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sprinkles08
sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 17104
Experience:  Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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97 jeep grand cherokee laredo: 4.0 shut..gauges..volt

Resolved Question:

My 97 jeep grand cherokee laredo 4.0 shut down while driving. no gauges work,volt.,gas tank,oil press.,and temp are not working but the lights works the check engine light works odometer and the rest of the warning lights. car turns over but wornt start. im getting no voltage to the coil. I'v checked all the fuses inside and out and the relays there all working I'v chcked the computer.
Submitted: 5 years ago.
Category: Jeep
Expert:  sprinkles08 replied 5 years ago.

Hello and welcome to JustAnswer!

 

 

When this happens, the engine controller (pcm) is down. It could be the controller itself 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, and 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.

Customer: replied 5 years ago.
Unplugging crank sensor didn't work the scan tool won't pick up anything
Expert:  sprinkles08 replied 5 years ago.

Ok. We'll have to break out a voltmeter and do some electrical tests. Do you have a meter?

 

Customer: replied 5 years ago.
Yes I do but it won't be tonight contact tomorrow thank you
Expert:  sprinkles08 replied 5 years ago.

Sounds good. Let me know when you're ready to go!

 

Customer: replied 5 years ago.
Ready to go
Expert:  sprinkles08 replied 5 years ago.

I'm tied up at work this afternoon. I'll get back with you just as soon as I can!

 

Expert:  sprinkles08 replied 5 years ago.

Ok. Let's start by checking a couple voltages at the TPS or MAP sensor on the throttle body. TUrn the key on and unplug either sensor. Check the voltage on all three wires and let me know what you get.

 

Customer: replied 5 years ago.
.07 wht/blk .06 org/blk .00 bl/blk on tps sensor
Expert:  sprinkles08 replied 5 years ago.

Ok great. We know the pcm is down for sure.

 

Let's check the pcm powers and grounds. Unplug the black connector, look at the inside and you'll see that the terminals are numbered. With the key on check for power on pin 2 and 22, and ground on 31 and 32. 32 isn't numbered making it look like there are only 31 wires.

 

Customer: replied 5 years ago.
Pin 2 12 volts pin 22 no voltage 31 & 32 continuity to ground
Expert:  sprinkles08 replied 5 years ago.

That's excellent. That made or nights better!

 

Pin 22 gets direct battery voltage from fuse 20 in the power distribution center, the fuse box under the hood. Double check all fuses over there with a test light on both terminals to make sure it lights on both. If you for sure don't have any blown, take note if fuse 20 actually has power or not. If it doesn't have power to it from the start we'll have to track it down. If the fuse does have power but not at the pcm you've got a broken wire in between the fuse box and the pcm.

Customer: replied 5 years ago.
All fuses are in tact and working
Expert:  sprinkles08 replied 5 years ago.
I know you said you checked them, but we need to make sure if we have power at fuse 20 or not. If we do have power there and the fuse is good you have a broken wire between the fuse box and the pcm. If the fuse has no power we'll have to chase down where the power comes to the fuse from.
Customer: replied 5 years ago.
Which fuse is fuse 20 there not numbered I just put the meter on all the fuses under the hood and there all reading 11.95 volts on both pins of every fuse
Expert:  sprinkles08 replied 5 years ago.
Ok. If every fuse does have power for sure you have a broken wire between the fuse box and the pcm, or a problem inside the fuse box itself. You could open up the harness and look for the break or corrosion spot, or you could run a new wire to the pcm from the box.
Customer: replied 5 years ago.
Great I have gauges but still No voltage at coil
Expert:  sprinkles08 replied 5 years ago.
You aren't going to have voltage at the coil if you just turn the key on. It and the injectors get voltage from the ASD relay. This relay will power up at key on for about 1-2 seconds and then go out. Assuming good cam and crank signals that line up with each other, the relay will power back up when you crank the engine.
sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 17104
Experience: Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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