Jeep Cherokee Check Engine Light Codes.

Jeep Cherokee Check Engine Light Codes.

On the 91 to 96 Jeep Cherokees the ECU codes are accessible by watching the Check engine light blink on the dash. You cycle the key on and off three times leaving it on but not starting the Jeep. The codes will begin to flash on the dash light. Count the flashes and note the pause between flashes. For example the first code will usually be a 12. The light will blink once then pause and then blink twice more. The last code is always a 55.

Below are the instructions from the FSM on how to get the codes. Below that is the chart of what the codes mean. This chart was taken from the 94 FSM but all the HO engines will be similar.

ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be displayed by cycling the ignition key On-Off-On-Off-On within three seconds and observing the Malfunction Indicator Lamp. This lamp was formerly referred to as the Check Engine Lamp. The lamp is located on the instrument panel.

11 * No Crank Reference Signal at PCM No crank reference signal detected during engine cranking.
12 * Battery Disconnect Direct battery input to PCM was disconnected within the last 50 Key-on cycles.
13 ** No Change in MAP From Start to Run No difference recognized between the engine MAP reading and the barometric (atmospheric) pressure reading at start-up.
14 ** MAP Sensor Voltage MAP sensor input below minimum acceptable voltage.
or
MAP sensor input above maximum acceptable voltage.
15 ** No Vehicle Speed Sensor Signal No vehicle distance (speed) sensor signal detected during road load conditions.
17 * Engine is Cold Too Long Engine coolant temperature remains below normal operating temperatures during vehicle travel (thermostat).
21 ** O2S Stays at Center Neither rich nor lean condition detected from the oxygen sensor input.
or
O2S Shorted to Voltage Oxygen sensor input voltage maintained above the normal operating range.
22 ** ECT Sensor Voltage Engine coolant temperature sensor input above maximum acceptable voltage.
or
Engine coolant temperature sensor input below minimum acceptable voltage.
23 ** Intake Air Temp Sensor
Voltage Low Intake air temperature sensor input below the minimum acceptable voltage.
or
Intake air temperature sensor input above the maximum acceptable voltage.
24 ** Throttle Position Sensor
Voltage Throttle position sensor input above the maximum acceptable voltage.
or
Throttle position sensor input below the minimum acceptable voltage.
25 ** Idle Air Control Motor
Circuits A shorted condition detected in one or more of the idle air control motor circuits.
27 * Injector Control Circuit Injector output driver does not respond properly to the control signal.
33 * A/C Clutch Relay Circuit An open or shorted condition detected in the A/C clutch relay circuit.
34 * Speed Control Solenoid
Circuits An open or shorted condition detected in the Speed Control vacuum or vent solenoid circuits.
or
Speed Control Switch Always Low
Speed Control switch input below the minimum acceptable voltage.
or
Speed Control Switch Always High
Speed Control switch input above the maximum acceptable voltage
35 * Rad Fan Control Relay
Circuits An open or shorted condition detected in the radiator fan relay circuit.

41 ** Generator Field Not
Switching Properly An open or shorted condition detected in the generator field control circuit
42 * Auto Shutdown Relay
Control Circuit An open or shorted condition detected in the auto shutdown relay circuit.
44 * Battery Temp Sensor
Volts out of Limit An open or shorted condition exists in the engine coolant temperature sensor circuit or a problem exists in the PCM’s battery temperature voltage circuit.
46 ** Charging System Voltage
Too High Battery voltage sense input above target charging voltage during engine
Operation
47 ** Charging System Voltage
Too Low Battery voltage sense input below target charging during engine operation.
Also, no significant change detected in battery voltage during active test of generator output.
51 ** O2S Signal Stays Below Center (Lean) Oxygen sensor signal input indicates lean air/fuel ratio condition during engine operation.
52 ** O2S Signal Stays Above Center (Rich) Oxygen sensor signal input indicates rich air/fuel ratio condition during
engine operation
53 * Internal PCM Failure
Or
PCM Failure SPI Communications PCM Internal fault condition detected.
or
PCM Internal fault condition detected.
54 * No Cam Sync Signal at
PCM No fuel sync (camshaft signal) detected during engine cranking.

55 . N/A Completion of diagnostic trouble code display on the Malfunction Indicator Lamp (Check Engine Lamp).
62 * PCM Failure SPI miles not stored Unsuccessful attempt to update SPI miles in the PCM EEPROM.

63 * PCM Failure EEPROM
Write Denied Unsuccessful attempt to write to an EEPROM location by the PCM.

* Check Engine Lamp will not illuminate at all times if this Diagnostic Trouble Code was recorded. Cycle Ignition key as described in manual and observe code flashed by Check Engine lamp.
** Check Engine Lamp will illuminate during engine operation if this Diagnostic Trouble Code was recorded.