Jeep pcm

Asked by Jul 27, 2017 at 08:48 AM about the 2002 Jeep Grand Cherokee Limited 4WD

Question type: Maintenance & Repair

If I get a Pcm from the junk yard will it
need to be reprogramed

99 Answers


Yes, the only way around it is to find one with the exact same numbers as your stock PCM.

what if I find one with The same Vin (mine is vin N)

Also will my key need reprogramed


Vin N is just an engine designation not a calabration code, the numbers on the computers need too match. An 02 should still have a separate BCM so no you won't need to recode the keys. Why do you suspect the main processor is the problem?

Cause is Code p0601. Are you sure I won't have to recode keys if I find a matching computer

I just don't know if it really needs fixed, engine light is on but I've never had any problems or anything with it


I just checked with my Jeep guy and he says that you should not have to recode the keys either, that code is stored in the BCM not the PCM. Have you tried getting a re-manufactured unit? HTH

No. I just don't know the seriousness of the code as it runs good

And if I get one from the junk yard will are the numbers such as S/N number and stuff all need to match my Pcm or just the Part number off mine


Just the numbers off the PCM's need too match. The PCM's numbers also contain the calabration code for you year make and model, so if the numbers don't match the calibrations won't be correct, it may or may not run if the wrong PCM is installed, but if it does run it won't pass any kind of inspection as the emissions will be way off.

So all the numbers off the pcm, Not just the part number need to match correct ?

Just doing some research on the subject. I'm convinced there nothing wrong with mine, it runs good. I'm thinking previous owner unplugged something while it was running so it threw the code. I've had no problems with it. Neither did the previous owner.


It may seem like it is running just fine, but what it is doing with that code the memory is not active so the computer needs to relearn the vehicle everytime it is shut down and restarted, it's hard to say how long it will last this way but if you have inspections before it can be relicensed it will not pass, but if your state doesn't do that then go ahead and run it till it fails completely.

I do not believe ohio does inspections. But it has 220.000k miles (it's my first car) so I figured if the Pcm does have a real problem it will probably last along as the rest of the cars life as the cars old. I'll be getting a new car in a year or so .

So with this code should I be questioning the reliability of the vehicle? Would it be ok driving long distance with this code

Where can I find calibration code on my Jeep


If you have a Jeep scan tool you can find it in the system's specifications menu, but only with a Jeep scanner, no one else's scanners can access this information. There were a few Jeeps that had a sticker on the front core support but I think they dropped that in 2000.

But if I find a Pcm that the numbers all matchy current is should work correct


If the numbers match it should work, unless something is wrong with the replacement, that's what is scary about used electronics.

I noticed there's a few different numbers on the Pcm what if only the part number matches will it still work .

So the real question is if I go to the junk yard and find a Pcm from the same Jeep as mine with matching Pcm part number as the one on mine will it work?


Yes, as long as it is fully operational.

So I got in my Jeep and no power at all no lights radio gauges start. Nothing. Hooked battery jumper to it and it works fine what could be the problem

But it just started fine about an hour before that, also I know the battery had plenty of charge because it was still sparking when I unplugged it


Corroded battery terminals or a bad battery,for some reason Jeeps are hard on normal lead acid batteries, I ran gel cell battery in mine, they last about 5 years.

Battery terminals are not corroded. So I guess it's the battery then it's a carquest one . I have no idea how old

I also forgot to mention something so this is how it went it was parked overnight. Then started and parked in driveway then about an hour later I got in it and the lights work bc I opened glovebox and the light was on but then I put key in ignition to roll windows up and nothing no power . Like a mysterious drain somewhere


A shorted cell in a battery will act like that, enough power to run minimal lights but any high demand and nothing.

Thanks .So new battery is my best bet ?


Well have it tested first, then if it tests bad repalce it, this Jeep is old enough that you won't have to worry about messing up the computers when the battery is removed.

I believe it is good because I had it on charge overnight and it was fully charged reading 12.7 volts while the vehicle was not running


It's not the voltage but the ability of the battery to carry a load that determines if it is a pass or a fail, it can read perfect textbook voltage but apply a load and see where is goes.

It's gotten even stranger. Now battery voltage is 12.2 go to start lights come on it clicks battery is dead all of the sudden. Then have to jump start it runs fine then when I shut it off then restart it, it almost dies dropping to low rpm for a second or so battery voltage also drops to for a sec as well and thenafter a sec of almost dying battery voltage gos up and rpms go to normal ?


Battery voltage is still too low, did you have it tested?

Not yet going to tomorrow just looking at other possibities.

So I used a test light and car has a draw somewhere. Haven't found it yet but the light dimmed on one fuse could that be it ?


The test light should only glow slightly due to the parasitic draw, this sounds like you have more than one draw heavy enough to kill a battery in a short period of time. Remove the fuses one at a time until the test light goes out or just glows, then find what is on that circuit and repair or replace the malfunctioning componets, then start replacing fuses one at a time, if the test light comes back on when you reinstall a fuse then do the same as previously on the other circuit, do this until you only have just a slight glow or no light at all. Time consuming I know.


Forgot to mention, electrically disconnect the alternator before continuing on, a bad diode can cause a draw also and a lot of test benches won't test diode direction.

Would the light slightly glow for Pcm and alarm radio memory etc ?

I mean like would the test light dim alittlw for every car or is it supposed to be no glow at all


Yes anything with a KAM circuit the test lamp will just glow, but not a bright light.

What is jb power ? It was in slot 15 in the fuse box the light got significantly dimmer after the jb fuse was unplugged


It is one of the main power supplies that feed the junction box, and there a number of systems that feed from there including door modules. So I would plug that one back in and redirect to the junction block and remove the smaller fuses and see if you can track it down by breaking the circuits down to individual systems instead of the systems mains.

It's strange . Battery all electronics are fine until I crank over then it clicks dead . Maybe try cleaning terminals and stuff first ?


Earlier you stated that they were not corroded, Jeeps seem to have a problem with black corrosion, not the white stuff that you tend to see on a terminal end but this stuff get in between the battery post and the terminal clamp and really mess things up, both the terminal and the battery posts need to be shiny clean, then just hope that the corrosion hasn't got into the main cables.

I just took a quick lookbefore. But taking a deeper look the terminal cables are dull looking. I'm gonna clean them both up

I don't see how corrosion could all the sudden make the battery dead as soon as u crank


Corrosion is a terrible conductor, sometimes it may let voltage through but amperage is not going to happen.

It's very strange. The battery stays charged fine for days while sitting everything's normal until u try to crank it over . Every once in awhile when u try to crank it over it drains the battery . But the battery stays charged no drain or anything till u try to start it

That problem seems to be fixed Would you think that the Jeep would run cooler if it had the correct power steering fluid ? Since the fan is powered by the pressure from power steering pump if the wrong fluid is not giving enough pressure to power the fan it may not run full speed ?


I doubt it would have that much actual effect on the fan speed as the control valve would just open more to increase the flow to make the fan run faster no matter if the fluid was of a different blend as long as it was within the hydraulic specific oils. These Jeeps are really bad about getting the lower section of the condenser all banged up and the fins laid over, so look up under the front and check the fins for damage and also for dirt and bugs blocking the air flow.

What if the fluid dosent meant the specs for my Jeep? Ps . I have checked no damage or anything


It will loose it's viscosity in a much shorter period of time, flushing is the best option, but doing it the hard way, you can suck out the pump, put in the good stuff, start it cycle the steering lock to lock, and suck it out again, this should be repeated at a minimum of four times to get as much of the unspecified fluid out as possible. True some of the unspecified will remain but it will have been so diluted with specified that it's negative results will have little to no effect.

Thanks . I'm gonna drain it and put the right stuff in it because the pp whine is pretty loud now and steering a bit weird at low speeds

I changed the fluid to correct type and now whine is really loud


Could be air in the system, run it for a while and see if it quiets down, if not you can put in some power punch to help, it will blend in and help clean up some of the valving in the steering box, pump and the cooling fan. Hopefully the unspecified fluid wasn't covering up a power steering problem.

I drove it for awhile and it still made noise . So I'm gonna check it later to see.... Is it possible my Jeep 4.7 gets 21 mpg doing a pretty consistent 45mph that's what it says average mpg is ?

It's says that on the overhead display btw


That sounds too good, my old Cherokee 4.7 fuel mileage was 14.2 with an average speed of 42mph. Could be the PCM is messing with the readings, of course you could conduct your own fuel mileage tests.

Lol . Was thinking the same because fuel gauge seems to move alot more than 21mpg

Anyways, earlier pump was still pretty loud when I drove it. I drive it about 11 miles after changing the fluid, hopefully the air works it's self out it as it didn't make much noise before. The old fluid was wrong kind and was foamy .

How can I bleed the power steering its still whining changing the fluid didn't help , the old fluid was foamy which leads me to believe there's air in the system


It maybe a bad pump, the front seal maybe allowing air to be introduced into the pump body itself, does the new fluid also have air in it?

Seems like it, I was whining loud after I changed it. The whine has quieted some but its still noticable .

I'm convinced there's air in the system because old fluid was really foamy and after I changed it the whine is the same. Just like before


I have had some success with Power Punch if the seal is leaking even slightly, but follow the directions, too much and it will really fouls things up. Give it a try and if your still getting air in the system then after 20 or 30 miles then to get rid of the noise your going to have to replace the pump.

Does it help get rid of air in the system ?


If the air is getting in the system through a weeping seal it will, but if the pump is just worn it won't.

So is the pump self bleeding or does it need bleed maunal

Also I do not believe it was whining when I bought it. It didn't start till i replaced radiator and I have to take fan and stuff out so I had took unhook hoses and some fluid ran out. So when I was done power steering fluid was a little low due to pulling the line off . I noticed it when I started it it had a whine and I topped it off but has had a whine ever since


It is self bleeding, but if you have an air seepage it will never bleed it all out, recheck the fan fittings, possibles of a nicked seal is high as you had to take it apart, once the correct fluid was installed and it has run for about 20 minutes the air should be all out, especially if you cycle the steering wheel lock to lock to a few minutes, if it doesn't clear the air then you have an air leak, and they are hard too find, but start with the work previously done.

Only power steering line I had off is the line that runs from pump to the fan . I'll check it out.

I'm confident that it's not the fittings though because I had some help taking the lines off from a person who's very knowledable of cars

But if there's a gasket letting air in wouldn't it let fluid out to ?


A gasket yes, but a seal is a different story, I had a power hydraulic pump on an old tractor that was fine when you first started out but as it ran the thing would start to sound like it was out of fluid and the 3 point would jump as it was raised or lowered, check,the fluid and it was all foamy, shut it off and let it sit for a while and it would be fine again. Finally one day I got mad at it and yarded the pump off and what I found when I took it apart was there was a small groove in shaft on the pump and there was some minor back and forth motion of the pulley, now maybe a 1/16 of an inch didn't think too much about that but when measuring everything I found that when the shaft moved it would run that little grove just outside the seals lip then back again so everytime the pumps pressure rotor came up to pressure the shaft would move and everytime it moved it would drag in just a little air, never leaked any fluid, repalced the pump and no more problems with the air in the pump or the 3 point deck. So I don't know if that is the same as your problem but you might see if you move the power steering pulley in and out, if you can then that MIGHT be your problem.

See when I check my fluid in reservoir it's not foamy , no bubbles or anything. The whine now is not to loud u can hear it but not much it increases a little as you turn the wheel and give it gas. I think pump may just be a little worn


It could be that the wrong fluid has left some residue and the new fluid is trying to clean it up, I'd just drive it and not worry too much about it until it starts to have trouble steering.

Yeah it steering good . No issues other than when just rolling like trying to parrell park steering gets stiff for a sec.. would you happen to know if power steering fluid ms5931 comes in a red color ?


MS5931 and MS9933 are Amber/Yellow in color. All three fluids will darken in color with usage and fluid color is no longer an indication of fluid condition. Right out of the Chrysler TSB. So it is not Red.

I wanted to make sure . Bc the power steering fluid I drained was red . So it definalty was the wrong fluid

So with it having the wrong fluid in it. And now changed to correct I driven it about 39 miles and the whine has quieted some . Is it possible that the whine will quiet even more over time since now it has correct fluid

Also I noticed I didn't drain all old fluid out I noticed resoviour still has red fluid in it . Should I get the rest out ?


You really should flush it.

I think the little bit of old fluid is pretty diluted by new fluid I drained it then added about one whole 32oz bottle and the 2nd 32oz bottle has about 8oz left in it. That put it to proper level


If there is enough to change the color to red it is still too much.

I think last time I looked, there was a little red mixed in with it in the resoviour.

Could the whine still be from the leftover fluid ?

This is the old fluid

So is this definalty the wrong fluid ?


Yes to both questions, it may have left a residue that the new fluid is having a problem getting cleaned out. That looks like ATF.

I was thinking the same .although it Smells like power steering fluid

How much does this thing hold iv used two 32oz bottles and there's still red fluid


Factory refill is really close to 32 oz. give or take a couple of oz.

Do u know specs for antifreeze for my Jeep? is Chrysler MS 7170 ok for my car.


Your jeep requires an HOAT compliant coolant MS7170 is compliant, but you need to know if you have compliant coolant in there now, you can't mix it with non compliant. So if there is any doubt flush the system with water then drain and refill make sure you have at least a 50/50 mix of coolant with distilled water. Colder areas will need a heaver mix of antifreeze.

Coolant I have now says compatiable with Chrysler 2000+ . Fluid I looking to get to top it off says meets Chrysler specs and is compatiable with all green antifreeze

Seems like they both meet specs for my Jeep so I think it's safe to get the fluid to top mine off

I'll just get the same kind that's already in it to be safe


that should do it for now.

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