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Start with the ignition off. Within five seconds, switch the key on, off, on, off, on. (On is *not* start!)
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 (loong pause)
It will never flash more than 9 times, watch for pauses! 55 is end of codes, 33 is normal if you don't have air conditioning.
When the computer indicates major failure, it will activate Limp In mode, which guesses about data to compensate for sensor failure.
Please note that some codes are NOT included below, this is not a complete listing, but it IS very close to complete. Most of it comes from the Mopar Mailing List.
* Activates Power Limited/Check Engine light on some models.
17 Engine stays cool too long (bad thermostat or coolant
sensor?)
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 (SEE NOTE #3)
25 Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached, vacuum leak found
26 Peak injector circuit voltage has not been reached (need to check computer signals, voltage reg, injectors) (SEE NOTE #4 BELOW)
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, all but Turbo) 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)
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 (trucks) idle switch motor fault - check connections
36 (turbo) Wastegate control circuit open or shorted
36 (3.9/5.2 RWD) solenoid coil circuit (air switching)
36 (Turbo IV) #3 Vent Solenoid open/short
37 Shift indicator light failure,
5-speed
OR
part throttle lock/unlock solenoid driver circuit (87-89)
OR
solenoid coil circuit (85-89 Turbo I-IV)
OR
Trans temperature sensor voltage low (1995 and on; see
NOTE 2)
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
OR
42 Z1 voltage missing when autoshutdown circuit energized (SEE NOTE #6)
43 Peak primary coil current
not achieved with max dwell time
OR
43 Cylinder misfire
OR
43 Problem in power module to logic module interface
44 No FJ2 voltage present at
logic board
OR
44 Logic module self-diagnostics
indicate problem
OR
44 Battery temperature out of range (see Note #1!)
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 (lean condition)
OR
51 Internal logic module fault ('84 turbo only)
52 Oxygen sensor stuck at rich
position (SEE NOTE #5!)
OR
52 Internal logic module fault ('84 turbo only)
53 Logic module internal problem
54 No sync pickup signal during
engine rotation (turbo only)
OR
54 Internal logic module fault ('84 turbo only)
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
88 Start of test (not usually given, don't expect it)
The problem may be cured with tuner cleaner on the connectors.
For TBI engines, the injector's cold resistance should
be between 0.9 and 1.2 ohms (specs vary with year). This is a peak-and-hold
injector. With the engine idling the peak period should be about 1.2 milliseconds
whereas the hold period will vary. If it's lower than this at idle, then
the injector's shorted or there's a defect in the injector driver circuit.
(Bohdan Bodnar)
I've used the Z1 voltage to test for good power connections
to the power module. I connected my OTC 500 multimeter from the battery's
positive post to the ignition coil's switched battery terminal and measured
the voltage drop using the bar graph to monitor peak voltages. Voltage
spikes of around 200 mV to 300 mV are ok -- anything more means tv tuner
cleaner time (or replacing the power module). Another thing to check is
the maximum voltage drop during the priming pulse. With the old power module,
I was losing about 2 volts across the circuit; the replacement is losing
about 1/4 volt. (Thanks, bbodnar@lucent.com)