This generation Jeep doesn't require a special diagnostics scanner. This is a plus, because you don’t need any expensive tools to figure out what’s ailing your Jeep
Using the ignition switch, at no point do you actually start the Jeep: Start with the ignition in the OFF position, turn the key to ON, OFF, ON, OFF, ON ... stop .. leave the key in the ON position (Complete this sequence in under 5 seconds). Once you stop the key in the ON position, the check engine light will stay lit for a moment. When the light goes off, get ready to start counting the light flashings.
Once the Check Engine Light has turned off, it will pause in the off position for a second or two, and then start to flash, count the flashes. Each code stored will be given to you in a 2 digit sequence. As an example, code 43 would be FLASH FLASH FLASH FLASH... <PAUSE>... FLASH FLASH FLASH followed by a <LONG PAUSE>, followed by the next code. There will never be more than 9 flashes without a pause, and finally Code 55 signals the end of stored codes. You can repeat the key sequence as many times as needed if you were unsure of a code.
*= Check Engine light will not illuminate at all times if this Trouble Code it present.
**= Check Engine light will illuminate during engine operation if this Trouble Code is present.
Diagnostic trouble code and descriptions:
11*: No crank reference signal detected during cranking. Timing chain skipped one or more teeth; or intermittent loss of either camshaft or crankshaft position sensor
12*: Battery or computer recently disconnected within the last 50 start cycles). This is a very common code. Will not trigger a "Check engine light".
13**: No change in Manifold Absolute Pressure sensor (MAP) from start to run
14**: MAP sensor voltage too high or too low
15**: No speed sensor signal detected
17*: Engine stays cold too long. Bad thermostat or temp sensor
21**: Oxygen sensor detection neither rich or lean -
21**: Oxygen sensor input voltage stayed above normal operating range
22**: Coolant temperature sensor signal above or below acceptable voltage
23**: Intake air temperature sensor signal above or below acceptable voltage
24**: Throttle position sensor signal above or below acceptable voltage
25**: Automatic Idle Speed (AIS) motor driver circuit shorted
27*: One of the Injectors output drivers does not respond properly to control signal
33*: Air conditioning clutch relay circuit open or shorted. If your Jeep doesn't have AC you will always get this code. Will not trigger a "Check engine light".
34*: Speed control vacuum or vent solenoid circuits open or shorted. Switch is above or below acceptable voltage
35*: (XJs only) Cooling fan relay circuit open or shorted
37: Relationship between engine speed and vehicle speed indicates no torque converter clutch engagement. An open or shorted condition detected in the torque converter part throttle unlock solenoid control circuit. Incorrect input state detected for the Park/Neutral switch. Auto only.
41**: Alternator field control circuit open or shorted
42*: An open or shorted condition detected in the auto shutdown relay circuit. An open condition detected in the ASD relay output circuit. An open or shorted condition detected in the fuel pump relay control circuit. An open circuit between PCM and fuel gauge sending unit. Circuit shorted to voltage between PCM and fuel gauge sending unit. No movement of fuel level sender detected
43: Peak primary circuit current not achieved with maximum dwell time. Misfire detected in one or more cylinders 1 thru 6. (4 and 6 cyls.)
44*: Open or shorted condition in the engine coolant temp sensor circuit or a problem exists in the PCMs battery temp voltage circuit.
46**: Battery voltage too high during charging
47**: Battery voltage sense input below target charging during engine operation. Also, no significant change detected in battery voltage during active test of generator output circuit
51**: A rich air/fuel mixture has been indicated by an abnormally rich correction factor
52**: A rich air/fuel mixture has been indicated by an abnormally rich correction factor.
53*: PCM module internal problem
55*: PCM has finished telling you the codes. This means you are done reading codes.
62: EMR mileage cannot be stored in EEPROM
62: PCM failure SPI mile not stored
63*: Controller cannot write to EEPROM
64: Catalytic converter efficiency failure
65: Power steering switch failure
****This information was gotten from the Chrysler FSM, Quadratec & various posts on WranglerBoard forum. So, I can’t and will not promise or guarantee it’s complete accuracy. Diagnosing trouble codes and changing parts can still be like chasing a needle in a haystack. But, it’s always a good place to start.