Decoding Your 1993 YJ Jeep’s Check Engine Light: Understanding the OBDI System

For owners of the classic 1993 Jeep Wrangler YJ, understanding your vehicle’s diagnostic system is crucial for maintenance and troubleshooting. You might be wondering, “Does my 93 YJ Jeep have OBD2?” The answer is no. The 1993 Jeep Wrangler YJ, like other vehicles of its era, utilizes an OBD1 (On-Board Diagnostics 1) system, not the more modern OBD2. This is a key distinction, as the diagnostic procedures and error codes are different.

This guide will walk you through everything you need to know about accessing and interpreting diagnostic codes on your 1993 YJ Jeep. While it’s not OBD2, the OBDI system still provides valuable insights into your Jeep’s health, helping you identify potential issues and keep your ride running smoothly.

Understanding OBDI in Your 1993 Jeep Wrangler YJ

Before OBD2 became the standard in 1996, manufacturers used various proprietary OBDI systems. Chrysler, the maker of Jeep, had its own version. Unlike OBD2, which uses a standardized connector and a universal set of codes, OBDI systems are specific to the manufacturer and often the model year.

For your 1993 YJ Jeep, this means you won’t find the familiar OBD2 port under the dashboard. Instead, accessing diagnostic information requires a different approach, often referred to as the “key trick.” It’s important to note that while OBDI is less sophisticated than OBD2, it still serves the purpose of alerting you to potential problems detected by the vehicle’s computer (ECU – Engine Control Unit).

What to Expect from the OBDI System

• Basic Diagnostics: OBDI primarily focuses on emission-related issues but also covers other engine and sensor malfunctions.
• Limited Data: Compared to OBD2, OBDI provides less data and fewer parameters.
• Code Retrieval Method: You’ll use the “key trick” method described below to retrieve codes, not a standard OBD2 scanner.
• Two-Digit Codes: OBDI codes for your 1993 YJ are typically two-digit numbers.

Retrieving OBDI Codes on a 1993 YJ Jeep: The “Key Trick”

The “key trick” is a simple yet effective way to get your 1993 YJ Jeep to display its diagnostic trouble codes. Here’s how to do it:

1. Start with the ignition OFF. Make sure your key is out of the ignition or in the “Lock” position.
2. Perform the Key Cycle: Within five seconds, rapidly switch the ignition key from “OFF” to “ON” and back to “OFF” 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: After the final “ON” position, the “Check Engine” light on your dashboard will begin to flash.
4. Count the Flashes: Carefully count the flashes. The codes are two-digit numbers. For example, code 23 would be represented as: FLASH FLASH (pause) FLASH FLASH FLASH (long pause). A “long pause” separates the two digits of a code, and an even longer pause separates different codes if multiple codes are stored.
5. Code 55: End of Codes: The sequence will end with code 55, indicated by FLASH FLASH FLASH FLASH FLASH (long pause). This is normal and simply signifies the end of the diagnostic code output.

Important Notes for Code Retrieval:

• Parking Brake: Some sources suggest setting the parking brake might be necessary for the codes to display. It’s a good practice to engage the parking brake before starting the procedure.
• Flash Spacing: On older models like the 1993 YJ, the timing of the flashes might not be perfectly uniform. Be patient and focus on counting the flashes and recognizing the pauses.
• No Code Repetition: Codes are not repeated. If you see a sequence that seems to repeat (like 23 23), it’s likely just a single code 55, indicating no fault codes are stored.

1993 Jeep Wrangler YJ OBDI Computer Codes: A Comprehensive List

Once you’ve retrieved the codes using the key trick, you’ll need to interpret them. Below is a detailed list of OBDI codes relevant to older Chrysler vehicles, including your 1993 Jeep YJ. Remember, while this list is comprehensive, it’s essential to use it as a troubleshooting aid, not a definitive repair manual. Always consult a qualified mechanic for diagnosis and repairs.

OBDI Codes for 1993 Jeep Wrangler YJ

• 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 routine maintenance or battery replacement and may not indicate a problem if the Jeep is running normally.
• 13: MAP sensor or vacuum line may not be working. Check the Manifold Absolute Pressure (MAP) sensor and its vacuum lines for leaks or damage.
• 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. Relates to the Vehicle Speed Sensor (VSS).
• 16: Loss of battery voltage detected with engine running. Points to charging system issues.
• 17: Engine stays cool too long (bad thermostat or coolant sensor?). Indicates a potential issue with the thermostat or coolant temperature sensor affecting engine warm-up.
• 21: Oxygen sensor signal doesn’t change (stays at 4.3-4.5V). Probably bad oxygen sensor. Suggests a faulty oxygen sensor.
• 22: Coolant sensor signal out of range. May have been disconnected to set timing. Could be a disconnected or malfunctioning coolant temperature sensor.
• 23: Incoming air temperature sensor may be bad. Indicates a problem with the Intake Air Temperature (IAT) sensor.
• 24: Throttle position sensor over 4.96V. High voltage reading from the Throttle Position Sensor (TPS).
• 25: Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached. Issues with the Automatic Idle Speed motor, which controls idle speed.
• 26: Peak injector circuit voltage has not been reached. (need to check computer signals, voltage reg, injectors). Potential problem in the fuel injector circuit.
• 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. Indicates an issue with injector control.
• 31: Bad evaporator purge solenoid circuit or driver. Problem in the evaporative emission control system, specifically the purge solenoid.
• 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. Issues with the Exhaust Gas Recirculation (EGR) system.
• 33: Air conditioning clutch relay circuit open or shorted. Relates to the air conditioning system’s clutch relay.
• 34: (1984-86) EGR solenoid circuit shorted or open OR 34 (1987-1991) speed control shorted or open. Could be EGR solenoid or speed control issue depending on the specific model year.
• 35: Cooling fan relay circuit open or shorted OR 35 idle switch motor fault – check connections. Problems with the cooling fan relay or idle switch motor.
• 36: (turbo only) Wastegate control circuit open or shorted. Relevant only for turbocharged models (unlikely on a 1993 YJ).
• 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, could be shift indicator or solenoid circuit.
• 41: Alternator field control circuit open or shorted. Indicates a fault in the alternator control circuit.
• 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. Multiple possibilities related to the automatic shutdown relay, fuel pump relay, or fuel level sensor.
• 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 or cylinder misfire.
• 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 or battery temperature sensor issue.
• 45: Turbo boost limit exceeded (engine was shut down by logic module). Turbo-related, not applicable to most 1993 YJs.
• 46: Battery voltage too high during charging or charging system voltage too low. Charging system voltage problem.
• 47: Battery voltage too low and alternator output too low. Low battery voltage and alternator output issues.
• 51: Oxygen sensor stuck at lean position. OR 51 Internal logic module fault (’84 turbo only). Oxygen sensor or potentially logic module fault.
• 52: Oxygen sensor stuck at rich position OR 52 Internal logic module fault (’84 turbo only). Oxygen sensor or logic module fault.
• 53: Logic module internal problem. Internal computer (logic module) problem.
• 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 signal or logic module issue, or camshaft/distributor timing problem.
• 55: End of codes. Normal, indicates the end of the diagnostic code display.
• 61: “Baro” sensor open or shorted. Barometric pressure sensor issue.
• 62: EMR mileage cannot be stored in EEPROM OR PCM failure SRI mile not stored. Related to mileage storage in computer memory.
• 63: Controller cannot write to EEPROM. Computer memory write error.
• 64: Catalytic converter efficiency failure. Catalytic converter performance issue.
• 65: Power steering switch failure. Power steering pressure switch problem.
• 66: No CCD Message From TCM and/or No CCD Message From BCM. Communication issue with Transmission Control Module (TCM) or Body Control Module (BCM).

Disclaimer: This code list is for informational purposes and should be used as a starting point for diagnosis. Accuracy is not guaranteed, and codes can sometimes be misleading. Always consult a qualified mechanic for proper diagnosis and repair of your 1993 Jeep Wrangler YJ.

Beyond the Key Trick: Considering Professional Diagnostics

While the key trick is a valuable tool for 1993 YJ Jeep owners, it’s important to understand its limitations. OBDI systems are less sophisticated than OBD2, and the “key trick” method provides only basic error codes.

For more in-depth diagnostics, consider:

• OBDI Scan Tools: While not as common as OBD2 scanners, there are still OBDI scan tools available that can provide more detailed information than the key trick. These tools may be able to read live data and perform some diagnostic tests.
• Professional Mechanic: A qualified mechanic with experience in older vehicles will have specialized tools and knowledge to diagnose complex issues on your 1993 YJ Jeep. They can go beyond basic code reading and perform thorough inspections and tests to pinpoint the root cause of any problem.

Conclusion: Leveraging OBDI for Your 1993 YJ Jeep

While your 1993 Jeep Wrangler YJ doesn’t have OBD2, its OBDI system is still a useful diagnostic tool. By understanding the “key trick” and the associated error codes, you can gain valuable insights into your vehicle’s condition and address potential issues proactively.

Remember to use the code list as a guide and prioritize professional diagnosis for accurate troubleshooting and repair. Keeping your classic 1993 YJ Jeep running its best requires understanding its unique systems, and the OBDI system is a key part of that knowledge.