Question about 2003 Jeep Grand Cherokee

2 Answers

Fan does not run

We are being told that it is the PCM that is causing the fan not to work. Can we replace the PCM with a remanufactured one?


Posted by djvanh on

  • djvanh Aug 23, 2008

    Thanks for your interest and input. We took it to a local mechanic's garage. He checked it out and said it was the PCM and advised taking it to our dealer to have it replaced. We took it to the local Jeep Dealer who put it through the diagnostic computer and charged us another $120 to say there is nothing wrong with it. One week later we're still having the same problem - overheating - and the fan doesn't run. It runs some of the time, but not all of the time. We don't have a service manual, but are thinking of getting one with the problems we're having with this car. It has about 78K miles on it. We're in Sioux Falls, SD. It was a Jeep Certified car and has just a few mi left on the warranty. Tonight it's sitting back at the Jeep Service Garage, waiting for them to look at it Monday morning. Thanks again.



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I had this similar prob it turned out to be the fan relay. It is located under the front right head light, you have to cut a hole to get to it. The relay was $48.00 at an auto parts store. If you need I can send pictures to show how I cut it and patched the hole.

Posted on Nov 08, 2009



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I guess I better ask you a couple of ?'s before going any further here - as I'm not getting back any feedback at all as to what I posted previously.

No past history - no past to present attempted fixes - no troubleshooting feedback.....

The reason I say this is because now you are saying > We are being told that it is the PCM that is causing the fan not to work.

This has me asking - WHO is telling you that the Powertrain Control Module is supposedly bad? By WHO I mean - Jeep dealership - auto repair garage - your friend - who?

I need to know what steps you took to get to this new revelation point - as to the fan supposedly not working?

Please be very specific, and not just a 1 or 2 line reply - as that won't help me pinpoint the problem at all. After all - you have the SUV there (wherever you are located state/city wise), and I don't.

Also - do you have the/a service manual (Haynes or Chilton Auto Manual for your year & make Jeep)?

When I get your feedback we can proceed forward.



Posted on Aug 13, 2008

  • 1 more comment 
  • Anonymous Aug 23, 2008


    Any response or reply back here??

    I'm not getting any feedback at all here. I sure wish people posting
    here would feedback to the Experts here as how else will we know what
    is happening with your problem??



  • Anonymous Aug 24, 2008

    Now we're getting somewhere!

    Thanks for the updated feedback! Really helps me out, as now you are
    telling me that the Jeep is overheating as well. You never mentioned
    that part before and that part is new news to me.

    Btw - Those Jeep dealerships are something else, as they ripped off my
    sister to the tune of $500 on her 1988 Grand Cherokee Special as well,
    and never fixed the rough idle problem (dirty injectors is all it
    was!). I feel they are all out just to make as much repeat money on
    people as they can get away with, and then wind up fixing very little
    to boot! I strongly feel you are being ripped off by that dealership
    there as well. Esp when they try and charge you $120 for a supposed NO
    CODE, and do absolutely nothing! That is criminal....

    I still say it is very rare that the PCM is bad. Usually it's just a
    faulty (dirty or starting to go bad) Sensor or else it's a dirty
    connector with poor contacts.

    What you really need to do - like I did - is purchase a $40 OBDII Code
    reader with the newest generation CAN protocol (Control area Network).
    This Code Reader is very easy to use, very well made, and the User's
    Manual is very easy to follow and understand, and you don't have to be
    a rocket scientist to use it and fix your own car Sensor problems!!
    I've been doing it for years now and have saved bundles of money on
    otherwise gouged Sensor R&R repairs! Think about it?

    I bought mine from Harbor Freight Tools (HFT part # 94169). Then you
    can read and catch the bugger code(s) that keeps eluding everyone (if
    it indeed is an intermittent code).

    I still say it's either a bad T/S, or else possibly the Fan Relay
    Switch usually Jeep located under the front bumper just behind and
    under the headlight housing on the passenger side of your SUV. Pretty
    lame place to put it making it nearly impossible to check out

    If your T/S Sensor (usually located in the radiator body on the drivers
    side) is made of a thermal plastic body material (instead of a brass
    metal body) my suggestion would be to replace it first (cheaper of the
    2 possibilities) - that is if you can't measure out either/or one while
    still in circuit. It is most prone to failure, and several other car
    makers have "recalled" defective ones with the same identical fan
    problems as you have there.

    If jumpering, or shorting out the T/S Sensor connector wires going to
    the fan motor kicks on the fan with the engine up to full operating
    temp, then the T/S Sensor is bad (stuck OPEN) and it's causing the
    problem. Done deal - usually a $10-15 replacement part at Pepboys!

    If the fan still doesn't run with that T/S connector shorted to the fan
    with the engine at full operating temp, then the Fan Relay Switch needs
    to be jumpered as well to see if you are getting a good control signal
    voltage from the PCM to that Fan Relay Switch. A good PCM voltage
    signal means a BAD Fan Relay Switch or possible an OPEN wire in the
    wiring harness to the PCM. It happens!

    Unless the fan has a separate Over-temp Sensor that is stuck OPEN
    making it possibly bad as well - then the PCM can't be singled out to
    be bad at all. By that I mean - it's a $$COSTLY$$ "GUESS MISTAKE" if
    the PCM is indeed GOOD and not causing the problem.

    Everything else "has to be ruled out first"!

    I still can't believe you aren't getting a CHECK ENGINE Hard Engine
    Code with a Code Reader. Someone is snowing someone somewhere!!
    Hopefully your CHECK ENGINE light is connected and working OK??

    Because you said you have the warranty in force at this time, and they
    (illegally charged you $120 just to read the/any Hard Codes) I would
    contest that charge as being part of the warranty repair!

    I would also make sure they don't drag this out past the warranty
    period you have left there just so they can stick it to you repair wise!

    Stand your ground whatever you do!

    I would also look into getting a good Chilton Repair Manual that fully
    covers your Jeep. Try and stay away from the cheaper Haynes Repair
    book, as it doesn't cover as much - unlike the Chilton that includes
    related Trouble Codes in great detail.

    Keep me posted on what happens - appreciate it greatly.



  • Anonymous Aug 24, 2008

    PS: Forgot to include these related DTC
    Engine related Cooling Codes as possibilities that should be showing up
    on a Code Reader check.

    An * after a certain code means this is a strong possibility of what the problem may be:

    P0115 Engine Coolant Temp related

    P0116 Engine Coolant Temp related

    P0117 Engine Coolant Temp related

    P0118 Engine Coolant Temp related

    P0119* Engine Coolant Temp CKT Intermittent

    P0125 Coolant Temp related

    P0126* Coolant Temp Insufficient Stable Operation

    P0128 Coolant Temp related

    P0217* Engine Overtemp Condition

    P0480* Cooling Fan 1 Control Circuit

    P0481 Cooling Fan 2 Control Circuit

    P0482 Cooling Fan 3 Control Circuit

    P0483* Control Fan Rationality Check Malfunction

    P0484* Control Fan CKT Over Current

    P0485* Control Fan Power/Ground Circuit Malfunction

    P0493 Fan Speed related

    P0494 Fan Speed related

    P0495 Fan Speed related

    P0526* Fan Speed Sensor Circuit

    P0527* Fan Speed Sensor CKT Range/Performance

    P0528* Fan Speed Sensor Circuit No Signal

    P0529* Fan Speed Sensor CKT Intermittent

    P0606* PCM Processor Fault

    P0607* ? PCM related

    P0608* ? PCM related

    P0609* ? PCM related

    P0610* ? PCM related

    P0630* ? PCM related

    P0650* MIL Control Circuit Malfunction

    P0666* ? PCM related

    P0667* ? PCM related

    P0668* ? PCM related

    P0669* ? PCM related

    P0691* Fan 1 Control Circuit Low

    P0692* Fan 1 Control Circuit High

    P0693 Fan 2 Control Circuit Low

    P0694 Fan 2 Control Circuit High

    P0695 Fan 3 Control Circuit Low

    P0696 Fan 3 Control Circuit High



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NO ENGINE STATED, SO on exact answers. 4.0L or 4.7L ???
The engine cooling and HVAC rules govern this (computer tables and logic)
the service manual cover that,
did you SCAN the PCM at the failure then scan it again after, no?
did you know some cars run the fans parked to prevent overheat soak damage to the engine and trans? all have hood sticker warning telling you to stay way from fans, , until fully cooled engine or pull battery neg lug for safety. just saying that so you are safe fiddling all cars.

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Self preservation.
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her is what chapter 7 states
The pulse width modulated (PWM) radiator cooling
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PWM relay operation is controlled by the Powertrain
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the SM does not list all rule and tests for this device.

here more quotes from your missing book
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My answer:

I answered a similar ? at Yahoo Answers awhile back, and it solved that person's problem on their 1987 Jeep.

Though you weren't very specific as to your 2003 Jeep Grand Cherokee's problem by just saying the fan motor doesn't work, I'm taking it that we are talking about the "radiator fan motor" here.

You most likely have a two-fold problem going on with your radiator cooling fan.

Seeings a new fan motor didn't solve the original non-op problem we can definitely establish that the old fan being bad really wasn't bad at all and NOT the problem to start with.

As with any 12-volt DC automotive motor (whether for the radiator cooling fan, windshield wiper motor, interior passenger compartment cooling/circ fan, etc) a simple disconnected from the car's electrical system test should have been done 1st to make sure the old fan motor was really bad. Too late for that now though. I myself would have seriously doubted that a 6 year old fan motor would have been bad already.

If you had no recent engine or radiator related mechanical work done to the Jeep - as of late - then the problem may not even be a bad wiring harness connection, but you never know.

If all the radiator fan Temp related Sensors & Thermal Switch connectors are properly seated then we need to look at yet another possibility having eliminating a wiring connector type problem.

On most radiators with an electric assist fan(s) there is also an electric Thermo Sense switch (TS) mounted on the radiator itself that has to be working properly otherwise this fan switch could stick in the CLOSED position (set point usually 190 degrees F) leaving the fan to run all the time while the engine is running. Make sure it is connected as to the wiring connector, as I've seen this connection get pulled apart from other engine related work being done or else from a bad connector itself.

If this TS goes bad and someone disconnects it so as to stop the fan from running all the time - then it may look like the fan itself is bad when it really isn't.

On the other hand this TS switch could actually stick in the OPEN position (though this is very rare with this type of Thermal switch), and then the fan wouldn't run at all, and the engine would probably run HOTTER then normal as a dead giveaway. If your engine is running HOTTER then normal I would go directly to this TS and check it for proper operation. It's usually mounted on the radiator fan bracket nearest the radiator with a separate 2-wire wiring connector.

If it's working properly - when the ignition is turned off - the fan should still turn off as it is usually controlled by a timed RELAY circuit as a failsafe. Does it??

Hopefully you don't have any engine cooling problems to start with, but if you do follow the guidelines below:

If the engine thermostat is sticking CLOSED, or indeed stuck CLOSED, that could also cause the fan to run excessively. Running plain water in the engine and not proper 50/50 antifreeze/coolant mix can also cause the engine to run much hotter then normal and thus adds to running the radiator fan more frequently then normal.

Excessive radiator fan running leads to just one thing, and that is worn out bearings. Some of these fans aren't made that good to begin with!

If the fan is indeed 'tired' or has a tendency to try and freeze up there should be safeguards to prevent wiring from burning up.

Most radiators have 2 thermo-switches (TS), one being an ambient radiator surface mounted TS, and the other one being an internal (screwed into) radiator mounted TS. There might even be a 3rd fan TS that is clipped directly to the fan motor case itself to sense an over-temp situation like that from the fan bearings freezing and the fan itself running hotter then normal. Just depends on car maker design.

There is also a TIMER RELAY module incorporated in all CA equipped cars as part of the SMOG packaging for cars sold here in this state. Reason for that is to reset the pre-warm circuit properly when restarting the car back up after shorter run and stop trips. If this relay is bad it could cause the fan to run on longer then normal after shutting off the vehicle, thus causing undue wear and tear on the fan motor also. I used to think it also helped to clear out any fuel fumes from under the hood after running the engine, but could never prove it or have it verified by my own minivan maker when I owned a minivan??

NEVER DRIVE THE JEEP WITHOUT THE FAN MOTOR BEING CONNECTED!! You will surely damage something you don't want to!!!

To check the radiator fan circuit do the following:

I would first disconnect the battery from the circuit, and do any resistive type DVM meter checks first (unless you are unsure of how to do them), and then do the following checks below to check out the fan motor and related sensors/switches with power reconnected. If you have a lot of MEMORY type devices onboard your Jeep (Stereo, GPS, etc) you might want to use a simple 12-volt TEST LIGHT or again a good DVM to trace for a good ~12-volt battery voltage at point-to-point connectors instead, so as not to lose those memory settings.

First check the wiring leading to and from the fan motor itself and the TS (1 or possibly 2) connectors to make sure they are snapped together fully and making good connections. Also check the GROUND WIRE coming off the fan motor connector - as if this ground point is dirty or corroded causing a bad ground return path then the fan motor will appear to be dead as well.

Next check the fan itself for free-play. Is it turning freely or is it very tight or hard to spin?? If so - you have a bad fan and it's time to replace it NOW! (In your case it doesn't appear to be a bad fad fan motor at all.)

If you are handy with a digital volt meter (DVM) connect it in DC series with the fan motor and while running the Jeep measure the current and compare it to a new fan's rating. If it's excessive then the fan motor is on it's way out. Time to replace. (Skip this part too, as your fan is known good.)

VERY IMPORTANT STEP HERE - Also check those 1 or 2 TS switches to make sure they are in the OPEN setting with a COLD engine/radiator. CHECK AGAIN to make sure they CLOSE at the proper engine temp as well. If they don't close at or near 190 degrees F then one or the other (if there are 2 or more in your system) may be bad, and that may very well be your only problem.

If Jeep has added a FUSE or FUSIBLE LINK to the fan circuit make sure you check that part also. It's doubtful though, as the fan circuit is fairly simple by design. A Timer Relay type Switch would be downstream of the/any TS switch(es) by design as well, so I would place my money 1st on a bad TS switch, or a possible bad ground connection 2nd.

Does not appear to be anything else that excessive as it looks to just be isolated to the radiator fan circuit itself.

Hope this helps you out to troubleshoot the problem. Feel free to email me if you still have further ??'s.



posted by djvanh on Aug 13, 2008

We are being told that it is the PCM that is causing the fan not to work. Can we replace the PCM with a remanufactured one?



I guess I better ask you a couple of ?'s before going any further here - as I'm not getting back any feedback at all as to what I posted previously.

No past history - no past to present attempted fixes - no troubleshooting feedback.....

The reason I say this is because now you are saying > We are being told that it is the PCM that is causing the fan not to work.

This has me asking - WHO is telling you that the Powertrain Control Module is supposedly bad? By WHO I mean - Jeep dealership - auto repair garage - your friend - who?

I need to know what steps you took to get to this new revelation point - as to the fan supposedly not working?

Please be very specific, and not just a 1 or 2 line reply - as that won't help me pinpoint the problem at all. After all - you have the SUV there (wherever you are located state/city wise), and I don't.

Also - do you have the/a service manual (Haynes or Chilton Auto Manual for your year & make Jeep)?

When I get your feedback we can proceed forward.



1 - Highly degreed in Electronics first of all.

2 - Worked for 2 SEARS AUTOMOTIVE STORES, one on the East Coast and the other one still being the largest SEARS AUTO in CHICAGO at 6-corners. I specialized in troubleshooting all auto electrical problems - including battery testing and charging system testing and repair. Graduate of DeVry in Chicago also!

3 - Troubleshooted, repaired, and replaced many water pumps, thermostats, fans, TS units, and radiators on all types of vehicles and makes and models. I hate those stupid internal water pumps on many of the *** Honda and similar autos as that is the dumbest design I've ever seen! Stay away from buying one of these headaches!! Timing belts (non-metal type) are just as bad!

Aug 11, 2008 | 1999 Plymouth Grand Voyager

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