Replacment ECU

My brother in law is looking for a replacement ECU. What would be his best resource to aquire one. Thanks

First of all, be darn sure the issue has been diagnosed properly because a lot of computers are replaced only to find out that wasn't the problem. Rule out all other possibilities first (diagnosis of exclusion).

There are some sources on the internet (search) but another great resource is a salvage yard. The price you will pay is significantly less and as the computer is hearty, salvage yard units will often give you a long service life.

What year is his? Is he in CA too?

I have to agree with birchlakeXJ, ECU's very seldom go bad. I've only seen an ECU replaced once in the time I've been a tech, and that one needed to be replaced because the car got hit by lightning.
What ever the reason may be try http://www.car-part.com

I bought a '98XJ that wound up having a bad ECU. Symptoms were no activity from the volt meter and fuel gauge with the key on, code P1694 was active (but the check engine light was NOT on), and the truck had no spark. I'm not sure if the fuel pump still worked since that also wound up being bad.

I did read that ECU's very rarely go bad, so I was confident in buying a used one on e-bay. I just matched the numbers from the one I pulled and got one for about $75 shipped. Popped it in and the truck fired right up (after I replaced the bad fuel pump, of course).

TerraWombat said:

I bought a '98XJ that wound up having a bad ECU. Symptoms were no activity from the volt meter and fuel gauge with the key on, code P1694 was active (but the check engine light was NOT on), and the truck had no spark. I'm not sure if the fuel pump still worked since that also wound up being bad.

I did read that ECU's very rarely go bad, so I was confident in buying a used one on e-bay. I just matched the numbers from the one I pulled and got one for about $75 shipped. Popped it in and the truck fired right up (after I replaced the bad fuel pump, of course).

Click to expand...

Ive also heard they rarely go bad. However, I'm still trying to diagnose my problem and after reading your post I'm thinking this may be the issue. I bought my jeep not running off a buddy. Had no fuel pressure so replaced the pump...new pump didnt kick on. My voltage meter and fuel gauge doesnt read, and I have no spark. I have tried connecting an OBD II but there was an error so it wouldnt connect. I think I'm going to look into finding an ecu now... Thanks for that post! :thumbup:

BTW...the Jeep I bought is a 98xj sport 4.0

mattynicks3 said:

Ive also heard they rarely go bad. However, I'm still trying to diagnose my problem and after reading your post I'm thinking this may be the issue. I bought my jeep not running off a buddy. Had no fuel pressure so replaced the pump...new pump didnt kick on. My voltage meter and fuel gauge doesnt read, and I have no spark. I have tried connecting an OBD II but there was an error so it wouldnt connect. I think I'm going to look into finding an ecu now... Thanks for that post! :thumbup:

Click to expand...

STOP! Test, test, test, and did I mention TEST?

Check the CKP/CPS crank sensor. When they short to ground the scanner's won't be able to connect with the PCM--common issue.

mattynicks3 said:

Ive also heard they rarely go bad. However, I'm still trying to diagnose my problem and after reading your post I'm thinking this may be the issue. I bought my jeep not running off a buddy. Had no fuel pressure so replaced the pump...new pump didnt kick on. My voltage meter and fuel gauge doesnt read, and I have no spark. I have tried connecting an OBD II but there was an error so it wouldnt connect. I think I'm going to look into finding an ecu now... Thanks for that post! :thumbup:

Click to expand...

could be the pcm/ecu, but i would make sure you have a good connection at the back of the gauge cluster. if there is bad connection with the gauge cluster, i dont think the pcm/ecu will work proporly.

its just a thought before you buy a part that may not be needed.

mattynicks3 said:

My voltage meter and fuel gauge doesnt read, and I have no spark. I have tried connecting an OBD II but there was an error so it wouldnt connect :thumbup:

Click to expand...

Joe is right (and is angling for another cookie!) Here is a thread that you should read regarding the crank sensor.

http://naxja.org/forum/showthread.php?t=1025391

Note the part in there about no spark and that the voltage and fuel gauge may not work. Sound familiar?

Test the crank sensor and something else you should try is removing the connector for it, then check your volt and fuel gauge; if they start working with the crank sensor disconnected, you have found the source of your problem.

mattynicks3 said:

Ive also heard they rarely go bad. However, I'm still trying to diagnose my problem and after reading your post I'm thinking this may be the issue. I bought my jeep not running off a buddy. Had no fuel pressure so replaced the pump...new pump didnt kick on. My voltage meter and fuel gauge doesnt read, and I have no spark. I have tried connecting an OBD II but there was an error so it wouldnt connect. I think I'm going to look into finding an ecu now... Thanks for that post! :thumbup:

Click to expand...

When you put the key into the 'on' position, do you get a reading on the volt meter or fuel gauge? The volt meter should jump up to around 12 volts (battery voltage) and the fuel gauge should show you how much is left in the tank. If you disconnect the crank position sensor located at the top rear of the intake manifold (three pin connector) and your gauges suddenly come back to life (assuming they were dead to begin with) then your culprit is a bad CPS. You can also measure the resistance of the CPS and there are guidelines on how to do that floating around here somewhere. You can also google 'cherokee crank position sensor testing' or something similar to get the instructions on how to do it. The reading is supposed to be 'open' but even on two BRAND new sensors, I wasn't able to get an open reading, but I did get a very, very high resistance between the pins which is almost like being an open connection

The cps is brand new. i tried doing the whole unlpugging and plugging back in with the new and old one and it didnt make a difference. One of my buddies thought like 2 weeks ago it was the ecu, the other is thinking its a wire somewhere. We've checked wires like crazy and havent really found anything odd looking with the exception of one wire that I believe is light blue, that hangs down by the drivers side kick plate. I brainstormed a little bit and noticed that when the drivers door (only that door) is open, I dont get a buzz noise or the interior light does not come on like it should. So my guess is that what the wire was for...if I'm wrong please correct me! Ive also checked grounds in the engine bay and everything seems fine. the ones that seemed like they could be questionable I took off and cleaned up then put them back.

Also as far as the fuel issue goes, the pump only kicks on when we jump the fuel pump relay. We've swapped relays to make sure the fuel pump relay wasnt toast but nothing changed. Could the ecu not be doing its job by not telling the fuel pump relay to kick on? We're running out of ideas and could use some input, thanks.

mattynicks3 said:

The cps is brand new. i tried doing the whole unlpugging and plugging back in with the new and old one and it didnt make a difference. One of my buddies thought like 2 weeks ago it was the ecu, the other is thinking its a wire somewhere. We've checked wires like crazy and havent really found anything odd looking with the exception of one wire that I believe is light blue, that hangs down by the drivers side kick plate. I brainstormed a little bit and noticed that when the drivers door (only that door) is open, I dont get a buzz noise or the interior light does not come on like it should. So my guess is that what the wire was for...if I'm wrong please correct me! Ive also checked grounds in the engine bay and everything seems fine. the ones that seemed like they could be questionable I took off and cleaned up then put them back.

Click to expand...

You need to pin out the harness with a multimeter to check for an open or shorted wire.

Any chance you have a security system with an ignition interrupt?

The only difference I can see between your scenario and mine is that I was able to get a reading from the ECU when I plugged my code scanner in, but all of the other symptoms seem to be identical. I was also not able to get power back to the fuel pump unless I jumped the relay, but my fuel pump was also TOAST. When I put the new (used) ECU in, I then was able to get a reading at the fuel pump wiring harness (and the fuel pump relay also clicked), but the pump still didn't run but that was because it had been sitting in stale gas for the last six years and was not a happy camper. After the fuel pump was replaced, the truck started right up.

So, if you're not afraid to spend a little bit of cash check out some ECU's on e-bay. My particular ECU part number was P56041 534AE (should be a '98XJ w/federal emissions). I wound up buying an ECU out of a '98XJ with the part number P56041 534AD. The letter codes correspond to the revision of the firmware, so AA would be Version 1, AB is newer (maybe Version 1.1 or 2.0, dunno). As long as you get the numbers right, the letters don't matter. I guess if you want the latest ECU flash, go for the AE or AF (I'm not sure they went much further than that).

it's funny how everyone says ecu's dont go bad, but ive had one go out, pretending to be a cps issues. if something tells you its the ecu, try it, the naysayers in this thread dont know everything...

swapping it out takes 5 minutes, and will give you an easy answer. (thank you cal)

ecu's fetch a premium at the junkyard (they think 'computers? LETS GOUGE!')

i STILL wouldnt buy a new one, as the retailer i delt with was TERRIBLE.

joe_peters said:

You need to pin out the harness with a

Any chance you have a security system with an ignition interrupt?

Click to expand...

No security system joe.

But everything else seems to be working like it should...There's a new fuel pump, CPS, ignition coil, fresh fuel, and a new battery, so I think if I can find a relatively cheap ecu at a junkyard I'm going to give that a shot. Who knows it could be the miracle fix, and if not...then I'll have a spare.

Well, be sure and post a followup and let us know.

Will do. Probably won't be right away but when it happens I'll let you guys know.

I think I already told you to check Sam's for parts in another thread - I seem to recall them charging 50 for ECUs. Pretty sure there is a 99 in the yard right now, there might be a 98 or two as well, there were 3-5 97-up models there last time I went. Like everyone said just match the part number, the letters at the end are the revision code, that can mean updated hardware or firmware but more likely means firmware so if you notice fluky stuff you can bring it back to the dealer for an update on the firmware, depending on if there was a recall for it they might or might not charge you for flashing it.