Jeep Repair Problems? Ask a Mechanic for Answers ASAP
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When this happens, the pcm is down. It could be the controller itself (not likely since it was replaced) or an outside electrical problem that is taking it down. A lost power or ground feed to the module, a sensor ground circuit shorted to voltage, or a reference voltage circuit shorted to ground will all cause the engine controller to go down. You will have no spark, no fuel pressure, the fuel gauge and voltmeter on the dash won't come up with the key on. There won't be any communication with a scan tool because the pcm is dead to the world. A common cause for this is an internally shorted crank position sensor. This is mounted at about the 11:00 position on the bellhousing as viewed from behind, and the electrical connector comes up to the back of the intake. Start by unplugging the crank sensor and see if the fuel gauge and voltmeter come up. If they do, replace the crank sensor. If this doesn't make the gauges come alive you'll need to do some deeper electrical testing to see why the controller is down. I would start with the powers and grounds, then move on to the reference voltage and sensor ground circuits. I can help you with that if you've got a voltmeter and want to get into some testing while it's acting up.
The sensor is mounted at the bellhousing, the pigtail comes up into the engine compartment and is at the back of the intake manifold. There isn't another three wire electrical connector in the area. Have you found the sensor from my last diagram? The sensor should be easy to spot from underheath with a flashlight. Once you find the sensor and know what area it is in you can see which direction the wiring goes to know where to look from the top side. On the older 4.0 the connector ended up on the right side of the engine block near the distributor but that should not be the case with yours. Find the sensor and you will be able to see which direction the pigtail goes for sure and you'll find the connector.