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Check Engine Light Not Functioning

Q

QuillsXJ

NAXJA Forum User
Location
California
So I have the opposite problem as most on this forum: my check engine light will not come on! When I turn the key to on the light never illuminates. I need ideas on how to trouble shoot this. I have swapped the bulb in the dash with a known working one and still nothing. The light not working is an instant fail when I go to Smog. Jeep is running perfectly and starts just fine. Thanks!

I6, Automatic, OBD-II, '98 XJ
 
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Yeah

P0700 = Transmission Control System Malfunction
P0740 = Torque Converter Clutch Circuit Malfunction

I cleared the codes with a scanner and did a full re-boot on the ECU by pulling the battery and the codes came back or maybe never cleared. I have owned the Jeep for about three weeks and I have never seen the check engine light come on.
 
Well, all the gauges and lights are controlled via the CCD bus. So, with codes on the system, a known good bulb installed and it not even coming on at key-on, that is a strong indicator that the cluster has failed. It is possible the bulb socket is faulty too.
 
You can do a IP actuator test as follows

Turn ignition off.
hold down trip reset button, turn ignition switch on, do not start engine, release the button.

CEL should stay off for 6 seconds, come on for 8, off 2 on 2 then off.

other lights will be similar acting and the gauges will do their thing
 
I noticed also that in the IOD section of my PDC I am missing several fuses and when I got the Jeep the PDC wasn't clipped into place, but rather sitting loose near the bracket. Should all the IOD or small fuses be filled in the PDC if it's indicated as having one on the PDC lid? Do you have a diagram of what these unlabeled fuses go to?

Edit: If only the CEL fails to do anything during the IP (I apologize, what does IP stand for?) test what will that tell me?
 
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unlabeled usually means no fuse goes there.

i do not have the means of posting diagrams from my source... a Google search should come up with something.
 
IP = Instrument Panel

If the bulb does not illuminate during the IP test it will help you isolate whether you have a bad cluster, or a deeper problem. The function of the IP test as descrbed by Digger87XJ is to determine whether the gauges and dash lights are operating correctly, outside of their normal PCM control.

Ex: You run out of fuel with the guage reading 1/2 full. A sweep of the gauge cluster will show you whether the gauge can operate correctly to the full position. This will help the technician remove the gauge as suspect during diagnosis.

FYI, replacement clusters are readily available and are a direct bolt in, although you will retain the mileage of the swapped cluster unless you have it re-programmed or attempt to re-program it yourself. There are several threads on this topic. I completed the swap for $40 in 10 minutes (wasn't concerned with mileage).
 
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Sounds to me like someone knew about the trans codes and disabled the light to dump the truck.

Look for tampering with the socket/connections.

The worse part is you'll still fail until you get the trans codes repaired.

Ps the tcc solenoid is about $163 from rockauto.com .
 
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I sure don't know if the 98 is the same as my 96, but I had a partlal short in my 5 volt sensor supply circuit on two seperate occasions, for two different problems and both times my CEL went out and refused to light up when the key was turned to run.

I found the issue by accident when I unplugged the offending sensor and the CEL came back on. I did a volt test and found 3 volts in the 5 volt sensor circuit with the shorted sensor plugged up.
 
I did the IP light test last night and the CEL never came on. I also unplugged the TCU and PCM and cleaned and reseated all connections. I again confirmed that all fuses in the PDC and the interior fuse box are not open and intact.

Before bed, kind of frustrated, I was skimming my Chilton's manual and I came across this (page 4-15):



I thought for sure this or the similar thought process was going to identify where the problem was, so when I went to start this process and find diagnostic connector D-2 I learned that this connector doesn't exist on the 98. Is it possible to incorporate this similar flow chart into the 98 Cherokee? Is there a connector I could jumper the ground to CEL pin to bypass the PCM or something of the like?

I am less than an hour away from caving and just buying a new PCM. :(

8Mud: I am curious, which sensors in particular were you having a short with? Did your Jeep still run perfect regardless of these sensors being shorted?
 
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Oh lol okay well that changes things a bit (cost, etc.). For clarity, I can rule out the possibility of a shorted sensor as 8Mud stated then?

Edit: When I get a working cluster does the odometer have to be re-programmed for my mileage or does it display the value stored on the PCM?
 
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98NWCherokee said:
FYI, replacement clusters are readily available and are a direct bolt in, although you will retain the mileage of the swapped cluster unless you have it re-programmed or attempt to re-program it yourself. There are several threads on this topic. I completed the swap for $40 in 10 minutes (wasn't concerned with mileage).
Click to expand...

QuillsXJ said:
Oh lol okay well that changes things a bit (cost, etc.). For clarity, I can rule out the possibility of a shorted sensor as 8Mud stated then?

Edit: When I get a working cluster does the odometer have to be re-programmed for my mileage or does it display the value stored on the PCM?
Click to expand...
 
X2.
The IP has a failure.
 
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