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42 Computer Codes


This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.

42 Computer Codes

THESE ONLY WORK IF YOU HAVE FUEL INJECTION. Otherwise, see the web site or
the "troubleshooting electronic feedback carburetors" section.

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.


See http://www.ptcruizer.com/computer-codes.html for a new, revised list of
computer codes and instructions on how to get them. These codes appear to
have been phased in starting in around 1998.


Please note that some codes are NOT included below, this is not a complete
listing. (From Herb with additions by Charles Hobbs. Basis: Mopar Mailing
List info.)

* Activates Power Limited/Check Engine light.

11 No ignition reference signal detected during cranking (bad Hall
OR timing belt skipped one or more teeth;
OR loss of either camshaft or crankshaft position sensor
12 Battery or computer recently disconnected
- Fraser Shortt said code 12 appeared with some other codes
in 1989 and possibly later computers as well.
13* MAP sensor or vacuum line may not be working
14* MAP sensor voltage below .16V or over 4.96V

NOTE - on early Neons, a computer error may light the Check Engine light and
show one or more of these codes. If this happens, bring it in so the dealer
reprogram the computer (about ten minutes).

15 No speed/distance sensor signal
16* Loss of battery voltage detected with engine running
17 (1985 turbo only): knock sensor circuit
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)
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
part throttle lock/unlock solenoid driver circuit (87-89)
solenoid coil circuit (85-89 Turbo I-IV)
Trans temparature 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
42 Z1 voltage missing when autoshutdown circuit energized (SEE NOTE #6)
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 (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)
51 Internal logic module fault ('84 turbo only)
52 Oxygen sensor stuck at rich position (SEE NOTE #5!)
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)
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 given on most computers)

NOTE #1.

The power module has an air-cooled resistor which senses incoming air
temperature. The logic modules uses this information to control the field
current in the alternator. This code applies ONLY to alternators whose
voltage is computer regulated. If you lose the feed to keep RAM
information stored
when the engine's off, you also lose battery voltage sensing. Bohdan Bodnar


From the 1995 TRUCK manuals: the trailer towing package includes a
transmission coolant temp sensor while the standard package doesn't.
This may cause the low (no) voltage indication. J.E. Winburn


Matt Rowe comments: The throttle
postion circuit tells the computer how far the accelerator is depressed.
The Throttle Position Sensor (TPS) is on the throttle body on
the opposite side of the throttle cable. The connector should
have a round rubber cover over the connections. Clear the fault
codes, start the car and try jiggling the wires/connectors to try
to trip a fault code. Loss of this signal could cause other problems.


During cranking, the computer will test the current through the
injector to see whether there's too much resistance in the injector's
path. If there is, code 26 is set.
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)


Wade Goldman wrote: In my case, the breather tube leading into the
catalytic converter had rusted and become detached. This some how would
cause the sensor to read an over rich condition and run crummy. I did not
trust the reliability of the weld over a corroded surface and opted for
the more expensive route of replacing the converter, breather tube and all.


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(s). In my Le Baron, the Z1 circuit leaves the power module
and splits into two paths: the fuel pump and the positive side of the
ignition coil. Internal to the power module is the auto shutdown relay (in
my case, it's a sealed box about 1" by 1"). The output voltage is
monitored to determine whether the relay responds correctly. I suspect
that the ASD relay (and, therefore, the Z1 circuit) also feeds the fuel
injector(s) driver(s) and current sensing circuit, but can't prove this.

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, Bohdan Bodnar)


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