When a late-model, computerized Jeep is having engine problems, one of the ways it communicates these problems back to the driver is to turn on the “check engine” light on the dash. One idiot light isn’t very descriptive, so Jeep also provided a method to query the computer for all codes that have been set. Some of these codes are important enough to turn on the check engine light, while others are minor enough not to require immediate attention and therefore will not turn on the dashboard light by themselves.
To query and OBD-I-era computer for these codes, put the key in the ignition and turn the key to run (not start), then off, then run, then off, then run (that’s 3 runs and 2 offs). Leave the key in the run position. The check engine light will turn on for a few seconds, then turn off, then (sometimes after 20-30 seconds) start flashing. The flashes are counting out 2-digit trouble codes. Fast flashes count up each digit, with a longer pause between digits. On TJ’s with a digital odometer, the code numbers are printed on the odometer in addition to flashing the check engine light. 55 indicates the end of all codes. Once you’ve got your code list, consult the table below to see what they mean.
OBD-II information is more complex, so the codes for 1998 and newer Jeeps can’t be displayed by flashing the check engine light. However, those vehicles which have digital odometers will display the codes on the odometer. I’ve verified this personally on a 1999 WJ. For those vehicles without digital odometers, or for anybody who wants an English description rather than just a numeric code, an OBD-II code scanner ($20-300) can be plugged in under the dash. OBD-II codes can be looked up online here.
These codes were taken from the ’95 XJ/YJ factory service manual, and probably apply to most other OBD-I-era Jeeps.
| Code | Description |
|---|---|
| 11* | No crank reference signal detected during engine cranking. |
| 12* | Direct battery input to PCM was disconnected within the last 50 key-on cycles. |
| 13** | No difference recognized between the engine MAP reading and the barometric (atmospheric) pressure reading at start-up |
| 14** | MAP sensor input below minimum acceptable voltage. or MAP sensor input above maximum acceptable voltage. |
| 15** | No vehicle distance (speed) sensor signal detected during road load conditions. |
| 17* | Engine coolant temperature remains below normal operating temperatures during vehicle travel (thermostat). |
| 21** | Neither rich nor lean condition detected from the oxygen sensor input. or Oxygen sensor input voltage maintained above the normal operating range. |
| 22** | Engine coolant temperature sensor input above maximum acceptable voltage. or Engine coolant temperature sensor input below minimum acceptable voltage. |
| 23** | Intake manifold air temperature sensor input above maximum acceptable voltage. or Intake manifold air temperature sensor input below minimum acceptable voltage. |
| 24** | Throttle position sensor input above maximum acceptable voltage. or Throttle position sensor input below minimum acceptable voltage. |
| 25** | A shorted condition detected in one or more of the idle air control motor circuits. |
| 27* | Injector #1 output driver does not respond properly to the control signal. or Injector #2 output driver does not respond properly to the control signal. or Injector #3 output driver does not respond properly to the control signal. or Injector #4 output driver does not respond properly to the control signal. or Injector #5 output driver does not respond properly to the control signal. or Injector #6 output driver does not respond properly to the control signal. |
| 33* | An open or shorted condition detected in the A/C clutch relay circuit. |
| 34* | An open or shorted condition detected in the speed control vacuum or vent solenoid circuits. or Speed control switch input below the minimum acceptable voltage. or Speed control switch input above the maximum acceptable voltage. |
| 35* | An open or shorted condition detected in the radiator fan relay circuit. |
| 41* | An open or shorted condition detected in the generator field control circuit. |
| 42* | An open or shorted condition detected in the auto shutdown relay circuit. |
| 44* | 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** | Battery voltage sense input above target charging voltage during engine operation. |
| 47** | Battery voltage sense input below target charging voltage during engine operation. Also, no significant change detected in battery voltage during active test of generator output. |
| 51** | Oxygen sensor signal input indicates lean air/fuel ratio condition during engine operation. |
| 52** | Oxygen sensor signal input indicates rich air/fuel ratio condition during engine operation. |
| 53* | PCM internal fault condition detected. |
| 54* | No fuel sync (camshaft signal) detected during engine cranking. |
| 55* | Completion of diagnostic trouble code display on the malfunction indicator lamp (check engine lamp). |
| 62* | Unsuccessful attempt to update SRI (service reminder indicator) miles in the PCM EEPROM. |
| 63* | Unsuccessful attempt to write to an EEPROM location by the PCM. |
* – Check engine lamp will not illuminate at all times if this code was recorded. Cycle ignition key as described and observe code flashed by check engine lamp.
** – Check engine lamp will illuminate during engine operation if this code was recorded.
PCM = Powertrain Control Module (the engine computer)
MAP = Manifold Absolute Pressure (the sensor that measures how hard the engine is sucking air through the intake manifold
EEPROM = Electrically Erasable Programmable Read Only Memory (a type of computer chip used inside the PCM)
[Last updated 1 Sep 2008]
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I HAVE A JEEP YJ 94 WITH 2.5 CHECK CODE WITH KEY ON /OFF 3 TIMES 76 IS CODE WHAT DOES MEAN
Interesting. The ’95 factory service manual doesn’t list 76 as a possible code. However, google tells me that you’re not the first person to encounter this:
https://www.jeepforum.com/forum/f12/trouble-code-76-a-1443074/
Generically, 76 indicates an open or short in the fuel pump relay ballast resistor. However, a ’94 YJ doesn’t have a ballast resistor, so it shouldn’t ever throw that code. Does your Jeep still have the original engine, or was it replaced somewhere along the way with an older or rebuilt engine? That might explain why you’re getting that code.
If you do have a ballast resistor, it’ll be located in the engine bay by the brake master cylinder. It’s a white ceramic box roughly 3/4 x 3″ in size with one wire sticking out each end. Here’s a video that shows how to test & replace it:
https://www.youtube.com/watch?v=0M9piFUSDwo
Hi! Help!
94 jeep cherokee 2.5 manual transmission. What the heck does code 3-5-5 mean?
I got 3 codes! Ran it 3 times same thing.!¿
Hey Julie,
All of the trouble codes are two digits. The final two digits, 55, indicate that you’ve reached the end of the list and there are no more codes. You state that the first digit is 3, but I suspect that it’s really either 12 (meaning you disconnected the battery recently) or 21 (meaning there’s an oxygen sensor problem).
What sort of problem are you trying to track down?
Hi
Any help with the following, greatly appreciated
93 YJ 4
Hey Roger, what exactly do you need help with?
Hi any help with the following problem appreciated.
93 YJ 4.0 tried connecting aftermarket OBD1 connector with nil response
Problem;- vehicle starts & runs fine until driving slowly in traffic, starts missing, loosing power erratictically before stalling then fails to restart for approx. 20 mins. Will then restart until the next drive in slow moving traffic.
Replaced the distributor, coil, plugs, leads, crank sensor all to no avail.
Engine runs fine on the open road
Any help desperately needed
Hmm… Does your check engine light come on? If so, what does the key sequence described above tell you?
You’ve already replaced your ignition system, which was my first guess.
It must be something heat related, since it fails when you slow down and then won’t start until the engine cools off. Does your temp gauge ever get above 210F?
It sounds like vapor lock, but I’ve never seen that on a fuel injected 4.0L. Carbureted engines suffer from that a lot, especially in hot weather. The fix is to keep your fuel lines as far as possible from your exhaust, and to keep your engine bay as cool as possible.
Can you put a fuel pressure gauge on the fuel rail and see what it says? I wonder if your fuel pump isn’t putting out enough pressure.
How old is your fuel filter? I think I’ve had to replace mine 2 or 3 times in 120K miles. However, I would expect that to have more trouble at high RPM, not at low RPM.
Do you have any exhaust leaks around your manifold that are heating up the engine bay or fuel lines beyond where they should be?
Hi Thanks for the prompt reply,
Fuel filter replaced yesterday, engine temp remains steady all the time, no exhaust or manifold leaks, our temperature never exceeds 90f.
The engine codes we got from the light
were 12,21,22,24,54
Hence we thought crank sensor but the voltage from the old one said it was fine
We replaced it anyway to be sure
Problem still remains
It’s complaining about several different sensors all having issues at the same time. The odds of all of those sensors all dying at the same time is near zero. It sounds like you’ve got a damaged wiring harness somewhere that’s preventing them all from talking to the engine computer.
The easiest thing to try is to disconnect, clean, and reconnect each of those connectors. If that helps, great. If not, you’ll need to trace the wires back to the computer and look for anything damaged, loose, or disconnected.