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sprinkles08
sprinkles08, ASE Certified Technician
Category: Car
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Experience:  ASE Master and Advanced level certified. Factory trained with 14 years dealership experience
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Jeep Grand Cherokee Limited: Brownjeff Good afternoon, Im

Resolved Question:

Brownjeff Good afternoon, I'm from Brazil, the city of barretos and have a problem in my jeep grand cherokee 5.2 v8, suddenly the engine stopped and no more check engine light comes on, no power goes to the coil, lights and other systems normal station, you could give me a light?
Submitted: 1 year ago.
Category: Car
Expert:  sprinkles08 replied 1 year ago.
Hello and welcome to JustAnswer!

It sounds like your powertrain control module (PCM) is down. The PCM is the module that controls all engine functions.

If the PCM isn't awake then the engine light won't do it's bulb check when the key is turned on, you won't have any power to injectors or the coil from the ASD circuit, and the fuel gauge and voltmeter won't work when the key is turned on.

If the PCM is down it could be the PCM itself, a loss of power or ground, or a short on a couple different circuits.

If fuses are ok then odds are the power feeds are ok, but I would test them just in case. A wiring problem or bad ignition switch could prevent the PCM from waking up.

I would also test the grounds.

If the 5v reference circuit shorts to ground it will prevent the PCM from waking up. This circuit goes to the cam and crank sensors, MAP and TPS. A short here could be a wiring issue or internally shorted sensor.

If the sensor ground circuit shorts to voltage it will also take the PCM down. This sensor goes to all engine and trans sensors, again a short here could be a wiring problem or internally shorted sensor.

If the PCM is down and all of these things check out ok then the PCM will need to be replaced.
Customer: replied 1 year ago.

could be the crank sensor (rotation) would not be sending information to the pcm which erased the check engine light?

Expert:  sprinkles08 replied 1 year ago.
The crank sensor could be internally shorted and preventing the PCM from waking up. It's more common on a 4.0 but can definitely happen on a 5.2 also. You can try unplugging it, if the engine light doesn't come on and the gauges don't come up then you can rule out the sensor.
Customer: replied 1 year ago.

Ok since this positive current going to the coil now and has no pulse, the pulse simulator put the hall sensor and nothing, but it still was not the crank sensor, all clocks and lights are working on the panel, even if only to check that engine no, i will try crank sensor before pcm ... if cranck check engine light should come on?

Expert:  sprinkles08 replied 1 year ago.
The positive voltage to the coil comes from the ASD relay initially when the key is turned on and then while cranking.If the PCM is up but the crank sensor is bad you'll have voltage at the coil for 1-2 seconds when the key is first turned on but nothing while cranking.
Customer: replied 1 year ago.

Ok, I'll do the crank sensor replacement. Finally, when unplugging the crank sensor, if defective, the check engine light should go back to work in exact moment ?

Expert:  sprinkles08 replied 1 year ago.
Yes, if you unplug the crank sensor and it was the issue you'd see the engine light come on for a bulb check.
sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 16851
Experience: ASE Master and Advanced level certified. Factory trained with 14 years dealership experience
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