Is Your 1994 Jeep Wrangler OBD2 Compliant? Decoding and Diagnosing Engine Issues

For owners of the rugged and classic 1994 Jeep Wrangler, understanding your vehicle’s diagnostic systems is key to maintaining its performance and longevity. As automotive technology evolved in the mid-1990s, On-Board Diagnostics (OBD) systems became increasingly sophisticated. A crucial question for 1994 Wrangler owners often arises: Is my Jeep equipped with the older OBDI system, or does it feature the more advanced OBD2? Knowing the answer is the first step in effectively diagnosing and addressing any “check engine” light issues.

This guide will walk you through understanding the diagnostic systems in your 1994 Jeep Wrangler, how to retrieve trouble codes – often referred to as fault codes or error codes – and what these codes mean. While this information serves as a valuable starting point for troubleshooting, always remember that it’s not a substitute for professional diagnostic tools and expertise.

Decoding Diagnostic Systems: OBDI vs. OBD2 for the ’94 Wrangler

The 1994 model year is an interesting period in automotive diagnostics. It sits on the cusp of the transition from the first generation On-Board Diagnostics (OBD) to the now-standard OBD2 system. Generally, vehicles from this era, including the 1994 Jeep Wrangler, are typically equipped with OBDI systems.

OBD systems were designed to monitor various engine and emission control components. When a problem is detected, the system illuminates the “check engine” light (or malfunction indicator lamp – MIL) and stores a diagnostic trouble code (DTC) in the vehicle’s computer. These codes offer clues about the nature of the problem, helping mechanics and DIY enthusiasts pinpoint the source of the issue.

While OBD served its purpose, it was not standardized across manufacturers. This lack of uniformity led to the development of OBD2, which offered significant improvements:

• Standardized Codes: OBD2 uses a universal set of diagnostic trouble codes, making it easier to understand issues across different makes and models.
• Enhanced Diagnostics: OBD2 systems monitor a broader range of parameters and provide more detailed information.
• Standardized Connector: OBD2 utilizes a standard 16-pin Diagnostic Link Connector (DLC), simplifying the connection of scan tools.

For your 1994 Jeep Wrangler, understanding that it likely uses an OBDI system is crucial. This means the code retrieval process and the interpretation of codes will differ from OBD2 vehicles. However, some late 1994 models or those manufactured for California emissions standards might have early OBD2 implementations. Therefore, knowing how to check for both systems is beneficial.

Retrieving Diagnostic Trouble Codes from Your 1994 Jeep Wrangler

Regardless of whether your 1994 Wrangler is equipped with OBDI or a very early version of OBDII, you can retrieve diagnostic codes without a scan tool using a simple method known as the “key trick.” This procedure utilizes the vehicle’s check engine light (for OBDI) or the digital odometer (for some early OBDII implementations) to communicate the stored trouble codes.

Here’s how to perform the “key trick” for your 1994 Jeep Wrangler, covering both potential scenarios:

The “Key Trick” for OBDI Jeep Wranglers (Likely for 1994 Models)

This method uses the check engine light to flash out the diagnostic codes.

1. Start with the ignition OFF. Ensure the key is not in the ignition or turned to any position.
2. Perform the key cycle: Within five seconds, cycle the ignition key from OFF to ON and back to OFF, repeating this sequence three times, ending in the ON position. The sequence is: ON – OFF – ON – OFF – ON. (Remember, “ON” is the position just before “START,” and “OFF” is not “LOCK”).
3. Observe the “Check Engine” light: The “check engine” light will begin to flash. Count the flashes to decipher the two-digit trouble codes.
4. Decoding the flashes: Each code is represented by a two-digit sequence. For example, code 23 would be indicated by: FLASH FLASH (pause) FLASH FLASH FLASH (long pause). The “pause” separates the digits of a code, and the “long pause” separates individual codes.
5. End of codes: The code 55 indicates “End of Codes” and is a normal signal, signifying that the system has finished displaying all stored trouble codes. It’s not an error code itself.

Important Notes for OBDI Key Trick:

• Parking Brake: In some cases, you may need to set the parking brake for the codes to display correctly.
• Blink Spacing: Older systems might have slightly uneven blink spacing. If you see a sequence like “23 23,” it is likely just a single “55” (End of Codes). Codes are not typically repeated.

Checking for Odometer Display (Potentially for very early OBDII or specific models)

Some newer models of this era with digital odometers might display codes directly on the odometer. While less likely for a 1994 Wrangler, it’s worth checking:

1. Insert the key and press the odometer reset button. Keep the reset button pressed down.
2. Turn the key to the RUN position (while still holding the odometer reset button).
3. Release the odometer reset button.
4. Observe the odometer: The odometer will go through a sequence of numbers (e.g., 111111 to 999999), then may display the vehicle’s serial number. Following this, it might show error codes, often starting with a “P” (for Powertrain codes, which are standard OBD2 codes).
5. If this method doesn’t work: It’s highly probable your 1994 Wrangler utilizes the OBDI “key trick” method described above.

OBDI Computer Codes for 1994 Jeep Wrangler (and Similar Models)

Once you have retrieved the codes using the OBDI “key trick,” you’ll need to interpret them. Below is a comprehensive list of OBDI codes that may be relevant to your 1994 Jeep Wrangler and similar Chrysler vehicles of that era. Remember that these codes are aids for troubleshooting, not definitive repair instructions. Always consult a repair manual or qualified mechanic for diagnosis and repair verification.

Important Disclaimer: This code list is compiled from various sources and may not be exhaustive or perfectly accurate for every 1994 Jeep Wrangler configuration. Codes can sometimes indicate a problem that is indirectly related to the actual faulty component. Always verify diagnoses with further testing and professional guidance.

OBDI Trouble Codes:

• 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. (This code often appears after battery service and may not indicate a current problem if the vehicle is running normally).
• 13 – MAP sensor or vacuum line may not be working. (Manifold Absolute Pressure sensor – crucial for engine load and fuel mixture calculations).
• 14 – MAP sensor voltage below .16V or over 4.96V. (Indicates an electrical issue with the MAP sensor circuit).
• 15 – No speed/distance sensor signal. (Vehicle Speed Sensor – affects speedometer, cruise control, and potentially transmission operation).
• 16 – Loss of battery voltage detected with engine running. (Charging system issue or voltage drop problem).
• 17 – Engine stays cool too long (bad thermostat or coolant sensor?) OR (1985 turbo only): knock sensor circuit. (Relates to engine temperature regulation – thermostat or coolant temperature sensor issues).
• 21 – Oxygen sensor signal doesn’t change (stays at 4.3-4.5V). Probably bad oxygen sensor. (Oxygen sensor is vital for monitoring exhaust gases and adjusting fuel mixture).
• 22 – Coolant sensor signal out of range – May have been disconnected to set timing. (Coolant Temperature Sensor – important for engine temperature readings and fuel control).
• 23 – Incoming air temperature sensor may be bad. (Intake Air Temperature sensor – measures the temperature of air entering the engine).
• 24 – Throttle position sensor over 4.96V. (Throttle Position Sensor – indicates throttle valve angle to the computer).
• 25 – Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached. (Automatic Idle Speed motor – controls idle speed).
• 26 – Peak injector circuit voltage has not been reached (need to check computer signals, voltage reg, injectors). (Injector circuit issue – could be wiring, voltage regulator, or injectors themselves).
• 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. (Injector circuit malfunction – check wiring, connectors, and potentially the ECU).
• 31 – Bad evaporator purge solenoid circuit or driver. (Evaporative Emission Control system – related to fuel vapor management).
• 32 – (1984 only) power loss/limited lamp or circuit OR 32 EGR gases not working (1988) – check vacuum, valve OR 32 (1990-92) computer didn’t see change in air/’fuel ratio when EGR activated – check valve, vacuum lines, and EGR electrical. (Exhaust Gas Recirculation system – reduces NOx emissions).
• 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). (Air Conditioning Clutch Relay – related to the A/C system operation).
• 34 – (1984-86) EGR solenoid circuit shorted or open OR 34 (1987-1991) speed control shorted or open. (EGR solenoid or Speed Control – depending on the specific year and system).
• 35 – Cooling fan relay circuit open or shorted OR 35 idle switch motor fault – check connections. (Cooling Fan Relay – controls the engine cooling fan; Idle Switch Motor – related to idle control).
• 36 – (turbo only) Wastegate control circuit open or shorted. (Turbo Wastegate Control – specific to turbocharged engines, not typically found in standard 1994 Wranglers).
• 37 – Shift indicator light failure, 5-speed OR part throttle lock/unlock solenoid driver circuit (87-89) OR solenoid coil circuit (85-87 Turbo only) OR Trans temperature sensor voltage low (1995 and on). (Transmission related issue – depending on the specific transmission and year).
• 41 – Alternator field control circuit open or shorted. (Alternator Field Control – charging system regulation).
• 42 – Automatic shutdown relay circuit open or shorted OR 42 Fuel pump relay control circuit OR 42 Fuel level unit – no change over miles OR 42 Z1 voltage missing when autoshutdown circuit energized. (Automatic Shutdown Relay – critical for engine operation and fuel delivery; Fuel Pump Relay – controls fuel pump; Fuel Level Unit – fuel gauge system).
• 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. (Ignition coil issue; Cylinder Misfire – engine combustion problem; Power Module/Logic Module communication issue).
• 44 – No FJ2 voltage present at logic board OR 44 Logic module self-diagnostics indicate problem OR 44 Battery temperature out of range. (Logic Module – engine computer problem; Battery Temperature – battery temperature sensor issue).
• 45 – Turbo boost limit exceeded (engine was shut down by logic module). (Turbo Boost Limit – turbocharger system issue, not typical for standard 1994 Wranglers).
• 46 – Battery voltage too high during charging or charging system voltage too low. (Charging System Voltage – overcharging or undercharging issue).
• 47 – Battery voltage too low and alternator output too low. (Low Battery Voltage and Alternator Output – charging system malfunction).
• 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. OR 51 Internal logic module fault (’84 turbo only). (Oxygen sensor lean – potential fuel mixture or sensor issue; Logic Module Fault – engine computer problem, less likely in 1994 models).
• 52 – Oxygen sensor stuck at rich position OR 52 Internal logic module fault (’84 turbo only). (Oxygen sensor rich – potential fuel mixture or sensor issue; Logic Module Fault – engine computer problem, less likely in 1994 models).
• 53 – Logic module internal problem. (Logic Module Fault – engine computer issue).
• 54 – No sync pickup signal during engine rotation (turbo only) OR 54 Internal logic module fault (’84 turbo only) – or camshaft sensor/distributor timing. (Sync Pickup Signal – crankshaft/camshaft sensor issue; Logic Module Fault – engine computer problem; Distributor Timing – ignition timing problem).
• 55 – End of codes. (Normal indication – not an error).
• 61 – “Baro” sensor open or shorted. (Barometric Pressure Sensor – measures atmospheric pressure).
• 62 – EMR mileage cannot be stored in EEPROM OR PCM failure SRI mile not stored. (EEPROM/PCM issue – related to odometer or computer memory).
• 63 – Controller cannot write to EEPROM. (EEPROM issue – computer memory problem).
• 64 – Catalytic converter efficiency failure. (Catalytic Converter Efficiency – emissions system problem).
• 65 – Power steering switch failure. (Power Steering Switch – related to power steering system, may affect idle speed).
• 66 – No CCD Message From TCM and/or No CCD Message From BCM. (CCD Communication – communication issue between computer modules – Transmission Control Module (TCM) and Body Control Module (BCM)).

Moving Beyond the Codes: Diagnosis and Repair

Retrieving and decoding trouble codes for your 1994 Jeep Wrangler is a significant first step in diagnosing engine or emission-related problems. However, remember these key points:

• Codes are starting points: A trouble code indicates a potential problem area, not necessarily the exact failed component. Further investigation is always required.
• Use code readers for enhanced information: While the “key trick” is helpful, modern OBDII code readers (even if your ’94 is OBDI, some readers can interface with older systems) provide more detailed information, including live data streams from sensors. This can greatly aid in pinpointing intermittent issues or confirming sensor readings.
• Consult a repair manual: A repair manual specific to your 1994 Jeep Wrangler is an invaluable resource. It will provide detailed troubleshooting steps, wiring diagrams, and component locations.
• Seek professional help when needed: If you are uncomfortable with automotive diagnostics or repair, or if the problem is complex, don’t hesitate to consult a qualified mechanic. They have specialized tools and expertise to accurately diagnose and repair your vehicle.

By understanding the diagnostic capabilities of your 1994 Jeep Wrangler and learning how to interpret trouble codes, you can take a proactive approach to vehicle maintenance and ensure your classic Wrangler continues to perform reliably for years to come.