The Dreaded CEL

Alright, my I went mudding in my bro's XJ for thefirst time. Nothing to hardcore but afterwe were done I noticed the cel on and the voltmeter was just above the red zone. So I pop the hood and everything under it is covered in a thick coat of goopy mud. So I take it to a local quarter wash and hose the engine down. On the way to a friends house I notice the headlights are dimmer than usual along with the cluster lights. So pull the codes and get a 11, 41, 51, 55. I disconnect the battery and then run the codes again after running engine for a few min. The 11 went away and was replaced with 12. So now the codes areas follows:
12-Direct Battery Input to Powertrain Control Module (PCM) disconnected in last 50 key-ON cycles
41-Alternator field is not switching properly in response to PCM regulator signal
51-HEGO Sensor indicates constant "Lean AFR" condition
55-Indicated display of DTC's is finished

So the 12 makes sence cause I did just disco the batt. What should I check for the 41 and 51?

Thanks, and by the way the XJ is a 92 4.0 AX4

My suggestion? Wait a few days for things to dry up. Then see if you still have problems.

You could try WD40'ing the alternator or hairdrying it, since both displace water.

Maybe the lean condition is caused by that as well, unless you flooded a sensor too. What year XJ?

Blaine B. said:

You could try WD40'ing the alternator or hairdrying it, since both displace water.

Maybe the lean condition is caused by that as well, unless you flooded a sensor too. What year XJ?

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Gawd. No. Don't!

If you want to flush out your alternator, use plain, clean water (preferably distilled or R/O filtered) and nothing else!

It's true that WD-40 displaces water - but it also leaves a film on things, and I'm tired of cleaning it off because people keep mistaking it for contact cleaner.

It is:
Water Displacing
Something that can "get under" glue on labels.

It is not:
A contact cleaner
A lubricant
A "miracle in a can"

Sorry, but if I hear one more person tell another person to use WD-40 on something electrical, I'm probably going to reach for my cricket bat next.

Please, for the love of God, stop doing this! I'm tired of diagnosing WD-40 related electrical malfunctions, and have been for years...

To flush out your alternator, either use plain, clean water (as previously mentioned) or a dedicated electrical contact cleaner - which is designed to not leave a film, not corrode anything (electrical contacts are notoriously susceptible to corrosion) and will get your contacts clean very easily.

If the cleaner spray doesn't work on an exposed contact, I find that Pink Pearl rubber erasers (yes, the ones you used in grammar school) work wonders for abrasive cleaning of copper contacts. Keep some in your electrical kit.

excellent advice 5-90 , only thing you forgot to mention is just how flammable wd40 is .
spraying a bunch of it into anything electrical while it is still live , and / or starting it just after would be bad . :flame:

only use i have for wd40 , is with a lighter as an impromptu bug erradicator , works great on spiders.:thumbup:
( almost as good as brakeclean )

sw_mi_xj said:

only use i have for wd40 , is with a lighter as an impromptu bug erradicator , works great on spiders.:thumbup:
( almost as good as brakeclean )

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Also works good for removing Tar off the side of your Jeep when you drive down that road that's being repaved :banghead:

I'll x2 the eraser theory. This works very very well on almost anything that you're having problems with getting juice to, even simple electronics. I've had several small electronics stop working, or work on half power even with new batteries. Took a purple eraser to them, cleaned all the contacts, and they worked just like new again!

Well I just drove it up on blocks and hosed the entire engine bay and undercarrage. Now its drying, so I guess Ill wait a day till I pull the alternater. I just can't wait too long cause I'm leaving for VA on Monday, I'll be gone a week and if my bro needs to use the car I don't want the alt. to decide to grenade on him while I'm gone.

jesusjeep19 said:

Alright, my I went mudding in my bro's XJ for thefirst time. Nothing to hardcore but afterwe were done I noticed the cel on and the voltmeter was just above the red zone. So I pop the hood and everything under it is covered in a thick coat of goopy mud. So I take it to a local quarter wash and hose the engine down. On the way to a friends house I notice the headlights are dimmer than usual along with the cluster lights. So pull the codes and get a 11, 41, 51, 55. I disconnect the battery and then run the codes again after running engine for a few min. The 11 went away and was replaced with 12. So now the codes areas follows:
12-Direct Battery Input to Powertrain Control Module (PCM) disconnected in last 50 key-ON cycles
41-Alternator field is not switching properly in response to PCM regulator signal
51-HEGO Sensor indicates constant "Lean AFR" condition
55-Indicated display of DTC's is finished

So the 12 makes sence cause I did just disco the batt. What should I check for the 41 and 51?

Thanks, and by the way the XJ is a 92 4.0 AX4

Click to expand...

I would pull the alternator, dissasemble and clean it properly. Then reassemble it and then take it to someplace like autozone to get it tested. Sounds like a voltage regultor (internal) or diode problem. May just be the dirt, or may be burned out due to the dirt.

Well I pulled it out, flushed it very thoughly with water. Dryed it with an air compressor, let it sit in the sun for a while, the reinstalled it. Drove it a couple miles and all the same symptoms(voltmeter in the red, cel on) When I got home I pulled the codes again and this time the 41 got replaced with a 21-HEGO Sensor Input voltage maintained above normal operating range. For the voltage problem, I'm just going to put my spare alt. in and have the current one tested. Could I pull and clean the downstream HEGO to fix the code 21? Or should it just be replaced? Thanks for all the help.

Ecomike said:

I would pull the alternator, dissasemble and clean it properly. Then reassemble it and then take it to someplace like autozone to get it tested. Sounds like a voltage regultor (internal) or diode problem. May just be the dirt, or may be burned out due to the dirt.

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If he's got a CEL lit, it's HO, and that means an externally-regulated ND alterantor. The voltage regulator is in the PCM.

I suggested using R/O or distilled water (as a final rinse, if nothing else) because tap water has dissolved metals and solids in it - and they can cause deposits, which cause trouble. This is why you don't use tap water in a radiator or in a battery.

You probably need an alternator. I fried more than a couple in my old '91 XJ while wheeling myself, and they always triggered a CEL with that code IIRC. The geniuses at AMC decided to mount it nice and low, so if you drive through any mud or water you'll soak it. You can try cleaning it out and hope for the best, but I'd just run to AutoZone and get a new one with a lifetime warranty. Install that puppy, and wheel all you want. Believe me, the next time you fry one in the mud they'll warranty it It is externally regulated, but I never had a problem with the regulator in all the alternators I drowned. Then again, my gauge always dropped gradually as the battery drained after the alternator died...I don't remember it ever going UP past normal. It is possible you have a regulator issue...might want to get the system tested.

As for the Code 51, lean condition...I don't know offhand if a Chryco OBDI scan tool will allow you to read fuel trims or A/F ratio. I'd start by checking for vacuum leaks and exhaust leaks before that sensor before you just go and buy a new O2 sensor you may not need. It's possible that you knocked a vacuum line off or broke something that resulted in a vacuum leak while plowing through the mud.

Well I'm sorry, I've heard of uses where WD40 on the alternator did wonders. Yes it is flammable, that's why they let it sit overnight. I never heard any fires after letting it sit.

Blaine B. said:

Well I'm sorry, I've heard of uses where WD40 on the alternator did wonders. Yes it is flammable, that's why they let it sit overnight. I never heard any fires after letting it sit.

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Understood. But if I had a dollar (Hell, a nickel!) for everytime I've found a WD-40-related electrical problem, I wouldn't need to work anymore.

Using WD-40 to "clean" anything electrical is like using a wrench to drive a nail - you can probably do it, but there are better ways to solve the problem!

I'd have to be very hard up to use WD on anything at all electrical. Discounting the flammability issue, there's just the degradation of the contact between the terminals that you get from the film that WD-40 leaves behind. Electrical contacts don't like being coated with anything - and corrosion inhibitors are designed and formulated to completely "squeege" out from between the contacts upon reassembly. WD, on the other hand, is designed to stick to surfaces, and it typically requires a mild solvent to remove (trichloroethane, acetone, or xylene all work wonders. Too bad you can't find them easily in CA anymore. Damn CalEPA... More on that elsewhere.)

In all honesty, you're really better off using clean water to flush out electrical contacts than you are using WD-40.

Endeth the sermon (that I've been giving about twice a month for, oh, 20 years or so...)

I didn't get time to put in the spare alt cause I had to work. But after work as I was leaving I noticed my gauge lights were almost not even lit, then the tach dropped to zero. So I was like CRAP! Luckily my brother lives about half a mile from my job, so i turned off my headlights to save power and made it to my bro's. So I now know for sure the alt. is dead. Tomaro I'll put in the spareand hope its good. And I'll start checking the vaccum lines for the code 51. Thanks

Put the spare in today and everything is back to normal. On the drive home from my brother's the cel was still on though, It was pulling a code 21. But after I got home I started the jeep to move it and the cel was gone. So I let it run for awhile and it never came on. So I guess all is fixed.

Any jeep line (ChryCo/Renix) doesn't like wonky electronics, so the gas gauge may be out, weird lights and the CEL may be thrown. Normally a few miles and some high-idling sorts it out.

5-90, if contact cleaner wasn't available......would brake cleaner suffice?

Two things I have plenty of are both WD40 and brake cleaner

I was thinking earlier today, could it be possible to shield the alt? Like a box around it or something of the sort. I'm sure it has to be well ventilated but just something to give piece of mind to the XJ driver?

x2 bout the brake cleaner. I was gonna use that the other day but wasn't sure so I decided against it.

Blaine B. said:

5-90, if contact cleaner wasn't available......would brake cleaner suffice?

Two things I have plenty of are both WD40 and brake cleaner

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Brake cleaner should work - although the "environmentally friendly, non-clorinated" stuff just plain sucks. It works, but it takes four times as much of that as it does trichloroethane (the previous brake cleaner, that actually works well...)

A good shield for the alt would probably be a skid plate.....since there's plenty of room for air to circulate behind it, while it would also prevent the alternator from getting splashed on.

Do both of the brake cleaners cause cancer? I heard it did, never knew about two different types however.