basic engine trouble shooting tech
CPS (Crankshaft Position Sensor)
$47ish autozone, can prevent spark at coil, sputtering, stalling while hot, and prevent starting.
Disconnect and check the CPS resistance. Should measure about 275 ohms resistance. Re-connect and Should generate
about 2.5vac when motor is cranking. The CPS is Located at the 10 O'Clock position on the drivers side
top of the transmission housing, held by two 1/2in bolts and feeds up to a 3 pin connector with only
two wires going to the connector. Try unplugging and re-plugging the connection a few times.
If that seems to help, bypass the connection permanently by soldering the wires, use shrink wrap to
insulate the exposed soldered connections.
TPS (Throttle Position Sensor)
special order form checker about $55, can cause hesitation and stalling when retuning to idle, also see EGR
First clean all connector connections and sensor using Carburetor cleaner and electrical contact cleaners.
TO TEST:Use a multi meter to test the three wires. Orientation of the three wires may differ, but one is a ground one, is 5V source,
and one is .75V signal. Do all tests with the engine off and the key in the on position.
First find the ground, put meter on ohms setting, and put one terminal on the clean ground terminal,
the other terminal probe the TPS signal wire. I use T-Taps to tap into the wires so not to hurt the connector. My ground wire showed 15 ohms,
Not great but not TOO bad, Some guys jump this wire to a better ground. Now put your Volt meter on volts setting and
probe your ground on the connector, and look for the 5V source, 4.5V is acceptable. Try with respect to your battery ground also.
Next test your signal for about .75 volts at idle. If it has no voltage at idle its BAD, but if it has the .75 volts, you then need
to slowly move the throttle from idle to open, looking at the voltage to make sure it slowly rises with the
throttle movement upward. If the voltage hops and is not a nice even rise, replace the sensor.
ICA (Ignition Control Actuator) special order from checker, when faulty causes a high idle at like 2000RPMS at start up and will slowly level out.
First clean the throttle body(TB) and ICA sensor with carb cleaner, located next to the TPS on the TB,
Also clean all the connectors.
EGR (Exhause Gas Return) Is a vacuum controlled valve that allows exhaust to circulate back to the intake,
When the diaphragm is ripped or gunked up it may cause stalling at idle. Clean with carb cleaner, $80 ish dealer replacement.
Clean the MAT sensor with carb cleaner if it gets gunked up. Can cause engine stumbling.
clean-running RenixII 4.0 should have about 2.5volts at pin C, if you're running rich you'll have less than that. If you see 5-volts,
then the sensor element is open and they can also short to ground pulling pinC to 0-volts...
NSS, Neutral Safety Switch,
It will cause the starter to not turn over, and if dirty can also cause your backup lights to not work.
ENGINE CODES FOR newer cherokees 91+, older cherokees don't have computer codes:
My Check Engine light is on, how do I access the diagnostic codes?
With the ignition off, switch the key on, off, on, off, on. (This needs to happen in under 5 seconds) Make
sure you don't actually start your Jeep, turn the ignition to the ON position, but do not turn it so far that you start cranking
The check engine light will start to flash, count these flashes. Each code is a two digit number, for example 23 would be
FLASH FLASH <pause> FLASH FLASH FLASH <long pause>
It will never flash more than 9 times, watch for pauses!
Cherokee Engine Diagnostic codes
Start of test (This only appears on DRBII, it's not blinked out)
No ignition reference signal detected during cranking (bad hall effect) OR timing belt skipped one or more
teeth; or intermittent loss of either camshaft or crankshaft position sensor
Memory Standby power lost (battery cable disconnected)
No change in MAP from start to run
MAP sensor circuit open or shorted; voltage too low
No speed/distance sensor signal
Loss of battery voltage detected with engine running
Engine stays cold too long (bad thermostat)
Oxygen sensor signal out of range, possibly shorted
Coolant sensor signal out of range (or disconnected to set timing)
Intake air temperature signal out of range
Throttle position circuit out of range
Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached, vacuum leak found
Peak injector circuit voltage has not been reached
Logic module fuel circuit internal problem or TBI injector does not respond properly to control signal
Evaporator Purge solenoid circuit open or shorted or Evaporator solenoid circuit
EGR system failure or Power loss lamp open or shorted
Air conditioning clutch relay circuit open or shorted
Speed control vacuum or vent solenoid circuits open or shorted
Cooling fan relay circuit open or shorted
Wastegate control circuit open or shorted
Shift indicator light failure, 5-speed (blown bulb) OR Park/neutral switch failure OR Torque converter unlock
circuit open or shorted, A-413 4-speed auto
Alternator field control circuit open or shorted
Automatic shutdown relay circuit open or shorted
Fuel pump relay control circuit
Fuel level unit - no change over miles OR Z1 voltage missing when auto shut-down circuit energized
Peak primary coil current not achieved with max dwell time OR Cylinder misfire
Problem in power module to logic module interface
No FJ2 voltage present at logic board OR Logic module self-diagnostics indicate problem OR Battery
temperature out of range
Turbo boost limit exceeded (engine was shut down by logic module)
Battery voltage too high during charging or charging system voltage too low
Battery voltage too low and alternator output too low
Oxygen sensor stuck at lean position OR Internal logic module fault ('84 turbo only)
Oxygen sensor stuck at rich position OR Internal logic module fault ('84 turbo only)
Logic module internal problem
No sync pickup signal during engine rotation (turbo only) OR Internal logic module fault ('84 turbo only)
55 End of codes
"Baro" sensor open or shorted
EMR mileage cannot be stored in EEPROM
PCM failure SRI mile not stored
Controller cannot write to EEPROM
Catalytic converter efficiency failure
Power steering switch failure