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Radiator Fan Override Switch (The Easy Way)

Update: PCM isn't turning on the E-fan either. Could this be caused by weak voltage in the blue/white wire ST-RUN source in the big loom? I saw some replies referencing the one in the smaller loom correcting their problem. I'll check things out with the multimeter later and hope to get to the bottom of this.
 
BUT...per beasticles' diagram, Pin 30 and 87 are actually switched around. You confirmed this is correct. Is this mixed up in your original post? Perhaps all I need to do is switch those around? I currently have the DB/PK wire + switch ground spliced to 87. The fan does switch on and no CEL when I do turn the switch to ON.

Honestly, it doesn't matter. The relay is just making and breaking the connection between the ground and the factory relay. It doesn't care what's connected to either end. If this was a more complex circuit where you were using both the 87 & 87a pins, then it could matter. Beasticles labeled it correctly per the way I drew it, but now that you've pointed it out, I see that my drawing doesn't exactly match the directions. I just cut and pasted the relay symbol from the FSM. Relays are typically drawn with the 12V+ connected to the COM terminal and the device being activated connected to either the NC or NO terminal. I guess I should have flip-flopped the switch symbol inside the new relay since we are switching a ground.

Update: PCM isn't turning on the E-fan either. Could this be caused by weak voltage in the blue/white wire ST-RUN source in the big loom? I saw some replies referencing the one in the smaller loom correcting their problem. I'll check things out with the multimeter later and hope to get to the bottom of this.

Think you're on the right track here. It seems as if the coil isn't being energized in your new relay which would indicate either a bad connection somewhere between the PCM and Pin 85, or (more likely) insufficient voltage being supplied to Pin 86. Test that DB/WT wire and make sure it's giving you 12V+. The relay needs at least 8V to activate.

You could also try disconnecting the PCM from Pin 85 and applying a ground directly to the pin. You should hear the new relay "click" if it has the necessary voltage and is activating properly.
 
Minor point - you don't actually need to disconnect the ECU from that pin to do that test. That pin contains what's technically known as a ground-side switch, grounding the wire with the ECU still connected won't break anything, though it may cause a DTC for a shorted or inoperative fan relay circuit. Unplugging the relay or interrupting that wire with the jeep turned on will result in a similar code of some sort anyways, so you aren't going to really lose anything either way.
 
Minor point - you don't actually need to disconnect the ECU from that pin to do that test. That pin contains what's technically known as a ground-side switch, grounding the wire with the ECU still connected won't break anything, though it may cause a DTC for a shorted or inoperative fan relay circuit. Unplugging the relay or interrupting that wire with the jeep turned on will result in a similar code of some sort anyways, so you aren't going to really lose anything either way.

Good info! Wasn't sure what would happen, just thought it might not be good. Thanks for the technical explanation.
 
Okay guys I got this fixed the other day and wanted to update. When I tested the blue/white wire out of the big loom, it had a solid 12.4 volts with the ignition in the RUN position. Pretty interesting. But when I ran a jumper wire direct from the battery to pin 86, it worked perfectly. I then cut into the smaller loom and found that blue/white wire and hooked it up, and it works great now. Thanks for the help, fantastic mod! :)
 
Just did this mod today and all was good except the fan wouldn't come on with the ac. Turns out the dark blue/Wht wire I spliced into goes completely dead as soon as the ac is activated.

Took an annoying amount of time to troubleshoot. Still not sure what that wire runs.
 
Fyrfytr thank you again. I wired this up today and it worked like a charm...until I switched on the AC. Triggered the CEL immediately. I see on page 11 of this thread someone posted about putting a resistor in the switched line. You didn't run into this problem yourself? I followed the diagram I supplemented with relay pin numbers to a tee. Any thoughts would be much appreciated.
 
Reading some of the replies, it looks like a great idea to leave well enough alone and let the Jeep operate as the factory intended.
 
I found this guy who was having a similar issue and he skipped the DB/WT switched wire and connected straight to the positive terminal of the battery:

I disconnected the positive going to the relay and connected it directly to the battery positive. The "CHECK ENGINE" has gone out. I suspected the PCM didn't like the 12 volts coming and going. If it stays off for the next few days, a week, I'll report back and probably create a new thread on how to install a electric fan on 1997+ XJ bypass switch
http://naxja.org/forum/showthread.php?t=1025399

I'll give it a go and report back
 
This worked to cure the CEL for me! Ran a lime direct to positive battery terminal instead of tapping into DB/WT wire like I had it. Now no CEL is triggered with AC on and the fan switch works great. Thanks fyrfytr!

This worked on a 2000 XJ so I assume this is the trick for '00 and '01 model years.
 
Reading some of the replies, it looks like a great idea to leave well enough alone and let the Jeep operate as the factory intended.

No one is going to make you do it to your Jeep, but judging by the fact that this thread is 13 pages long and has over 33,500 views... I think there's some interest in doing this mod. :spin1:
 
This worked to cure the CEL for me! Ran a lime direct to positive battery terminal instead of tapping into DB/WT wire like I had it. Now no CEL is triggered with AC on and the fan switch works great. Thanks fyrfytr!

This worked on a 2000 XJ so I assume this is the trick for '00 and '01 model years.

Glad you got it figured out. I'm not sure if there is a variance with the '00 & '01 models (very well may be), but I know that it seems finding the correct switched ignition wire seems to be the trickiest part of this mod. The DB/WT in the small loom seems to be a more reliable choice than hoping you get the right one in the big loom. That being said, there's no major issue with running it directly to the battery, you just have to remember to turn it off.
 
Glad you got it figured out. I'm not sure if there is a variance with the '00 & '01 models (very well may be), but I know that it seems finding the correct switched ignition wire seems to be the trickiest part of this mod. The DB/WT in the small loom seems to be a more reliable choice than hoping you get the right one in the big loom. That being said, there's no major issue with running it directly to the battery, you just have to remember to turn it off.

After actually re-reading some of these posts this morning (for the umpteenth time), I realized that PocketsEmpty had the exact same issue and exact same cure.

I don't know if NAXJA allows it, but if you could update your first/original post with this information it may help others. Also, I updated the annotated wiring schematic to hopefully help others. Of all of the mods i have done, this is actually really easy if you go into it with fyrfytr's guidance and the wiring schematic.

Tools I used were as follows (I did not solder anything but if you are more advanced/have more time that would be a good idea):

> roll of 18 gauge wire (I bought a 40' roll and used about 70% of it for this project - includes waste)

> wire stripping/crimping tool

> electrical tape

> package of assorted electrical connectors that must include at least 4 female receptacle type connectors (wide enough to slide onto relay pins) and 3 U shaped terminals or O shaped type terminals (for ground wires)

> one or two vampire/quick-splice connectors (only need one if you are tying the ST-RN source from the positive battery terminal directly to the relay, the quick-splice will be used to connect the DB/PK wire to the wire running from the switch to the relay)

>convertible top relay (this is sold at a lot of auto stores under different part names and numbers - this one from Advanced Auto worked for me and I saved 30% by buying online and picking up in the store - Part #R3177P, Brand: BWD, http://shop.advanceautoparts.com/p/...T-_-Trans-_-Confirmation-_-General#fragment-2)

> two-way switch (this is the one I bought but any two-way switch will do: http://shop.advanceautoparts.com/p/...utm_campaign=confirmation&utm_content=general)

Here is the updated schematic:

14844661760_080a893f70_b.jpg
 
Don't think I can edit my old post, the edit option goes away rather quickly. Regardless, the info provided there is still working for me years later so I'm not really inclined to change it anyway. Your schematic is nice, I like the color coding and relay numbering. I'm not sure I agree with your suggestion that some model years may need to tap directly to the positive battery terminal either, especially '99 as that is my model year. I'd agree that you can tap directly to the positive battery terminal and think it has been discussed somewhere earlier in the thread. I'm pretty sure this mod had been done successfully with all 97+ model years by now. If there is any variance regarding model years, I would think it would only apply to '00 & '01 due to their different electronics.

If I could change something regarding my original post, it would be that I would suggest using a "Posi-tap" versus the Scotch Lock Quick Splice pictured in my write up. More secure, less destructive, and an overall better product.
 
Don't think I can edit my old post, the edit option goes away rather quickly. Regardless, the info provided there is still working for me years later so I'm not really inclined to change it anyway. Your schematic is nice, I like the color coding and relay numbering. I'm not sure I agree with your suggestion that some model years may need to tap directly to the positive battery terminal either, especially '99 as that is my model year. I'd agree that you can tap directly to the positive battery terminal and think it has been discussed somewhere earlier in the thread. I'm pretty sure this mod had been done successfully with all 97+ model years by now. If there is any variance regarding model years, I would think it would only apply to '00 & '01 due to their different electronics.

If I could change something regarding my original post, it would be that I would suggest using a "Posi-tap" versus the Scotch Lock Quick Splice pictured in my write up. More secure, less destructive, and an overall better product.

When I have time, I'll change that note in the diagram about the '99 models to reflect that on a 2000 the direct battery line may be needed so as not to confuse anyone. Thanks again for taking the time to post this up. I wish my setup looked as good as yours but this mod is working without a CEL so I am happy. :cheers:
 
(apologies to fyrfytr for cluttering up the thread)
Okay, poking around with the meter, doing some googling. The light blue wire isn't ground, it's power. Ground is black, and unswitched. The relay in the PDC, when energized, puts 12V on the blue wire, fan runs. Taking an educated guess here, but is this how you actually wired it up, Charles? (and sure enough, the PCM doesn't monitor the fan, just the control ckt)

FanPCMBypassed.jpg


Switch off, stock power wire connected to 87a (NC) contact, wire from fan connected to 30, fan runs only when PDC energizes.
Switch on, battery power on 87, fan on 30, stock power wire held open, fan runs constantly.

Have I got it right?

Just did this on my '96 XJ & it Works Great. No Codes.
Wired power to Accessory Terminal @ Fuze Block.
Pos. Wire on my Fan is GRN Not Blue.
Now I Can turn On the Fan when Wheelin in the Summer.
Thanx 4 the Diagram.
UncleSarge58
 
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