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View Full Version : 196k miles and my first "CheckEngine" light ...



ChiefRocka
03-02-2014, 05:38 PM
So .... I was surprised to see that light come on.

It runs soooo good.

Off and on, nothing has changed in driveability ...

So now, how do we check for codes on this 94 ??

XJ Wheeler
03-02-2014, 07:04 PM
This is the write-up i went by when i checked mine.

http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/

Sent via messenger pigeon - i talk, he types.

97justin99
03-03-2014, 01:25 AM
Out here Auto Zone will check your OBD for free and give you the code but not clear it. If you can get the code and fix the problem then disconnecting the battery for a while or over night should reset the check engine light ( and your radio setting :( ). O'Reily will let you borrow the reader get your codes and you can clear them on your own, they just want to borrow your drivers license while you borrow the tool.
This is for OBD 2 on a 99xj I assume it would be the same for OBD 1
196k miles before it nags at you nice. Hope it's just a nag.

JeepFreak
03-03-2014, 02:29 AM
You have to "Key Dance" the key lock cylinder. Super easy. Sequence the turning of the key like this: ON-OFF-ON-OFF-ON then wait for a few seconds as the light flashes (the check engine light) and when I say 'ON' I mean to accessory NOT starting it. The check engine light will flash in sequence of the numbers corresponding to your OBD 1 system (I have a 1994 and it has the same system, OBD 1) Anything after 1996 has OBD II. Let's say you have a code 12 (Battery disconnected from PCM within 50-100 starts). It will flash (the CEL) like this: One flash -long pause- one flash -shorter pause- one flash. When it is done reading off the TWO digit codes it will flash a 55 like this: flash -pause- flash -pause- flash -pause- flash -pause- flash -longer pause- flash and pause 5 more times. When it reads a code 55 that means there are no further codes to report. I have the Chilton guide with EVERY code for our 94's so just key dance it and tell me the code and I can look it up. No need to drive somewhere to have it done when you can do it in 30 seconds. And clearing the code is no biggie either. It will reset and clear it (but it will be 'stored') once the engine's PCM has determined a normal start sequence and run sequence for 25 consecutive trips in a row. You can disconnect the battery but as an auto student we are taught not to do that as it could cause a surge in the computer (it has capacitors that can deliver a surge if disconnected). So unless you ABSOLUTELY have to do NOT DC the battery.

ChiefRocka
03-04-2014, 10:38 AM
It worked guys thanks !!!

I got a CODE 41 ... "alternator field switch"

Best approach ... New alternator ??

OG unit still in Jeep

4.3LXJ
03-04-2014, 10:40 AM
That sounds about right

JeepFreak
03-04-2014, 12:22 PM
It worked guys thanks !!!

I got a CODE 41 ... "alternator field switch"

Best approach ... New alternator ??

OG unit still in Jeep

LOL I JUST had this same issue and I had to replace practically everything in my charging system. Code 41 means "Voltage Regulator Control Signal is not responding to the Alternator field generator" which pretty much means one of a few things.

1) Your alternator is bad (take a DVOM and place the positive on the wire leading back to the battery and the ground on the casing of the alternator to test how much voltage is being created when the car is running).

2) If the alternator shows up fine(at least 14.2v) both at idle in park and at high idle with headlights and HVAC on (at least 2500RPM) you need to clean EVERY ground you can find. The battery ground, PCM ground, engine ground, A/C;alternator;starter grounds, everything.

3) If that STILL doesn't work, you will need a new PCM. The problem with ALL jeeps is that the Voltage Regulator CANNOT be serviced or replaced because the regulator is transistorized meaning it is either internally mounted in the alternator or in the PCM. Most likely it is in the PCM and if this is the case it CANNOT be repaired it must be REPLACED.

You can either buy one new from Rockauto.com for 161 bucks and change (remember I have the same exact year as you) or go to PnP and get one for around 25 bucks. Either way, if it's your PCM, you're in a world of hurt.

The way I fixed it was to do EVERYTHING I stated above and I didn't have to replace my PCM. In fact the grounds were extremely corroded so I cleaned those off and every metal connector down to silver colored steel with a wire brush. I replaced the alternator (since it was the 22 year old factory installed one) and the starter (even though I didn't have to in this case but it was taking longer than normal to start which means the starter could be going bad) and my XJ works great for me. Code 41 went away the first time I started it (which is not usually the case but who's complaining?). Let me know if you need help tracking those grounds down. After 196k miles, they aren't going to look good especially since I'm almost at 267k.

ChiefRocka
03-04-2014, 05:25 PM
Interesting, lets just hope it is not the ECM.


I forgot to mention I have been driving the Jeep for about a week or so without a loss of battery voltage.

Also, the check engine light is intermittent .... every 4th or so start up..... sometimes a day or so.

Ill check the voltage when I get back to my shop, but I bet I will find 14 volts.

I will carry a voltmeter with me and recheck when light it on.

Meanwhile, all grounds will be polished !!

ChiefRocka
03-04-2014, 06:13 PM
Ok .....

13.75 Volts constant

Idle and high rpm, no change

Lights and A/C on, idle and high .... and no change

A constant 13.72/13.76 voltage.

Either the alt is bad, or the ECM is not controlling it.....

JeepFreak
03-04-2014, 07:52 PM
Sounds like you have a bad alternator. My voltage never changed either (and it should with a load change whether electronic loads like a headlight or A/C or mechanical such as RPM) and was always at a constant 13.74v. The absolute minimum you want the voltage to be at is 14.2v. Very highest, it should not go above 14.6v. I replaced my alternator, cleaned the grounds, and everything was fixed. My CEL was intermittent too. Problem was I ignored it for too long and 3 days later my Jeep sounded like it was going to die any moment. Try polishing the grounds and be sure to GREASE the bolts you remove (from anywhere even if it isn't a ground bolt) with dielectric grease for alternator bolts. Helps a bunch and prevents resistance from forming. Replace the alternator as well and don't listen to autozone. They told me that my alternator was FINE without any loads whatsoever but we all know that there's a bunch of loads once a car starts so that is inaccurate. They told me "oh it must be your PCM" and I was like "just give me the new alternator you ****s". (EDIT: I said t w a t not the f bomb lol)

Floridajeepcherokee
08-31-2014, 03:19 PM
My digital multimeter dropped to under 10 volts with engine running so is it a bad alternator or bad pcm? I read that Jeep's voltage regulator is in the pcm. If the volts are under 13 with jeep running I would think my alternator is bad. I had charged battery overnight then the multimeter showed it dropped below 10 volts dc with the jeep running.