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Discussion Starter #1
problem i had,
all of a sudden car ran hot in traffic the other day
went into limp mode,
no signs of problems before hand,
no codes being thrown, other than P420 cat converter which i dont think is related
took it to my mechanic turns out rad fan wasnt coming on,
he checked relays,
relays were fine but stated , they werent getting signal to turn on the fan,
he states bad pcm not giving the signal.
before i go out and blow $500-$900 on a pcm
(dealer price: $700 for the part -$100 Install-$80 to flash)
online search can get PCM's for about $500, but needs to be flashed which means a tow to dealer to flash, as wont start with a blank pcm.
would like to check other possibilities
anyone know how i can check the relays myself?
must be a temp sensor somewhere that tells the pcm to turn the fan on, where and how do i check that?
ideas for bypassing the relay/sensor and installing my own?
even if its a manual switch i can turn on when in traffic or running hot.
 

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One quick test would be to turn on the AC. This should turn on the fan regardless of engine temp. When I get home I'll check the factory service manual.
 

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Ok, maybe turning on the AC may not activate the fans, according to the FSM, the AC head pressure sensor acts as an input to turning them on. In the winter, the AC pressure may not go high enough to activate the fans.

Radiator fan operation is controlled by the Totally Integrated Power Module (TIPM), with inputs from the engine coolant temperature sensor, continuously variable transmission (CVT) oil temperature, and A/C head pressure. The (TIPM) turns on the fan through either the high or low speed fan relay. The PCM provides a ground to the relay's control circuit. The fan relays are located in the (TIPM) . Refer to the label beneath the (TIPM) cover for location of fan relays.
Here is the trouble check list (this was in a chart format):

RADIATOR FAN WILL NOT OPERATE, GAUGE READING HIGH OR HOT
1. Fan motor defective.
1. Refer to appropriate Powertrain Diagnostic Procedures manual for operation of the scan tool. Repair as necessary.

2. Fan relay, powertrain control module (PCM) or engine coolant temperature sensor defective.
2. Refer to appropriate Powertrain Diagnostic Procedures manual for operation of the scan tool. Repair as necessary.

3. Blown fuse in power distribution center (PDC).
3. Determine cause for blown fuse and repair as necessary.
Fuse 33 appears to be the power to the relays and Fuse 15 (50A) is power to the fans (actually power to blade 30 of the relay, ie the high current feed). The TIPM simply provides ground to terminal 86 of the relays (standard bosch relay terminal numbering where 85 is power to energize relay, 86 grounds it and pins (blades really) 30 and 87 carry the high current load when the relay is energized.

See if you can ground terminal 86 and trip the fans on. You might be able to wrap some thin wire around the top of the terminal, then plug relay back in. Then ground your test wire. Thin wire will be fine as this is just the relay load (probably only a few milliamps)

Here's a diagram of a typical bosch style relay, only pretend the lights are your fans

 

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Discussion Starter #5
Thanks T,
Will see what I can find tomorrow,
Or will have to wait till I get dig in and see what's going on, will let you know the outcome.
 

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If it was me, I would bring it to the dealer. Unfortunately this is the only scenario that justify's bypassing the local mechanic in the diagnostic work. Since the PCM has proprietary programming and diagnostic tools, that only Jeep and Chrysler have access too, this is the only way that the PCM can be ruled at fault.

I speak from personal experience. Last year my Liberty suffered from a intermittent no crank condition. All signs pointed to the PCM, including my local mechanics diagnostics. However there was no way to confirm.

So we bring it down to our local dealer and it took them 4 weeks to diagnose the root cause. The fault was a broken wire going from the gauge cluster to the PCM.

One thing to realize about buying a PCM from a vendor. They are not a guaranteed fix. They are assuming you have correctly determined the issue correctly and it needs a PCM. You may spend the money on the part and programming and find out that you have another issue entirely and most of them are non refundable.

I know that I was ready to replace the PCM on my own, but I knew it was a possible bad move. In the end I let the dealer figure it out on their dime knowing that anything that they replaced and the problem was still occurring, they were going to eat the cost.

Here's a video I created early on in the diag phase while it was dead in the garage at my house.

 

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I just had the relays, and wiring to the cooling fan, replaced. Wires were corroded on the inside, corrosion around the copper under the insulation on the wire. Could not see it till wire was cut. The fan was intermittent, sometimes worked, sometimes not.
 

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I hear what you're saying 99, but by grounding the relay (two relays actually, one for low speed and one for high speed) you determine where the problem could be located. The PCM simply grounds the relays based on the inputs described in my previous post. If the fans turn on after grounding them then it's likely an issue in the ground wiring from the relays to the PCM or the PCM itself.

The second part of this is if the fans do work after grounding them, he could install a switch to ground the relays on demand, allowing to put the repair off until funds or time is available.

Terasec, are there any check engine codes?
 

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Discussion Starter #9 (Edited)
Fuse 33 appears to be the power to the relays and Fuse 15 (50A) is power to the fans (actually power to blade 30 of the relay, ie the high current feed). The TIPM simply provides ground to terminal 86 of the relays (standard bosch relay terminal numbering where 85 is power to energize relay, 86 grounds it and pins (blades really) 30 and 87 carry the high current load when the relay is energized.

quick check
fuse 33 is fine,
Fuse 15 also has power
now to track down the relays,
are they located in that box next to rad by the drivers side headlight?
looks like a pain to work in there

i also tried running in 4lo/4x4 and fans still did not come on


no codes on self on/offx3 diagnostics
only code coming up through scan is p420 cat converter
 

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The relays should be in the fuse box under the hood. The underside of the cover should point out what's what.
 

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Discussion Starter #11 (Edited)
Relays are in a seperate panel near the drivers side headlight,
5 identical relays, just checked them all have power and are grounded,
I didn't check all terminals on the relays, just main power and ground


There is an old label on the side which may have indicated which relay is for what, but too faded, can't read it
 

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Huh, that's odd because the FSM says they (the fan relays) are in the main fuse box. Anyway, pull fuse 15 and see which two lose power, then you'll have your two fan relays. There should also be a lack of continuity to ground on the one terminal (where 86 would be on the relay diagram below).

One other thing you could do is unplug the relay and using heavy gauge wire, jumper between the two sockets that would be #30 and #87, see if the fans turn on.
 

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Discussion Starter #13
Will check it later,
Trying to scrounge up scrap wire to use as a jumper,
Most of my stuff, tools, wire, etc I keep in pa.
Wifes iphone charge will make for a costly scrap wire
 

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Discussion Starter #14 (Edited)
I narrowed it down to 1 relay,
Where blade 30 is getting no juice,
Yet blade 86 is getting juice.
Blade 30 gets gets its juice from fuse#15
Fuse 15 has juice, so problem between fuse #15 and relay blade 30?
I just hard wired blade 30 to fuse 15 and fans came on with car off.
 

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Discussion Starter #15
where i stand,
blade 30 of relay is not getting power,
problem is either fuse box not sending power to relay,
or relay box is not transferring power to relay.
if problem is fuse box,
$700 for box, needs to be flashed, so quite difficult to do it myself and tow it to dealer to flash,
relay box is integrated into wiring harness, not a seperate part(^$$%^)
$383 for harness, plus labor which is estimated at +3 hrs,
right now have blade 30, wired where if it overheats i can connect directly to fuse to turn on fan.
when i get a chance will get dealer to accurately diagnose the problem,
and take it from there
 

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Good luck, and let us know how it turns out.

Mine was very intermittent, which makes it really tough, and over $400 so far from the dealer. And hard to tell if it always runs now, or if I still have a problem sometimes.
 

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Discussion Starter #17
while looking around, couldnt find any corroded wires, or loose wires,
but did see quite a few exposed wires with nicks and and scratches where internal wires are exposed,
i recommend others to get inside and look at their wires, wrap any exposed wires in either wire wrap or electrical tape.
even my o2 sensor wire is frayed that needs to be wrapped.
exposed faulty wires seems to be a vulnerable weak point in the pat
 

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Can anyone tell me which of the relays belongs to the AC? I see the box, and like someone else mentioned, the label on the side is illegibly faded. Trying to get my AC compressor to turn on so that I can diagnose the system/find leak and take it from there... thanks!
 
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