17th Jan 2009, 22:01

If you cannot get the codes yourself, you can go to Autozone and they will read them for free.

Also you can disconnect the battery for 2 minutes and the computer will reset itself. This will turn off check engine light. If anything major is wrong it will come right back on. If it is just a ghost code, like the misfire code, it will not come back on until it misfires again.

12th Feb 2009, 11:59


This is just an FYI, I see a lot of questions but few resolutions to codes.


Working on my friends 1997 Jeep GC, 4.0L., 150K.


Multiple misfires. Check Engine Light. Throws a 43 (coil current error) from the key-on-off-on diag method.

Scanner shows P300, P304, P305, P306. This is multiple random misfires, cylinders 4,5,6.

O2 voltages bounce, but seem good range.

Timing bounces (due to misfire) at idle.

Idle rough, but not terrible.

Vacuum reading about 17 +/- 1 inch when engine misfires.

MPG not bad, getting about 20mpg.

Checked electrical tests, all good. Checked fuel pressure, okay. New tune up about 10K ago, including plugs, wires, coil, cap, and rotor.

Crank position sensor is new, as I broke the old one when we rebuilt the trans.

O2 sensors new.

We recently replaced the exhaust manifold as the old one was cracked, so I suspected possible vacuum leak at the intake (cyl 4,5,6 are adjacent). While idling vehicle cold, I doused the intake gasket area with starting fluid. Slight rise in idle momentarily, but not bad. (yes, that is not a good thing).

Once warmed up, I did it again. Put a direct hit on the injector where it inserts in the manifold, and WOW! The misfire was very noticeable. Did it again on all injectors, one at a time, and found that the only one that did not matter was cyl 2. #6 just about stalled the vehicle.

The O2 sensors read about.8v (very rich) when I sprayed the injector holes.

Final diagnosis: bad injector seals.


Code scanner: $200 (CP9185 from advanced auto)

Injector seals: $9 (advanced auto)

Time about an hour to diagnose and change out.

(Actually this the 10th time I used the scanner in the past 2 weeks).

Peace of mind not getting taken by the dealer:

PRICELESS!!! :D :D :D :D :D.

So, for anyone getting those codes, do your research, and check those seals.

Things to watch out for:

The new seals are tight. Use some dish soap to lubricate before putting injectors in. I use electrical connection grease (very light coating).

Use caution with the starting fluid (fire risk). Have an extinguisher in your garage. You do have one, right??? ;)

Hope this helps someone out there. :D.


27th Mar 2009, 12:54

I wish I'd found this thread last night! Right now my 2001 Jeep Cherokee 4.0 is in the shop, being "diagnosed" b/c my malfunction indicator light (aka check engine) came on yesterday.

This is my second Jeep - the first was a 1990 Jeep Cherokee that I drove until it couldn't drive anymore - had almost 300,000 miles on it and the check engine light never once came on.

I've had this 2001 Jeep for about a year, keep very regular maintenance and upkeep on it, and know the previous owner did, too. It has just over 60,000 miles on it, and this is the first indicator of problems I've had so far.

My brother also owns a 2001 Jeep Cherokee, and both of our right front speakers and right front window controls work on and off.

I really wish I'd read to bring it to Auto=zone or check the error codes myself (did not know about that!). So, will just wait to hear my estimate and then make a decision from there.

Thanks for all of the advice! Very, very helpful, especially if this is going to be a recurring problem! I now know a couple things to do first, instead of bringing it right into the shop.

2nd Apr 2009, 23:40

Update on above post.

Got my car back from that shop, but they couldn't find any problems, after having my car for 2 days. They cleared the 2 codes and turned the light off.

Two days later, the light was on again. THIS time, I tried the self-checking tips for the codes, but the trip reset button one never gave any, just my mileage, and we couldn't get the run-off-run-off-run to work.

Brought it to the dealer next, figuring they would know Jeeps best. They found 1 code - fuel leak. I had been smelling gas and mentioned this. Turns out, my gas cap had been rusting and corroding, so wasn't creating a good seal. They replaced it, ran the test again - no codes and the light went off.


12th May 2009, 10:07

My 98 Cherokee Sport 4.0l has been plagued with the 'Check Engine' light for a while now. Here are some things of interest I have found:

1. The odometer thing (holding the reset button in and switching key to 'run') for the OBDII code does *not* work. It will cycle through 111111, 222222, etc., but at the end it does not show the serial number or codes.

2. The run/off/run/off, etc. thing does *not work*.

3. I went to Sears and bought their cheapest OBDII scanner, the Actron PocketScan. Normally $79.99, but on sale right now for $49.99. It works like a charm. It showed codes 300, 303, 305 and 306. 300 means random misfirings, 303, 305 and 306 mean misfiring on cylinders 3, 5 and 6 respectively.

4. Used the 'Erase' function on the new scanner to clear the Check Engine light and error codes. After driving a bit the light came back on. The scanner showed 306. I cleared the errors and ran it again several more times and each time got the Check Engine light back with the same 306 error code.

5. Plugs are new (Bosch) and plug wires are new. I blew a head gasket not long ago and replaced it. Head was in good shape, but I didn't bother decarbonizing or even re-seating the valves.

6. There's some good things to try in here (as well as some pretty questionable theories), so I'll give them a shot and put the results here.

22nd Jun 2009, 14:50

Check engine light problem was resolved by my Jeep Mechanic. The fix is, 1 asbestos wraps around the 1,2,3 injectors to stop them from over heating. 2 the computer needs to be updated. Once that was done I had no issues. I hope this helps. No service station could figure this out.

18th Sep 2009, 23:07

Where and how do you get the asbestos wrap and the computer updated on an 01 jeep cherokee?

21st Mar 2010, 13:18

I comment earlier too: engine light and airbag light on. Not all the time, but pretty regular.

I knock sometimes on the plastic cover for the instruments then it comes off, but light up again after a while. Will try to follow ALL the things people recommended.

At one point a mechanic said perhaps the computer unit must be replaced!!!.

Question; my car got about 130.000 miles on it, drives great. How long those engines last??, Because when it's gone I'd like to buy a rebuild or brand new one. Any comments??? How costly??