas gauge did work, as well as no low fuel light, and my battery showed. Also, the sensor was located on the drivers side under the fire wall. You saved me a lot of time and money. Side note….get the top grade sensor cause I replaced my sensor with the bottom line, my Jeep started but was skipping bad..check engine light came on so I drove it to the same auto store that I bought the sensor from and the code was crankshaft sensor. I upgraded and I am on the rode…check engine light was still on till I disconnected my battery….Thank you again….can’t say it enough….Ray

  8. I have a 97 Grand Cherokee Laredo, has the EXACT same symptoms. I went to my local Jeep dealer, and explained what I had read on this page, and wanted to know if this same procedure would work on my 97, (yours being a 98). I was told that if I unplugged the CPS, turned the ignition on, that if the sensor was bad, my fuel gauge and volt gauge would work, and if they didnt, the ECM was bad. Can you shed any light on this?

  9. That sounds ridiculous. Gauges have very little to do with troubleshooting.

  10. Thanks for this info. We had all the symptoms you described on our 98 Grand Cherokee 4.0. Mechanic thought it was the fuel pump and dead battery. Replaced both and it still wouldn’t start. He was about to replace the pcm until I read your article. I replaced the crank sensor myself and it started right up. First time I was thankful for smaller hands. It was awkward to get to. Thanks again!

  11. I believe I am having the same issue as stated here. All my lights and gauges come on as well as the fuel pump when I attempt to start but it will not turn all the way over. I looked at autozone.com and was told the crankshift positioner sensor was 79.99, I am wondering if I can find one cheaper. I am broke and still have to buy groceries but I need my car to get to work. Can someone shed some light for me.

  12. I have these symptoms. Gas gage does not work engine cranks over no fire. But I changed the crank sensor still have same issue? Any other ideas? Thanks Bruce

    • there is a fuse in the underhood fuse box idk what it was for (lost my owners manual) 20amp mini fuse

      i did all the steps above other than replacing pcm, checked the fuse and it was blown put a new one in and she purrs like a kitten

  13. I have been and ASE master tech for 18 years and have seen many crank sensors fail, but none do this. Read the article and after checking powers, grounds, fuses relays found my crankshaft sensor had failed. Thanks for the helpful information

  14. Fantastic post!!!! This is identical to what happened to my brother in-law tonight in a McDonalds parking lot. Went there with basic hand tools and a meter. Couldn’t figure it out!!! No Gauges! Figured some loss of power to dash or ECM failed. Found this post and sure as heck, unplugged crank sensor and all gauges worked. R&R’d sensor and they were back on there way up North. To Tim who posted 8 months ago; it may sound ridiculous but it is soooooo very true!!!! Thanks again!!!!!

  15. I had the same thing happen and it was a 20 amp fuse in the fuse box under the hood

  16. “What do the gauges have to do with it?”

    Great write up! This is a very common problem and your write up will help a lot of people. Cudos!

    I had the exact same problem with my 98ZJ inline six a year or two ago. I even made the same mistake of replacing the PCM before figuring it out. So, from much research and the painful learning experience of going through this personally;

    A few have asked “What do the gauges have to do with it?” Most of the gauges do not have direct connections to the things they are reporting. For most things, the PCM is connected to the sensor, and it sends a message over the communication bus to the gauge cluster computer, which then moves the needles to the positions it is told to move them to. (a very, very loose analogy; a little bit like e-mail!)

    This “bus” (a pair of wires that connects all the computers so they can communicate) is called the “Chrysler Collision Detection Data Bus” or “CCD” (The word “collision” has nothing to do with wrecking the vehicle, but has to do with keeping the peace between different computers if more than one tries to “talk” at the same time. A “data collision”.) Once again, a very loose analogy; a little bit like an ethernet computer network)

    When you connect a code scanner, you are connecting to this bus, so the code scanner can talk to the various computers on the vehicle.

    There is a 5V power supply in the PCM that powers the internal electronics of the PCM, and many of the sensors connected to it. Often when the CPS fails, it does so in a way that places a very heavy electrical load (a “short” or close to it) on the 5v supply, “dragging it down” (shorting it out) so that the PCM can not work. If a code scanner is connected, the PCM can not talk to it, and it appears to be dead, as noted in the write up. Since the PCM is not sending messages to the gauge cluster, the gauge cluster will do weird things. Also, as mentioned in the write up, if voltage measurements are made at other sensors, they will not be getting the correct 5 volts, they will be low. If the electrical connector to the CPS is disconnected, it removes the heavy load/”short”, the PCM will come back to life, a code scanner can talk to it, and the PCM will send messages to the gauge cluster, and the gauge cluster will do as it is told. (though, the engine will not run)

    The CPS is a bit awkward to get to. I found that if you put together about 30-36 inches worth of socket extensions, you can maneuver so that you can reach it with a socket wrench.

    A new CPS should have installation instructions. There is a thin metal ring on the flywheel with holes in it. As these holes move past the sensor, it detects them, and the PCM can then know what the Crankshaft Position is. The CPS must have the correct clearance/spacing from this ring. The new CPS will probably have a little piece of paper about the thickness of a thick business card stuck to the end with a “post-it note” type adhesive. When you put the CPS into it’s hole, the paper will act like a feeler gauge, and space it appropriately from the flywheel ring when you tighten the bolt. The paper falls off as soon as you start the engine. You will have to do the same thing if you remove and replace a CPS to get it spaced right.

  17. Almost replaced the fuel pump but noticed the gas and voltage gauges weren’t working. I also plugged the scanner in and it came up with error so I went online and found this website. The only difference was that the sensor was on the driver side and had two bolts, but solved the problem and saved a few hundred dollars. Thanks so much!

  18. i have these symptoms. for my 98 grand cherokee engine does not turn over at all!!. changed the ECM and i also changed the crankshaft position sensor and still nothing. any other ideas out there?

  19. Hey guys, I have had the same issues with mine. (It’s currently at the jeep dealer being worked on, woe is me). Anyhow I went through tons of things trying to figure this out. New fuel pump,crankshaft position sensor,coil pack, rotor button,new pcm, new relays. I sent it to the dealer to have the pcm programmedand they said that was all good but had no voltage to the cam sensor. So atm the are putting in a new pickup plate in the distributor. We’ll see if this works. Going through jeep’s recommended fixes for this, they say new crank sensor (but it must specifically be tightened to 16ft lbs. And requires a new grommet if it’s the slotted style in order to receive proper signal from sensing plate). Next jeep recommends new pcm (already done in my case). And lastly to clean out the throttle body (also done). Before I read this a retired ASE jeep mechanic friend of mine had recommended the throttle body clean as the pin gets corroded on the inside and sticks. I’ll see how the pickup plate works out, however I noticed earlier a comment on a possible Crack in someone’s pcm. The issue with that and jeeps wasn’t moisture but vibrations causing the first 4 pins in the pcm to become unsoldered. This part of it can be fixed at home by taking a warm letter opener and peeling the back off of the pcm. Then resolder any pins with bad ohm readings. After the resolder install some foam board behind the pcm to reduce vibrations. (There is a gap of abt 1.5 inches between it and the firewall.wish I had seen that part(was a YouTube video) before I bought my new pcm)

  20. I have a RHD 98 jeep Cherokee. The Gage’s will come on, but it will not turn over. Changed the starter and relay and still there is nothing. I here clicking when we try to start it . Tryed starting it in neutral and still nothing. It can be started when arched with a screw driver. Please help!!


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