• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

no bus

davidson99XJ

NAXJA Forum User
Location
Greensburg IN
Wth??? Jeep will start and run for like 2 seconds then shut off. Also none of the gauges work. Whats going on????
 
Crank position sensor?

CPS


The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP). CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again when it cools back down.


Symptoms –

- Starter cranks and cranks but engine won't start up
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump will run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBDII code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is the culprit and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.

CPS Testing


Crankshaft Position Sensor Connector (CPS/CPK)


standard.jpg



TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not the drivers side as shown in the diagram below. Simply follow the wire from the sensor to the connector.

.
standard.jpg
 
It will start just fine just like normal. And after a couple seconds its like you turned it off. It just does and no bus comes up on the odometer. And i only have lowne key amd it has worked fine this whole time . just did this this morning.
 
The Factory installed alarm system will do that when it goes bad. Do you have light gray keys or black keys (or bare metal) ? Is there a module just forward of your ignition cylinder ?

.
standard.jpg
 
Grey key. And I'm not sure. I keep it locked. And my toolbox key for work is on my jeep keys. So I took my keys to work and since I couldn't drive it today of course I walked out and left my keys at work. With my jeep here at the house.....no chance of working on it this weekend now...great
 
Went to town this morning amd got my keys from work. Came home and the junker started right up....maybe it did it because it was so cold yesterday morning?....
 
Do you, or do you not, have the factory installed Sentry Key security system ?
 
If you have the factory security chip key (SKIM) anti-theft, and it goes bad, it is cheaper and easier to remove it, than to have it repaired. Simply remove the steering column chip reader module and install a good used ECU from a non chip key Cherokee that has the same part number. The ECU just needs to be from the same model year donor, and have the same engine/transmission. The ECU will not need to be re-flashed. If you do not remove the SKIM module it will lock up the fresh ECU and the Cherokee will start, run for 2-3 seconds, and shut off.
 
Back
Top