Taken from Cherokee Forum post
1984-1990 w/AMC engine are pre-OBD (Renix)
1984-1986 w/GM V6-173 are OBD-I (GM control setup)
1991-1995 are OBD-I (Chrysler)
1996-2001 are OBD-II (Chrysler)
Taken from NAXJA post
So, before outlining the proceedure (a.k.a. “key trick”) to get the codes, a few things to note:
1) You may have to set the parking brake for the codes to show
2) On older models, the blink-spacing is not always perfectly uniform, so if you see 23 23, it’s probably just a single 55 since codes are not repeated (55 is end of codes – it’s normal)
3) On newer models with a digital odometer, the codes are usually displayed on the odometer rather than blinking the check engine light.
4) When the computer indicates major failure, it can activate “Limp In” mode, which guesses about data to compensate for sensor failure, allowing you to get the car to a mechanic. One major symptom of this is losing third and/or fourth gear on autos.
The “Key Tricks”
Older (OBD-I) models – Start with the ignition off. Within five seconds, switch the key on, off, on, off, on. (“On” is NOT “Start” and “Off” is NOT “Lock”). The “check engine” light will flash. Count the flashes. Each code is a two digit code, so a (for example) 23 would be FLASH FLASH (pause) FLASH FLASH FLASH (long pause). It will never flash more than 9 times, so watch for those pauses!
Newer (OBD-II) models – Put the key into the ignition, push down the odometer reset button, then turn the key to RUN with your finger on the button – and then release the button. The odometer will go through 1111111 through 999999, then display the car’s serial number. It will then show the error codes (it might show them starting with P). If this method does not work, try the OBDI method.
Older Model Computer Codes (OBD-I) – IMPORTANT! Codes may be different for newer vehicles starting circa 1996.
11 No ignition reference signal detected during cranking OR timing belt skipped one or more teeth; OR loss of either camshaft or crankshaft position sensor.
12 Battery or computer recently disconnected
13 MAP sensor or vacuum line may not be working
14 MAP sensor voltage below .16V or over 4.96V
15 No speed/distance sensor signal
16 Loss of battery voltage detected with engine running
17 Engine stays cool too long (bad thermostat or coolant sensor?)
17 (1985 turbo only): knock sensor circuit
21 Oxygen sensor signal doesn’t change (stays at 4.3-4.5V). Probably bad oxygen sensor
22 Coolant sensor signal out of range – May have been disconnected to set timing
23 Incoming air temperature sensor may be bad
24 Throttle position sensor over 4.96V
25 Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached
26 Peak injector circuit voltage has not been reached (need to check computer signals, voltage reg, injectors)
27 Injector circuit isn’t switching when it’s told to (TBI)
OR (MPI) injector circuit #1 not switching right
OR (turbo) injector circuit #2 not switching right
OR (all 1990-) injector output driver not responding
– check computer, connections
31 Bad evaporator purge solenoid circuit or driver
32 (1984 only) power loss/limited lamp or circuit
32 EGR gases not working (1988) – check vacuum, valve
32 (1990-92) computer didn’t see change in air/’fuel ratio when EGR activated – check valve, vacuum lines, and EGR electrical
33 Air conditioning clutch relay circuit open or shorted (may be in the wide-open-throttle cutoff circuit or normal on early 80’s models if you don’t have air conditioning)
34 (1984-86) EGR solenoid circuit shorted or open
34 (1987-1991) speed control shorted or open
35 Cooling fan relay circuit open or shorted
35 idle switch motor fault – check connections
36 (turbo only) Wastegate control circuit open or shorted
37 Shift indicator light failure, 5-speed
part throttle lock/unlock solenoid driver circuit (87-89)
solenoid coil circuit (85-87 Turbo only)
Trans temperature sensor voltage low (1995 and on)
41 Alternator field control circuit open or shorted
42 Automatic shutdown relay circuit open or shorted
42 Fuel pump relay control circuit
42 Fuel level unit – no change over miles
42 Z1 voltage missing when autoshutdown circuit energized (The Z1 voltage is the voltage of the circuits fed by the autoshutdown relay. This typically includes fuel pump and switched-battery feed to the ignition coil)
43 Peak primary coil current not achieved with max dwell time
43 Cylinder misfire
43 Problem in power module to logic module interface
44 No FJ2 voltage present at logic board
44 Logic module self-diagnostics indicate problem
44 Battery temperature out of range
45 Turbo boost limit exceeded (engine was shut down by logic module)
46 Battery voltage too high during charging or charging system voltage too low
47 Battery voltage too low and alternator output too low
51 Oxygen sensor stuck at lean position (this may be tripped by a bad MAP sensor system causing a rich condition. If you get hot rough idle and stalling, especially on deceleration, accompanied by flooded engine and difficulty restarting, that can be a bad MAP sensor causing the O2 sensor to try to compensate. If you get poor cold driveability, stumbling and bucking, and acceptable warm driving with poor gas mileage (a drop of 10 mpg or more), that is usually the O2 sensor.
51 Internal logic module fault (’84 turbo only).
52 Oxygen sensor stuck at rich position
52 Internal logic module fault (’84 turbo only)
53 Logic module internal problem
54 No sync pickup signal during engine rotation (turbo only)
54 Internal logic module fault (’84 turbo only) – or camshaft sensor/distributor timing
55 End of codes
61 “Baro” sensor open or shorted
62 EMR mileage cannot be stored in EEPROM
62 PCM failure SRI mile not stored
63 Controller cannot write to EEPROM
64 Catalytic converter efficiency failure
65 Power steering switch failure
Newer model Computer codes (OBDII)
30 Sensor heater relay problem
36 Sensor heater relay problem
106 MAP sensor voltage out of range detected at startup
107 MAP sensor voltage too low
108 MAP sensor voltage too high
112 Intake air temperature sensor voltage low
113 Intake air (charge) temperature sensor voltage high
116 Coolant temparature sensor reading doesn’t make sense
117 Engine coolant temperature sensor voltage low
118 Engine coolant temperature sensor voltage high
121 Throttle position sensor and MAP sensor disagree with each other
122 Throttle position sensor voltage low
123 Throttle position sensor voltage high
125 Taking too long to reach proper operating temparature and switch to energy-efficient mode
130 Sensor heater relay problem
131 Oxygen sensor seems to be shorted out or broken
147 Oxygen sensor heater element not working properly (this device helps to reduce emissions more quickly)
151 Oxygen sensor voltage problem – short circuit to ground?
152 Oxygen sensor voltage problem – short circuit to active 12V?
153 Oxygen sensor response too slow
154 Oxygen sensor does not show either a rich or lean condition – may need replacement
155 Oxygen sensor heater element not working properly (this device helps to reduce emissions more quickly)
157 Oxygen sensor voltage problem – short circuit to ground?
158 Oxygen sensor voltage problem – short circuit to active 12V?
159 Oxygen sensor response too slow
160 Oxygen sensor does not show either a rich or lean condition – may need replacement
161 Oxygen sensor heater element not working properly (this device helps to reduce emissions more quickly)
171 The oxygen sensor is saying that the system air/fuel mix is far too lean (too much fuel is being added as a correction).
172 The oxygen sensor is saying that the system air/fuel mix is far too rich (too much air is being added as a correction).
174 The oxygen sensor is saying that the system air/fuel mix is far too lean (too much fuel is being added as a correction).
175 The oxygen sensor is saying that the system air/fuel mix is far too rich (too much air is being added as a correction).
176 Flex fuel sensor can’t be seen
178 Flex fuel sensor problem
179 Flex fuel sensor problem
182 Compressed natural gas temperature sensor problem
183 Compressed natural gas temperature sensor problem
201 Injector #1 control circuit problem (open or shorted)
202 Injector #2 control circuit problem (open or shorted)
203 Injector #3 control circuit problem (open or shorted)
204 Injector #4 control circuit problem (open or shorted)
205 Injector #5 control circuit problem (open or shorted)
206 Injector #6 control circuit problem (open or shorted)
207 Injector #7 control circuit problem (open or shorted)
208 Injector #8 control circuit problem (open or shorted)
300 Misfire detected in multiple cylinders.
301 Misfire detected in cylinder #1.
302 Misfire detected in cylinder #2.
303 Misfire detected in cylinder #3.
304 Misfire detected in cylinder #4.
305 Misfire detected in cylinder #5.
306 Misfire detected in cylinder #6.
307 Misfire detected in cylinder #7
308 Misfire detected in cylinder #8.
320 Crankshaft position sensor reference signal cannot be found while the engine is cranking.
325 Knock sensor (#1) signal is wrong.
330 Knock sensor (#2) signal is wrong.
340 No camshaft signal being received by the computer
350 A coil is drawing too much current.
351 Coil #1 is not reaching peak current at the right time
352 Coil #2 is not reaching peak current at the right time
353 Coil #3 is not reaching peak current at the right time
354 Coil #4 is not reaching peak current at the right time
355 Coil #5 is not reaching peak current at the right time
356 Coil #6 is not reaching peak current at the right time
357 Coil #7 is not reaching peak current at the right time
358 Coil #8 is not reaching peak current at the right time
401 A required change in air/fuel mixture was not detected during diagnostic test.
403 An problem was detected in the EGR solenoid control circuit.
404 The EGR sensor’s reported position makes no sense
405 EGR position sensor voltage wrong.
406 EGR position sensor voltage wrong.
412 The secondary air solenoid control circuit seems bad (this is used for the aspirator).
420 The catalyst seems inefficient (#1).
432 The catalyst seems inefficient (#2).
441 Evaporative purge flow system not working properly
442 A leak has been detected in the evaporative system!
443 Evaporative purge flow system solenoid not working properly
455 A large leak has been detected in the evaporative system!
456 A small leak has been detected in the evaporative system!
460 The fuel level sender is not reporting any change over a long distance. Something seems wrong.
461 The fuel level sender is not reporting any change over a long time. Something seems wrong.
462 Fuel level sender voltage wrong.
463 Fuel level sender voltage wrong.
500 Haven’t heard from the speed sensor lately.
505 The idle speed air control motor doesn’t seem to be working correctly.
522 Oil pressure sensor problems
523 Oil pressure sensor problems
551 The power steering switch may not be working. (Neons: high pressure is showing up at high speed)
600 Oh-oh! The coprocessors aren’t talking to each other within the computer!
601 Internal computer error!
604 Internal computer error! (RAM check)
605 Internal computer error! (ROM)
615 Starter relay circuit problem
622 Generator field control problem
645 A/C clutch relay circuit problem.
700 The automatic transmission computer or Aisin computer has a problem – ask it what’s going on. I don’t know.
703 Brake switch circuit information seems wrong.
711 Based on the transmission temperature and its operations, it looks like the transmission temperature sensor’s gone bad.
712 Transmission fluid temperature sensor voltage wrong.
713 Transmission fluid temperature sensor voltage wrong.
720 The Output Shaft Speed Sensor doesn’t match the reported vehicle speed.
740 The engine’s running faster than it should for these speeds, so I think thetorque convertor clutch lock-up system is bad
743 Torque converter clutch (part throttle unlock) solenoid circuit problem – shift solenoid C electrical fault
748 Governor Pressure Solenoid circuit problem (Transmission relay circuit problem in Jeep RE transmissions)
751 Overdrive override switch has been pressed for over five minutes. Just thought you should know.
753 Overdrive solenoid control circuit problem (transmission relay circuit in Jeep RE transmissions.)
756 Shift solenoid B (2-3) fault
783 The overdrive solenoid can’t go from 3rd gear to the overdrive gear.
801 Transmission reverse gear lockout solenoid circuit problem!
833 Problem with the clutch-released switch circuit?
1192 Inlet air temperature sensor voltage is wrong
1193 Inlet air temperature sensor voltage is wrong
1194 Oxygen sensor heater performance is faulty
1195 Oxygen sensor is slow
1196 The oxygen sensor switched too slowly (bank 2).
1197 The oxygen sensor switched too slowly (bank 1).
1198 Radiator coolant temperature sensor voltage is wrong.
1199 Radiator coolant temperature sensor voltage is wrong.
1281 The engine is staying cold too long – check your thermostat.
1282 The fuel pump relay circuit seems to be having a problem.
1288 The intake manifold short runner tuning valve circuit seems to be having a problem.
1289 There’s a problem in the manifold tuning valve solenoid control circuit.
1290 Compressed natural gas system pressure is too high
1291 The heated air intake sensor does not seem to be working.
1292 Natural gas pressure sensor issue
1293 Natural gas pressure sensor issue
1294 Can’t get to target engine speed, check for vacuum leaks and idle speed motor issues.
1295 The throttle position sensor doesn’t seem to be getting enough electricity.
1296 The MAP sensor doesn’t seem to be getting enough electricity.
1297 The MAP sensor doesn’t change its reading when the engine is running!
1298 During wide-open throttle, the engine runs lean.
1299 MAP Sensor and Throttle Position Sensor signals don’t match, check for a vacuum leak.
1388 Auto shutdown relay circuit problems?
1389 No Z1 or Z2 voltage seen by the computer when the auto shutdown relay is used.
1390 Cam and crank signals don’t match – did the timing belt skip a tooth?
1391 Sometimes, I can’t see the crank or cam sensor signal.
1398 I can see the Crank Sensor’s signal when I prepare for Misfire Diagnostics. Try replacing it.
1399 Problem in the Wait to Start Lamp circuit – (diesels only?)
1403 EGR position sensor not getting (enough) voltage.
1476 Too little secondary air injection during aspirator test.
1477 Too much secondary air injection during aspirator test.
1478 Battery temperature sensor voltage wrong.
1479 Transmission fan relay circuit problems?
1480 PCV solenoid circuit problems?
1481 Transmission RPM pulse generator signal for misfire detection seems wrong.
1482 Catalyst temperature sensor circuit shorted low.
1483 Catalyst temperature sensor circuit shorted high.
1484 The catalyst seems to be overheating!
1485 Air injection solenoid circuit problems.
1486 Pinched or blocked hose in the evaporative hose system.
1487 Control circuit of the #2 high-speed radiator fan control relay is having problems.
1488 Auxiliary 5-volt sensor feed is too low.
1489 High speed radiator fan control circuit problem.
1490 Low speed radiator fan control circuit problem.
1491 Radiator fan control circuit problem (may be solid state relays as well as other circuits).
1492 Ambient or battery temperature sensor voltage wrong
1493 Ambient or battery temperature sensor voltage wrong
1494 Leak Detection Pump (LDP) pressure switch problem – electrical or the pump itself.
1495 Leak Detection Pump (LDP) pressure switch problem – the solenoid circuit.
1496 Sensor feed is below an acceptable limit. (under 4v for 4 seconds – should be 5v).
1498 High speed radiator fan control circuit problem. (#3 control relay)
1594 Voltage too high in charging system.
1595 Speed control vacuum or vent solenoid control circuits shorted or lost.
1596 Speed control switch always high
1597 Speed control switch always low
1598 A/C pressure sensor voltage high
1599 A/C pressure sensor voltage low
1681 No messages received from the cluster control module (dashboard computer).
1682 Charging system doesn’t seem to be working well. Check alternator, etc.
1683 Speed control servo power control circuit problem.
1684 The battery has been disconnected within the last 50 starts.
1685 Invalid key received from the Smart Key Immobilizer Module.
1686 No messages received from the Smart Key Immobilizer Module.
1687 No messages received from the Mechanical Instrument Cluster module.
1 693 The companion engine control module has shown a fault.
1694 No messages received from the powertrain control module-Aisin transmission.
1695 No messages received from the body control module.
1696 Unsuccessful attempt to write to an EEPROM location!
1697 Unsuccessful attempt to update Service Reminder Indicator (SRI or EMR) mileage!
1698 No messages received from the electronic transmission control module or the Aisin transmission controller.
1719 Transmission 2-3 gear lockout solenoid control circuit problem.
1740 Either the tcc solenoid or overdrive solenoid systems doesn’t seem to be making much sense.
1756 Transmission control pressure not equal to target. (Mid pressure problem)
1757 Transmission control pressure not equal to target. (Zero pressure problem)
1762 The Governor Pressure Sensor input was too high or too low for 3 consecutive park/neutral calibrations.
1763 The Governor Pressure Sensor input is too high
1764 The Governor Pressure Sensor input is too low.
1765 Open or short in the Transmission Relay control circuit.
1899 The Park/Neutral switch seems to be stuck!