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.
- 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/CPK 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/CPK 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/CPK 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.