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Brad
Brad, Jeep Dealership Tech
Category: Jeep
Satisfied Customers: 3686
Experience:  16 Yrs Chrysler/Dodge/Jeep. ASE Master (L-1) Certified
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Jeep Cherokee: I have a 1996 Jeep cherokee sport (xj), 4 door,

Resolved Question:

I have a 1996 Jeep cherokee sport (xj), 4 door, I6 engine that keeps blowing the 30amp mini fuse in the PDC (under the hood). This kills the truck while running and will not allow it to restart. I've replaced the fuse and its run for awhile - then blows out again...does it more off road than on road. I can't find any diagrams online for the PDC - and my owners manual only shows one 30amp mini - which says, coil, fuel pump, ignition, etc...The engine turns over, but no spark...
Submitted: 2 years ago.
Category: Jeep
Expert:  Brad replied 2 years ago.

Brad :


Hello and welcome to JustAnswer, My name is XXXXX XXXXX I will be assisting you.. Do you know what fuse number it is?


Brad :

Maybe fuse 20?

Customer:

I don't have it in front of me - its stuck on one of the back fields of my farm

Brad :

Ok, I looked up the wiring and I believe its fuse # XXXXX which is a 30amp and controls Coil, Ignition, Etc...

Customer:

lets roll with that assumption

Brad :

There is a wiring of that fuse.. How ling does it take to blow the fuse?

Brad :

*Long*

Customer:

took awhile at first - could replace and go...

Customer:

Last night - as soon as u cranked the engine it blew - car was very hot

Brad :

And now does it blow as sonn as you install it?

Customer:

went thru 4 fuses

Customer:

yes

Brad :

Ok, great! The issue will be easy to find then.. If you can read the Wiring Diagram.. That fuse supplies to Coil, Alternator, PCM, O2 Sensors.. I would like for you to start unplugging these one at a time until the fuse stops blowing.. And based on the my history, Id start with the O2 sensors

Brad :

If you get back out there and the fuse isnt #20, post back and I will be able to get you the correct wiring diagram

Customer:

gotcha - read that - if that works..replace that component?

Customer:

will do

Brad :

Correct!!! The component you unplugged and it stopped blowing, replace that component...

Brad :

If you need anything else, feel free to ask... Im here to assist you in repairing your vehicle

Brad :


Well I want to Thank You for choosing JustAnswer. It was my pleasure assisting you, and if you have any future questions feel free to Request me


http://www.justanswer.com/car/expert-dodgetech77/ Thank you and have a greatday!!!!! Brad

Brad, Jeep Dealership Tech
Category: Jeep
Satisfied Customers: 3686
Experience: 16 Yrs Chrysler/Dodge/Jeep. ASE Master (L-1) Certified
Brad and 2 other Jeep Specialists are ready to help you
Expert:  Brad replied 2 years ago.
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Customer: replied 2 years ago.
OK - no number for the fuse on the PDC - owners man does schem does not look like the pdc I have - but I believe we are still talking about the right fuse....So ....OK - I've unplugged both o2 sensors - still blew the fuse. Unplugged the two wire (with quick attached clip) on back of coil - still blew fuse. Unplugged the one to two connector to alternator and still blew fuse. Unplugged all three connectors to pcm and did NOT blow the fuse...Is there any better way to test - should I recon some of the pcm connectors to isolate?
Expert:  Brad replied 2 years ago.

Here is another wiring:

 

graphic

Expert:  Brad replied 2 years ago.
Unplug the Cam and crank sensors and see if fuse still blows....
Customer: replied 2 years ago.
How do I read that diagram? PCM has 3 plugs....standing behind the PCM the color of the plugs from right to left is grey, white, black... As I read this - I would uplug the rhs connector and middle connector... Can you confirm?
Expert:  Brad replied 2 years ago.

Plug all of the back in. We are going to check the Crank sensor and the Cam sensor.. But for reference the Black connector is C1, the White is C2, and the Gray is C3... The Cranshaft sensor plugs in on the back side of the passensger side of engine...

 

graphic

Expert:  Brad replied 2 years ago.
And the Camshaft sensor is the distributor plate... Let me know what happens..
Customer: replied 2 years ago.
do you mean the plug that comes off the dist plate?
Expert:  Brad replied 2 years ago.

That is correct.. Here is pic

graphic

Customer: replied 2 years ago.
The picture you sent if diff frommy truck -my manifold comes out on driverside - it looks like I have a sensor there coming from where the tranny ties into the engine. The only other plug on pass side with wires coming out is a large harness of plugs...I didin't see a large harnes in the diag. Can u confirm?
Expert:  Brad replied 2 years ago.
The Crankshaft sensor you see is mounted on the top of the drivers side of the bellhousing.. But the connector routes around to the back side of the passenger side of the engine.. You may need to identify the crank sensor then follow the wiring arounf to the connector...
Customer: replied 2 years ago.

OK - I do see that - and I can see the wires come from there (3 wire connector) up the drivers side to a plug.

 

Expert:  Brad replied 2 years ago.

It may be routed a different way... Try and locate the sensor and follow the wires to the plug.. Here is another pic of where it maybe

graphic

 

 

graphic

Customer: replied 2 years ago.
got it! - that blew the fuse
Expert:  Brad replied 2 years ago.
So unplugging it the fuse didnt blow, but plugging it in did? Please confirm so I know where we are at.. Thanks Brad
Customer: replied 2 years ago.
No - we unplugged the dist sensor and the crankshaft sensor and blew the fuse. When we unplugged c1, c2 and c3 of the pcm - thats the only time we could crank without blowing the fuse.
Expert:  Brad replied 2 years ago.
Ok, do you have an Ohm-Meter? I want to remove the ASD Relay and test some things
Customer: replied 2 years ago.
Yes - what is the ASD relay?
Expert:  Brad replied 2 years ago.

ASD (Auto-Shut down Relay) its the Relay that the fuse powers up.. Also I really would like to confirm the fuse we are working on.. The lid doesnt have a number on it.. Underside or topside?

 

Customer: replied 2 years ago.

There is no numbers at all - Even the owners manual doesn't help! Its the only 30amp mini fuse and its right next to a 20amp mini -

 

would picture help?

Customer: replied 2 years ago.

Here is a picturegraphic

Expert:  Brad replied 2 years ago.
Ok, sorry it took so long... I had to break out an old book.. Well we are correct, it is in fact Fuse 20.. Do me a favor.. Hook everything back up and remove the fuel pump relay.. See if fuse blows
Customer: replied 2 years ago.
Yes it did blow that fuse - that was my last fuse...I'll need to go into town..
Expert:  Brad replied 2 years ago.
Ok, to keep from blowing anymore fuses I want to use the Ohm-Meter.. I want you to remove the ASD relay and install the lead into pin 87.. The slot isnt numbered but you will need to turn the relay upside down and look for 30-87-85-86.. Find where 87 would connect in PDC and get a Spade terminal or something to insert in there to connect the Ohm-Meter.. Set it on "Beep" Ohms if it has that function... Then touch the other side to ground post and see if it beeps..
Customer: replied 2 years ago.
how do I identify the asd relay?
Expert:  Brad replied 2 years ago.
Its labeled under the lid... Remove it and you will see 2 slots that are facing the same way, and 3 that are facing the same way.. 87 is one of the 2 that are facing the same way.. I think its the one to the inside..
Customer: replied 2 years ago.
the posts are labeled 1-5 with a diag on the relay - post 5 is one of the two in the same direction and it beeps the ohm meter. The outer one does notgraphic
Expert:  Brad replied 2 years ago.
Ok, I have been doing some digging and it looks like this is a common issue.. And most of the time it is a shorted O2 sensor wiring at the heat shield.. Can you look under the vehicle at the O2 sensor wiring and follow it up thru the harness to see if you see bare wires.. And you are correct, it is Pin 5.. That relay is numbered diffferently but its 5..
Customer: replied 2 years ago.
Which heat shield? At the cat or up along the engine?
Customer: replied 2 years ago.
Which heat shield? At the cat or up along the engine? Which sensor? Upstream sensor or one below the cat?
Expert:  Brad replied 2 years ago.
Both Upstream and downstream run in the same wiring harness... What Im reading doesnt say where the shield is.. But the wiring harness will be rubbed thru by the shield.. Im trying to find a pic for you..
Customer: replied 2 years ago.

OK - mine is different - the upstream o2 sensor you can follow up to hard plastic encased square harness that runs along the fuel dist bar - the second downstream sensor runs up to a larger harness that come up behind the rear of the engine on the passenger side.

 

All the wire harnesses (plastic tubing looks to be in excellent shape from the senor to their terminous as descrbed.

Expert:  Brad replied 2 years ago.
Is the fuse only blowing when you start it or as soon as your turn key on? I know that the fuse didnt blow when you disconnected the pcm..And I dont want you thinking that it is a PCM issue.. The PCM needs to be hooked up in order for it to power on the ASD relay.. When the ASD relay is powered on it connect pin 30 and 87 to the rest of the circuit.. I still feel that this is a wiring or sensor issue.. And to make sure.. Earlier you disconnected the Alternator, O2 Sensors, Coil, Fuel Pump, Injectors, and it still blew the fuse.. If not disconnect these components and test the Pin 87 to ground if it still beeps then wiggle wires and see if beeping stops... This isnt going to be an easy fix.. Elecrical and wiring issues take time to correct...
Customer: replied 2 years ago.

No - I can turn the ignition on - just before crank and it doesn't blow. As soon as I crank the starter - the fuse blows.

 

When I tested pin 87 to ground - I think I had the blown fuse still the fuse panel - should I have replaced the fuse - and then tested?

 

Yes - I've disconnected all those items and I'm still blew the fuse in the exactly the same fashion.

 

Do you want me to disconnect all those items at once and then test pin 87 to ground?

 

EVen though my ohm meter sounded the alarm - I did stillmeasure about 3-4 ohms of resistence - it did not go to zero (pin 87)...

 

T

Expert:  Brad replied 2 years ago.
Ok, the fuse being blown or not doesnt matter when the relay is removed.. And yes, I would like for you to remove everything from the circuit and see if it still beeps.. The PCM is on the circuit just to see the 12v to verify the the ASD is on.. It controls the ASD thru Ground circuit on either pin 1 or 2.. The other pin 1 or 2 is 12v from the ignition switch...Connector C3 pin 3 is the wire that turns on the ASD relay, and C3 Pin 12 is the wire from the ASD that the PCM verifies the ASD relay is on.. So lets disconnect everything, and then see if it beeps..
Customer: replied 2 years ago.

OK - with everything disconnected - there is no continuity between ground and my pin 5 (pin 87).

 

As I reconnect everthing - there is no continuity until I bring the o2 sensors on. Once they are plugged in - I get continuity...

 

I doesn't matter which either or...or both connected cause continuity between the asd pin 5 and ground...

 

What does that mean?

Expert:  Brad replied 2 years ago.
Ok, Did you connect everything even PCM and you have no Continuity until you plug in the O2 sensors? If so, replace fuse, connect everything except O2's and start engine.. See if fuse blows
Customer: replied 2 years ago.

Yes - that is correct - just did - car started...But this is basically the same test I did first when we started this...I've already blown a fuse with both o2 sensors disconneced...

 

So now what???

 

kinda makin me think the sensors are OK - and there is a bare wire somewhere finding ground between the sensor plug and the pdc?

Expert:  Brad replied 2 years ago.

You dont have any continuity until you connect the O2 sensors..But the fuse still blows when you start vehicle with them disconnected.. Well If it was the O2 wires it would have continuity when they was disconnected.. Did you try and wiggle the wires when it was disconnected to see if the beep came back.. When you start the vehicle the shaking may allow the bare wires(if any) to touch ground.. And that is exactly what Im finding when I do a search for fuse 20 blowing.. So we may be onto something if we can trace it down... I will reply faster now that Im at home.. And by the way you have been doing an excellent job in testing this with me today..

Customer: replied 2 years ago.
Thanks - yea - thats what I'm thinking - I'll try to test that once my wife gets home and see if I can wiggle the wires about - with them disconnected and make ground. With either one of the o2 senors connected - I get continuity on node 5 - IF I can't make a connection with the sensor wires do I replace one or both of the o2 sensors?
Expert:  Brad replied 2 years ago.
Well I wouldn't replace either one if you are still blowing fuses and they are disconnected... Isn't that correct, that you didn't have continuity on pin 5 with them disconnected but it still blew the fuse? And you had continuity with then connected?
Customer: replied 2 years ago.

I had continuity with them connected. No continuity with them disconnected. The car did start and I did not blow the fuse (this afternoon).

 

But I know this was the first test I ran this morning...BUT...I may have used a 20amp fuse instead of the 30amp fuse this morning...Reason being is I'm an hour from the auto store and I had only one 30amp fuse left AND I had started the car a couple weeks ago on 20amp fuse after blowing the first 30amp when the problem first arose...The 20 amp lasted long enough to get back forth from the autoparts store and then it was replaced with a 30 -which blew a day later...while driving - then the next 30 lasted a week...It wasn't until last night pulling a tractor out of a brush fire that the fuse blew again (yea - great timing)...It didn't restart till this afternoon.

Expert:  Brad replied 2 years ago.

Im glad it didnt get burnt up in the fire.Cool But when you tested the Ohm's did you notice if one of the O2's were closer to .001Ω because a perfect wire is .001Ω and it one O2 is .167 and the other is .001-.050 then its shorted to ground.... I scrolled above and you did mention that you tested 3-4 Ω.. Was that with both O2's connected?

 

Lets test each one and see if they are different readings.. And test on Pin 5 at ASD relay..

 

Also when you wife arrives, disconnect both and wiggle the entire harness to see if you get a "Beep"...

 

We are getting closer, but need to narrow it down more... And when you say that is lasts longer with a 30AMP fuse than it does with a 20Amp.. That makes me think we are dealing with a high resistance circuit, rather than a shorted circuit.. If you understand what im saying...

 

Test that and post back results..

 

Thanks Brad!!

 

 

Customer: replied 2 years ago.

OK - here's what we found:

 

Rear o2 sensor cable plug to engine seems ok - no matter how I twist it - it does not send pin 5 to ground. Connecting it does.

 

The front o2 sensor - same deal but this one changes. When its connected - it goes to ground - but sometimes not - most of the time its at ground - I can twist and pull it and change it - but cannot keep it from making cont with ground. So while I rested under the car - with it plugged in - it just stopped - the ohm meter stopped the beep...witht the sensor plugged in - then I couldn't get it to start beeping again. Then I unplugged it - no change - then plugged it back in and it started beeping again.

 

I don't think this is any new information - thats just damn weird....

 

T

Expert:  Brad replied 2 years ago.

What? That is kinda wierd.. But with that and earlier you said that with the O2 unplugged it still blew the fuse.. Im feeling that its wiring.. But finding it will be having to tear out the wiring and inspecting it all the way to the PDC....

Customer: replied 2 years ago.

Yea - I've been working on since my last post...I've traced the leads as far as I dare not making any change to the continuity - I've wiggled and pulled every harness, lead and connector into which the o2 sensors are connected and nothing but continuous continuity to ground on node 5 of that relay.

 

Have not gotten back to no continuity unless BOTH 02 sensors are unplugged.

 

I lifted out the pdc so that I could wiggle all those wires into the pdc and still no confirmed change (that was tough with ohm meter stuck into the node)..

 

Is it worth knowing what the wire colors on the 02 sensor mean? There are 4 - two white one grey and one black - gonna guess sensor, heater, and maybe two separate grounds? What heats the o2 sensor??? That would be hight resistence I imagine...

 

I don't know...

 

Any other suggestions????

Expert:  Brad replied 2 years ago.

I would say its the O2 sensors, (IF) you could run the vehicle fine with them unplugged and the fuse not blow..And you cannot as you tested earlier... Next: When you tested earlier and you pulled and changed the beep, that sounds like wiring.. And for your O2 wiring, I will give you a little info:

 

On your O2 is 4 wire, that lets you know that its a heated O2 sensor and not a old 1 wire, There are 4 wires.. 1 gray, 1 black and 2 white.. The 2 white are the O2 sensor heater, one is 12v and the other is ground(It doesnt matter which way you hook them up), and the Gray is sensor ground and the black is O2 signal.. The newer O2 sensors have heaters to hurry and get them to 600 Deg, (WHY) because that is when they start producing voltage... Yes I said producing voltage.. They have zirconium in them, which usually produce a max voltage of .09v.. When the vehicle is rich(to much fuel) voltage is high, and lean signal is low voltage..
The PCM uses this info to adjust the Pulse width of the injectors to get the best engine performance and less emissions..

Ok, enough of the O2's

Well it would be nice if you could get the wires to act up... But it seems like they are not going to.. And when it still blew the fuse with them unplugged points at the wiring or something else causing this issue..

I didnt ask,, but was the check engine light ever on.. If so do you know what the codes were?

Customer: replied 2 years ago.

The only time the CE light came on the car died at 40mph (yep - the fuse blew) and one error code was produced (twice) P0201

 

I assumed the misfire was caused by the fuse blowing with the vehicle under power...

 

So whats next - replace both O2 sensors?

Expert:  Brad replied 2 years ago.
When did the P0201 set.. That is a Injector #1 control circuit.. And the same wire we are dealing with to the O2 sensors...DG/OR... and if that wire was shorted it would blow the fuse..

Maybe on to something here, inspect the Injector #1 wires and open up harness that has all the injector wires in them to see if you see anything..
Customer: replied 2 years ago.
It set about 10 days ago - like I said the truck cut out on me going 40mph - its the only time it set off the CE light producing a code. I was right in the middle of the road when it died - I popped out the blown fuse with a new one, it started right up and I drove it for 8 days (intermittantly) after that...
Expert:  Brad replied 2 years ago.
Ok, well like I said... That is the same wire we are chasing when you are disconnecting everything.. Set the Meter on ohms (Beep) and see if wiggling the injector harness/wires to see if you can find the short there...
Customer: replied 2 years ago.

Yep - will do - I had to get into the office today so I'll check that this evening...also plan to buy two new 02 sensors and plug them in (without install) to see if it creates the short - then maybe touch the nut threads to the muffler to see if that creates the short too...

 

Its hard to understand how plugging them in completes the circuit to ground somewhere unless the sensor itself is causing the short to ground - but why both and why no rich/lean error codes???...I can't answer...

Expert:  Brad replied 2 years ago.
Well inside the O2 sensors are the heaters..The heaters are closed circuits directly to ground on the other side.. That is why you had continuity.. But losing it when you pulled on it would point at a wiring issue.... also having continuity when they arent connected also points to wiring... And the injector code is another wiring issue..... Let me know what you find.. Im here to assist in any way I can.. Thanks Brad

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