tatuedrednek
Wanderer
Sure have, all to no avail. I have done some more digging and am still coming up with nothing. I sure love computer controlled engines!
Cherokee ECM problems.
- Thread starter tatuedrednek
- Start date
BIGdaddy
Expedition Leader
1stDeuce
Explorer
Sounds like the data buss wire from the ECM to the ALDL connector might be bad, or not making contact at one end or the other. That would be supported by the new ECM you tried also having connectivity issues with the scan tool. Even if that's the case, the check engine light trick should work on your '96. I found one site saying that for the '96-97 you need 4 cycles, not 3. (on-off-on-off-on-off-on) It may take a bit of time for the light to start flashing according to some of the sources, so give it 20 seconds or so after the final "on". If you cycle the key too fast or too slow, I don't think it'll work either. About a half second or so in each position, like you're reading it s-l-o-w. 
Here's a youtube clip that starts just after the last "on". You can watch the Maint Req and CEL both clear, then it flashes the codes. 12, 72, 55.
To approach it from another angle, if you unplug the ECM or disconnect the battery to clear codes, does the light come on right away when you start the engine, or after the engine has been running for a few minutes, or only after several drive cycles?? That alone can tell you what sort of problem you're looking for. Several drive cycle problems are generally emissions related, and I'd suggest looking at oxygen sensors or perhaps for a plugged cat. Immediate on lights are shorted or open sensor inputs, and you could check wiring to sensors.
Good luck!
Here's a youtube clip that starts just after the last "on". You can watch the Maint Req and CEL both clear, then it flashes the codes. 12, 72, 55.
To approach it from another angle, if you unplug the ECM or disconnect the battery to clear codes, does the light come on right away when you start the engine, or after the engine has been running for a few minutes, or only after several drive cycles?? That alone can tell you what sort of problem you're looking for. Several drive cycle problems are generally emissions related, and I'd suggest looking at oxygen sensors or perhaps for a plugged cat. Immediate on lights are shorted or open sensor inputs, and you could check wiring to sensors.
Good luck!
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tatuedrednek
Wanderer
Thanks for the info. The broken wire I talked about earlier was the bus wire. It had shorted to ground but is repaired now. And for the record, O2 sensors are both functioning correctly. This light is really more of a nuisance than anything, but being a mechanic I have enough sense to fix the problem as opposed to putting a band-aid on it.
tatuedrednek
Wanderer
No chance of that. Soldered and heat shrinked! And now it has continuity!
1stDeuce
Explorer
Did you try the 3 or 4 off-on's again??? That really SHOULD work on your jeep as far as I know... ???
It's possible you fried the buss msg generator in your ECM when it grounded, but not likely. Did you try the new ECM after you fixed it, or before?
And how long does it take for the light to come back on after you disconnect the battery to clear codes?
C
It's possible you fried the buss msg generator in your ECM when it grounded, but not likely. Did you try the new ECM after you fixed it, or before?
And how long does it take for the light to come back on after you disconnect the battery to clear codes?
C
BIGdaddy
Expedition Leader
On-off-on-off-on, sometimes with an extra off-on though. The engine should be fully warmed up; I couldn't get mine to pull codes after driving around the block but it worked after the 65 mile drive to work. http://allpar.com/fix/codes.html
____________________________________________________________
From here:
http://www.naxja.org/forum/showthread.php?t=27505
Later in the thread they talk about a specific type of scanner:
____________________________________________________________
Pep boys has an Actron OBDII code reader on-sale for $99 until 6-12.
With four OBDII vehicles, I finally gave up and bought one. It shows more codes than what can be read with just the flashing lights. It is especially handy when an engine has multiple trouble codes.
____________________________________________________________
From here:
http://www.naxja.org/forum/showthread.php?t=27505
Later in the thread they talk about a specific type of scanner:
____________________________________________________________
Pep boys has an Actron OBDII code reader on-sale for $99 until 6-12.
With four OBDII vehicles, I finally gave up and bought one. It shows more codes than what can be read with just the flashing lights. It is especially handy when an engine has multiple trouble codes.
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tatuedrednek
Wanderer
I put the new ecm in after repairing the broken wire. To no avail. Unfortunately life has gotten in the way of spending much more time on this. I have tried the key trick and nothing. For now a small piece of electrical tape, over the light, has fixed it. Hopefully I'll have some more time the coming weeks to chase this problem some more. Thanks everyone for all the free advice!