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99 XJ engine stall when blower turned on

I took out the blower motor resistor this morning disassembled it and checked continuity across the thermal fuse. I have none so this is blown. That will explain my single fan speed but not why the truck only runs with the fan on 4 and the ac selector OFF!
Stupid me ran the fan with the BMR dangling in the cab. I assume that's what killed it!
 
I have traced the white/pink and also the Lt green from pins 23,24 from the pcm into the cab. Undid the white wire keeper mounted under steering wheel part of the dash ( I hope they all go back in there!! ) Checked all the wires in that mess.
The white/pink brake sense wire goes into the TCM, the brake switch and up the steering column into a small 2 prong connector.
Also did a few things. If I unplug the brake switch off the pedal I get a happy Jeep. Ac / heat compressor comes on aux fan runs. Everything seems normal. Except I obviously have no brake lights.
With the brake switch unplugged I unplug the small 2 connector white/pink wire from the steering column no issues as long as I'm on fan speed 4. 3,2,1 immediately kill everything. if I turn the mode knob to any position the Jeep dies as well even on fan speed 4. Also remember the BMR is not present in the wiring loop! For any of this as I burnt it up.

Can a brake switch be causing all this?
Sorry to post so many posts I'm just trying to offer as much info as possible
 
just to clarify... when the mode switch is in the off position the blower doesn't turn on...correct?
The small 2 prong connector to the steering column goes to the brake transmission shift interlock solenoid.
Can check for voltage between ground and the pins on the brake switch connector cable when you have it unplugged with the key on and let me know what you get for readings?

The main functions of the brake switch are to tell the PCM to adjust IAC to idle rpm speed while braking, tell the antilock brake computer you are braking, to tell the TCM you are braking, to enable/disable the transmission shift interlock solenoid so you cant shift out park without your foot on the brake, and turn your brake lights on and off, and deactivate speed control servo.
 
No the blower doesn't run unless the mode is switched from off.
Key run Engine off grounded to g108 unplugged
White/pink brake switch sense11.67
BLACK ground 0
OR/DG speed control power supply 0
DB/RD speed control brake switch output 0
WHT/TN Brake lamp switch output 0
PK/DB fused B+ 12.23
 
The PK/DB should be hot at all times, this is the fused battery feed, this connects to WHT/TN when the pedal is depressed and feeds the brake light circuit.
YL/RD will be hot with the cruise in the on position.
WHT/PK should have a low voltage feed on it for the PCM to monitor brake switch position, with the pedal released this goes to ground and with the pedal pushed it does not.
That's my understanding of the switch. Is 11 volts considered low voltage? For the pcm sense?
 
whats happening when the jeep dies? use the mt2500 and look at the data when it dies. see if it disconnects from the pcm. and if it starts dieing and you turn the switch off will it start running again?
 
When the Jeep dies the dash gauges freeze. The blower stays blowing. Turning the key on and off the dash is unresponsive the fuel pump never primes. Prettyuch nothing but the tape deck resets. And the vehicle won't start. The blower/mode must be switched to off before it will start again.
I can switch between it dying and keeping it run via the mode switch or the brake pedal. Either way I have to be fast it happens within a second.
That's what I was doing prior to the Jeep only wanting to run on fan speed 4. Switching the fan speed with Mode switch OFF the space between 2 and 3 caused the motor to stumble. When I held the fanswitch between the 2 positions is when it killed everything and the Jeep began to only run on fan speed 4. the blower worked on all 4 speeds but the Jeep now only ran on speed 4. I took out the BMR and ran the fan and that's when I fried the thermofuse.
I didn't know I could adjust the alt with the 2500 I'll have to look. I know I can step up the IAC 100 at a time though.
 
Ok so I hooked up the 2500 just now. The reader prompts to turn the key on etc etc because it's not communicating with the PCM UNLESS a my foot is on the brake at any fan setting or mode setting. OR the fan setting is on 4 and mode off.
I have a few more codes now but maybe from testing and starting without stuff plugged in but I'll list them. For my reference and yours.
Transcodes
P1694 CCd message from JTEC failure
P0122 throttle position sensor
P1745 shift Sol A shorted high
P1749 TCC Sol C shorted high
Engine codes
P0505 IAC motor circuits shorted
P0700 trans fault present
P0443 evap/purge Sol circuit open/short

With the Jeep idling looking at the 2500 data there's a line A/C request . It keeps switching from OFF / Allowed. If I apply the brake it stays on OFF.
 
I also found when moving the plug on the back of the FAN control the Jeep started running on all fan speeds despite the BMR missing. So I think I solved the Jeep only running on speed 4 issue. It also doesn't act funny anymore when stopping. the switch between 2and 3. I simply bent the tabs a bit in the control panel side and closed the connection on the plug a bit more. Can someone check their voltage s on their brake switch please. Curious what wht/pnk should have. And what it is with switch opened closed
 
Automechnic077 said:
I also found when moving the plug on the back of the FAN control the Jeep started running on all fan speeds despite the BMR missing. So I think I solved the Jeep only running on speed 4 issue. It also doesn't act funny anymore when stopping. the switch between 2and 3. I simply bent the tabs a bit in the control panel side and closed the connection on the plug a bit more. Can someone check their voltage s on their brake switch please. Curious what wht/pnk should have. And what it is with switch opened closed
Click to expand...

May help {?}

BrakeLampSwitch.jpg

.
Brake%20Lamp%20Switch%20Tests.jpg
 
Thanks Sidewinder, I have found a copy of the FSM for my 99 on the interwebs it's AWESOME! Just click and click and find whatever you like. I don't believe there is voltages printed on the schematic though? I didn't know what alot of the charectors meant until I downloaded the FSM So I may be missing something. I see the JB sends out a DB/WHT through the SLS then it comes out WHT/PNK So I guess it comes out hot and should be hot and close to 12v all the time. I have a hard time nderstanding which way the voltage travels in these schematics. For instance I thought the 12v was coming out of the PCM all this time. But Now after loooking further it actually comes from the JB through vaarious things than into the PCM.
I think I need a few gallons of gas and a road flare to be honest.

The switch operates as it should. The jeep does not. I had no choice but to drive it to work today. Everything seems great when the brake switch is setting in the cupholder! minus no brake lights
 
Last edited:
I ordered one yesterday from a company in Davie Fl. I included my VIN, mileage and the Number off the current PCM. Hopefully they match me up with the right one. I feel competent enough that I've checked every ground, every possible wire. If the PCM doesn't fix it at least I can return it and recoop most of my money back and try some more.
My PCM I currently have in the jeep is a 493AD It was the PCM that came with the jeep when I bought it and didn't have this issue.
 
I am almost positive it does, I don't have the jeep accessible at the moment. But I do recall seeing the Green screw top lid for the Evap and couldnt figure out what it was for. Don't tell me this could be the issue ;)
 
Automechnic077 said:
I am almost positive it does, I don't have the jeep accessible at the moment. But I do recall seeing the Green screw top lid for the Evap and couldnt figure out what it was for. Don't tell me this could be the issue ;)
Click to expand...

That green cap is a test port for the duty cycle evap canister purge solenoid system. The LDP will be next to the AC Accumulator, between it and the right inner fender.

LDP.jpg

.
I doubt if the LDP has anything to do with your problem, but I do think you said when you installed a starter it arced. That may have smoked your PCM.
 
It worked! The new rebuilt PCM worked! I have the smoothest idle ever, no more IAC short no more engine light! Ac brakes, heat. I haven't driven anywhere because the dash is still a mess and the air box is not bolted down but it works!
Thanks everybody for their time and patience I hope I can give back someday what was given to me.
Yes I have the LDP system and a clicky evap solenoid it's a constant click click click is it supposed to? I've never heard it before
 
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