99 XJ engine stall when blower turned on

Good day folks,
Long time googler/ searcher newbie poster.
I have recently purchased a 99 Cherokee sport 4x4 4.0 it has 190k miles. I do have a snapon mt2500 scanner and the cartridges for Jeep. They may be of help if need be.

I am having a few issues which are leading me to believe the PCM may be bad. After googling and searching for months I thought I'd make a post as I'm not getting anywhere on my own.
Prior to changing the starter, and a driver's side hub assembly everything worked well on the Jeep including the A/C after a quick recharge.
My most important issue is with the blower control, ac/ heat. ( yes I have searched but got no reply) on previous threads. No matter the setting, fan speed hot or cold as soon as u turn the knob to ON the Jeep acts as if I cut off the ignition. Possibly 2 seconds the Jeep dies. The RPM gauge drops to zero fuel, temp, battery freeze where they are I believe. Driving, parked same effect. The Jeep will not restart with the blower running. The motor just turns over and over. In order for a restart I have to turn off blower. Cycle the key off then on the fuel pump runs and we fire right up. Parked or driving no difference in behavior. While parked I can turn on the blower and cycle the key the fuel pump never makes a sound. However It does prime with the blower off every time.
Now for the kicker. If i apply the brake all is well while parked. If I feather the brake pedal while driving just slight pressure to illuminate the brake lights heat, AC, all speeds of the blower work fine. The AC is even ice cold! It takes some skill driving with 2 feet. The person following behind me must think I'm nuts for riding the brake. the defrost is a must in rainy days and I gotta do what works! It's a weird topic to Google I found 1 thread where a PCM may have fied and another un answered so I'm looking for a bit of help in my own thread.
Thanks for this wonderful forum and looking forward to working with you guys and gals.

I would go over every ground and make sure they are all good. Grind paint to metal on grounding points, replace corroded wires and connectors. This could he an odd grounding issue.

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Also come to think of it, my blower fan on my 99 has a bad connection and sometimes doesn't work unless i wiggle the wires under the hood where they connect to the fan. Could be a common short point.

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A short to ground or to a 5 volts OBD engine sensor wire circuit is more logical than a PCM fault, especially when the very specific action of turning on the blower fan causes the problem. The brake light behavior supports a wiring or grounding issue as well. Note that blower motor wiring issues are rather common and PCM issues are not. The blower motor circuit suffers from undersized wiring that often leads to blower motor resistor failure, blower motor relay failure, and/or dashboard switch failure. Most of these failures can cause melting/shorting of the blower motor wires.

Check to passenger side kick panel fuse box for water intrusion.

My Jeep is also a 98 but can't see much difference between the two. But for good measure it's a 98.

Ou2mame said:

I would go over every ground and make sure they are all good.
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Click to expand...

I removed the rear panels yesterday to rewire the lift gate.Hoping that odd bunch of wires was a contributor. No cigar The ground points behind the spare tire looked good. Solder and heatshrink spliced in new wires for 3rd brake, defrost and lock. I believe I saw 4 points under the hood? The strap on the firewall in the center. The 2 next to the battery. 1 by the dipstick tube for oil. And the other ontop of the engine block?

Tim_MN said:

A short to ground or to a 5 volts OBD engine sensor wire circuit is more logical.
I am having issues with the idle as well, replaced the AIC with a cheapie off flea bay but doesn't seem to function move.

The brake light behavior supports a wiring or grounding issue as well. Note that blower motor wiring issues are rather common and PCM issues are not. The blower motor circuit suffers from undersized wiring that often leads to blower motor resistor failure, blower motor relay failure, and/or dashboard switch failure. Most of these failures can cause melting/shorting of the blower motor wires.

Click to expand...

Hopefully we can remedy something prior to disassembling the dashboard and such. I will poke around here thanks for the response. As far as the IAC and tps I plan to post those issues next I was just trying to weed out the most important to me at the moment.

shelbyluvv said:

Check to passenger side kick panel fuse box for water intrusion.

Click to expand...

This fuse box is beind the trim under the dash by the door? I don't see an access panel on my Jeep. ..

There's also 2 or 4 ground points by under the air box towards the fender

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The ground I would suspect is G108 ...behind the kick panel down low next to your left foot when your sitting in the drivers seat.

If you can't find your fuse panel this issue is beyond your repair. I'm not being a dick, well maybe I am. Come on man, check your passenger side, foot well fuse panel.

Automechnic077 said:

My most important issue is with the blower control, ac/ heat. ( yes I have searched but got no reply) on previous threads. No matter the setting, fan speed hot or cold as soon as u turn the knob to ON the Jeep acts as if I cut off the ignition. Possibly 2 seconds the Jeep dies. The RPM gauge drops to zero fuel, temp, battery freeze where they are I believe. Driving, parked same effect. The Jeep will not restart with the blower running. The motor just turns over and over. In order for a restart I have to turn off blower. Cycle the key off then on the fuel pump runs and we fire right up. Parked or driving no difference in behavior. While parked I can turn on the blower and cycle the key the fuel pump never makes a sound. However It does prime with the blower off every time.
Now for the kicker. If i apply the brake all is well while parked. If I feather the brake pedal while driving just slight pressure to illuminate the brake lights heat, AC, all speeds of the blower work fine. The AC is even ice cold! It takes some skill driving with 2 feet. The person following behind me must think I'm nuts for riding the brake. the defrost is a must in rainy days and I gotta do what works! It's a weird topic to Google I found 1 thread where a PCM may have fied and another un answered so I'm looking for a bit of help in my own thread.
Thanks for this wonderful forum and looking forward to working with you guys and gals.

Click to expand...

Interesting problem.

As suggested, power may be introduced in to a ground circuit via a short.

What is interesting is the fact that when you depress the brake pedal, the system(s) return to normal.

The fact that you lose instruments and the engine dies points to the CCD Bus being corrupted.

The ground that may be the focal point is G108 (as mentioned).

G108 is the ground for the HVAC mode selector and the TCM and PCM Brake Lamp Switch Sense. The Brake Lamp Switch Sense is the ground circuit for the TCM/PCM transmission overdrive lock up.

There are three sets of switch contacts in the Brake Lamp Switch.

One set (pin 5/6) is normally open and when the brake is applied the contacts close, putting the brake lamps on.

Another set (pins 3/4) is normally closed, providing the ground circuit for the Cruise Control Servo (it is grounded at G106 on the left inner fender). When the brake is applied the switch contacts open, killing cruise control.

Another set (1/2) is normally closed, providing the ground circuit for the TCM/PCM overdrive lock up and the shift interlock circuit (it is grounded at G108, same as the HVAC Mode Selector). When the brake is applied the switch contacts open, removing the ground to the TCM/PCM overdrive lock up. This circuit may be corrupting the CCD Bus.

First, try removing fuse F25 from the Junction Block. This fuse powers the shift interlock solenoid, which is spliced in to the brake lamp switch sense circuit and is grounded through the brake lamp switch to G108. This fuse also powers the HVAC blower motor relay control coil and the blend air door actuator. See if the problem exists with this fuse removed (with and without depressing the brake pedal). If no help, reinstall fuse.

Fuse F6 (40A) in the PDC powers the HVAC blower, which is grounded through the mode selector to G108. If no results from removing F25 from the JB, remove this fuse from the PDC and see what happens.

I have no resolve at this point but these steps may help point in a direction.

PDC:



JB:

Sidewinder CC said:

Click to expand...

I pulled F25 and got a no start condition foot off and on the brake. Put fuse back in started right up. Pulled fuse and engine died both brake and no brake.

I installed F25 back in place and moved onto F6 in the PDC pulled that out and no start. Put foot on the brake and it started right up. Took foot off brake and it died..

I paid a bit more attention with all fuses installed engine running. Turn on blower rpm drop to zero. Oil and fuel freeze. Turn off blower they then fall

shelbyluvv said:

If you can't find your fuse panel this issue is beyond your repair.

Click to expand...

Thanks for the tip. The plastic is covered in suede material from the girl who owned it before me. I didn't see the cut out

Automechnic077 said:

I pulled F25 and got a no start condition foot off and on the brake. Put fuse back in started right up. Pulled fuse and engine died both brake and no brake.

I installed F25 back in place and moved onto F6 in the PDC pulled that out and no start. Put foot on the brake and it started right up. Took foot off brake and it died..

Click to expand...

Extremely odd.

Removing fuse #25 from the Junction Block should not prevent the engine from starting or kill it while its running. See diagram of what F25 feeds.

When you were pulling F25 did you have the mode selector OFF or in some other position?

PDC F6 being pulled and no start is puzzling as well.

Here's some diagrams you can look at.

Your HVAC Blower circuit. Note the function of F25 and F6. And ground G108.



Here's what JB F25 powers.



Here's the G108/brake lamp switch interface:



Figuring out electrical problems on these XJ's can be as hard as Chinese arithmetic.

You may have corrosion issues with your JB.

Gain full access to the JB by removing the trim panel.

Unplug connector C4, and a few others and see if there's corrosion on the pins and pin cavities.

I removed the drivers side lower trim kick plate by the hood release . I don't clearly see a ground point there.G108 Is it above the giant square plug of wires? I didn't have much luck searching the forum for a picture of it either. I found a post saying it's above the hood release I'll look tomorrow

Sidewinder CC said:

Extremely odd.wh
en you were pulling F25 did you have the mode selector OFF oror in some other position? The mode selector was off. Pulling the fuse F25 I could hear something click and everything shuts off and acts just like it does WITH the knob.

PDC F6 being pulled and no start is puzzling as well.
started with foot on brake. So opposite of the original issue. I didn't try the ac as we pulled that fuse.

Here's some diagrams you can look at.
are these from a FSM they are really nice.
Your HVAC Blower circuit. Note the function of F25 and F6. And ground G108.


Figuring out electrical problems on these XJ's can be as hard as Chinese arithmetic.

You may have corrosion issues with your JB.

Gain full access to the JB by removing the trim panel.

Unplug connector C4, and a few others and see if there's corrosion on the pins and pin cavities.

Click to expand...

Automechnic077 said:

I removed the drivers side lower trim kick plate by the hood release . I don't clearly see a ground point there.G108 Is it above the giant square plug of wires? I didn't have much luck searching the forum for a picture of it either. I found a post saying it's above the hood release I'll look tomorrow

Click to expand...

Don't worry about G108 at this point. There many circuits grounded there. If the ground was defective in some way the other circuits would be affected.

Does your Jeep have an aftermarket radio?

Sidewinder CC said:

Does your Jeep have an aftermarket radio?

Click to expand...

Stock radio, factory fog lights however the switch is removed. I don't see the switch tying into anything here.
I feel like I'm in for a long ride...

I will check for corrosives this afternoon when I get off work.

This rain has been killing my progress. I got the side panel off the JB and unplugged and replugged most of the bigger plugs. It all looks brand new. No signs of corrosion. Or heat

Why does the edit post option disappear after some time?I sure would like to be able to post via mobile and edit or add to the post later via PC or phone.

Would the pcm have no effect in any of this?
Is it recommended to buy a eBay so called rebuilt unit? So many wishy washy answers.

Maybe every 60 -100 miles or so the just dies trucking down the highway at 60 mph. Usually requires to be put in neutral then starts right up. This last time today it however cut off ) then before I could shift into neutral it just picked back up and was running again. Yay me... (similar to turning off the key while driving).
Dealer paperwork in the glovebox claims that in 2010 the CPS was replaced.
I replaced water pump, radiator, charged ac. Everything was good.

Next week I replaced starter, passenger hub bearing assembly, front pads, and new door speakers.
I did pull the bezel off the dash and the radio out to verify audio output prior to removing door panels, while apart I investigated to find out why my factory fogs wernt getting power. Noticed switch was melted from small wiring bad design. didn't notice anything out of the ordinary inside.
The only odd thing was I disconnected the battery prior to removing the starter. On reinstall the cable moved back to the positive battery terminal and as I shoved the starter up it arched and scared the crap out of me. Could that arch have caused something?
I have inspected the pcm plugs and pins, added a separate ground to the casing, via the front most screw. Trying to solve the scanner codes previously.
ENG.
P0505 Ais AIC shorted.
TRANS.
P0122 TPS
P1694 CCD message from JTEC failure

Could a bad tps allow 5v to be introduced into the ground circuit and throw everything into an uproar?
I know I jumped off topic from my original problem but maybe this will be helpful???? I'm digging up everything from my memory bank.