Topic: strange check engine light today.

[littleredbeater]

I got in my 91 yj to head to the gas station and the check engine light was on at start up. After fill up it was gone. Next stop Sears, when I came out and started it I got the light again. While sitting at a light I shut it off to unlock my glove box to get my radio (I hate that!) and when I restarted it was gone. Anyone ever had this happen? I didn't notice it running any different. :?

[Jeffy]

Hard to say.  I'd see if the computer stored any error codes.

Follow these steps and the codes should be the same for the YJ.

http://www.kcjeepclub.org/info/tech/tj_error_codes.php

[littleredbeater]

I'm thinking she might be pissed that I'm spending so much on gas and not buying any jeep parts lately. haha If I find anythinginteresting I'll post it.

[BerkshireJeeper]

I've had this problem before. Try taking the gas cap off and then putting it on and making sure it's on tight (3 clicks). I forget what code this is but it has to do with either using bad gas (mine came from Mobil twice) or just not having a sealed gas cap. Try that...btw my Jeep is mad at me for not buying parts also.

[Jeffy]

I don't think that should matter or bring up a light on a ODBI.  I think that's a ODBII 'Feature'.

[Skinny]

91 is OBDI compliant all the way up to 95.  The number of codes the ECM stores is very limited.  An OBDII on a 97 and up, however has 200+ reasons to make that light come on.  The gas cap seal/no seal doesn't affect OBDI vehicles.   There is another code flow chart for the YJ's it has to do with the number of times the engine light flashes after cycling the key in a certain pattern.  Don't know off the top of my head where it's at though.

[Jeffy]

That chart for the 97' TJ works for the YJ...

[Skinny]

Jeffy is right, the TJ will flash the engine light the same as the YJ will, the flow chart is just different in some ways. The 97 up will get more specific on the problem with a scan tool instead of just the number of flashes.
For the YJ though it's pretty straight forward, if you need help after you get the code with pulling some diag. info post it and I can try to dig it up from ALLDATA for ya.

[littleredbeater]

funny thing is the light clears on restart, usually it takes two drive cycles to clear a pending or stored code doesn't it? That's what was  weird to me. start it.... there. restart it..... gone. start it...... there. restart it......gone. Hasn't happened since though. I was kinda looking for a reason to work on it some more. haha I still need to port match my intake, TB and spacer; and I figured I'd put on the header while I'm in there  

[Skinny]

different codes can vary the number of drive cycles to auto clear it. some codes are hard codes and once they are set it's a done deal till it's cleared out.

[littleredbeater]

ok so now it's on solid and here's what I have.

12 Direct battery input to PCM was disconnected within the last 50 Key-on cycles

33 An open or shorted condition detected in the duty cycle purge solenoid circuit.

41 An open or shorted condition in the generator field control circuit.

22 Engine coolant temperature sensor above or below acceptable voltage.

24 Throttle position sensor input above or below acceptable voltage. TPS signal does not correlate to MAP sensor.

it seemed to be related to a rough start up, it runs fine though. any ideas?

[midnightcwby]

Where does your Volt gauge spend most of it's time?.  If your reading somewhere around 13.9 or higher (no lower than 12.5) then your alternator is at least supplying enough voltage for your sensors to work properly (which would mean that the low signal voltage codes you have were not a low charging system voltage problem).  The voltage regulator is built into the back of the alternator, so changing just it isn't very feasible for most people.  

Have you started the engine with the CTS or TPS sensors unplugged (ie. did a TB swap and tried to start the jeep before hooking up the wires or had the CTS sensor disconnected while the engine was running using an ohm meter to test your CTS).  

Not sure why your getting a purge solenoid code... check the wiring going to the purge solenoid to make sure it's ok. The solenoid itself is usually to blame though.

[littleredbeater]

i actually did start the jjep after a tb swap with those two sensors unplugged but shut it off and plugged them back in and it was ok. that was two months ago. could i have damaged something?

[littleredbeater]

OK so on the way home last night my volt gauge was reading about 10, I'm going to spray some brake cleaner in there and see if it's not just dirty brushes but if that doesn't help would you suspect the alternator or the voltage regulator?

[midnightcwby]

No, it won't hurt it. That just explains why you set those two hard codes in memory.  So, you can probably ignore them as you trouble shoot the problem.