Decoding Your 1994 Jeep Wrangler OBD Codes: A Comprehensive Guide

Understanding the diagnostic codes of your 1994 Jeep Wrangler is crucial for maintaining its performance and addressing any potential issues. While the term “OBD2” is commonly searched, it’s important to clarify that the 1994 Wrangler utilizes an OBDI system. This guide will walk you through the process of retrieving and interpreting these OBDI codes, empowering you to troubleshoot your vehicle effectively.

Understanding OBD and Your 1994 Wrangler

The On-Board Diagnostics (OBD) system is essentially your vehicle’s self-monitoring system. It tracks the performance of various engine and emission components, alerting you to potential problems through the “Check Engine” light. For 1994 Jeep Wranglers, this system is OBDI, the precursor to the more standardized OBDII systems found in later models (generally post-1996).

It’s common for owners of ’94 Wranglers to search for “94 Wrangler Obd2” because OBDII is more widely known and used today. However, to accurately diagnose your 1994 model, you need to understand and utilize the OBDI system it’s equipped with. This system, while less sophisticated than OBDII, still provides valuable diagnostic information through a series of fault codes.

Retrieving OBDI Trouble Codes on a 1994 Jeep Wrangler: The “Key Trick”

Unlike OBDII systems that require a scan tool to read codes, the 1994 Jeep Wrangler’s OBDI system allows you to retrieve codes using a simple “key trick”. This method involves turning the ignition key in a specific sequence to make the “Check Engine” light flash out the diagnostic codes.

Here’s how to perform the “key trick” on your 1994 Jeep Wrangler:

Start with the ignition OFF. Make sure your key is out of the ignition or turned to the “Lock” position.
Perform the key cycle: Within five seconds, switch the ignition key from OFF to ON, then OFF, then ON, then OFF, and finally ON again. Remember, “ON” is the position just before starting the engine, and “OFF” is not “Lock”. The sequence is: ON-OFF-ON-OFF-ON.
Observe the “Check Engine” light: After completing the key cycle, the “Check Engine” light will begin to flash. Carefully count the flashes.

Alt text: Close-up of the dashboard of a 1994 Jeep Wrangler highlighting the illuminated Check Engine light.

Interpreting the OBDI Flashing Codes

The OBDI codes are communicated through a series of flashes from the “Check Engine” light. These are two-digit codes. Here’s how to interpret them:

Counting Flashes: Count the flashes of the “Check Engine” light. A code like “23” will be represented as: FLASH FLASH (pause) FLASH FLASH FLASH (longer pause). The pauses are crucial for separating the digits and individual codes.
Two-Digit Codes: Each code is composed of two digits. The flashes are grouped to represent each digit.
Code 55: End of Codes: After all diagnostic codes have been displayed, you will see code “55,” which signifies the “End of Codes.” This is a normal indication that the system has finished displaying all stored codes. If you see a sequence like 23 23, it’s likely just a single code 55 due to spacing variations in older systems. Codes are not typically repeated.

It’s important to note that the blink spacing on older OBDI systems might not be perfectly uniform. Pay close attention to the pauses to correctly distinguish between digits and separate codes.

1994 Jeep Wrangler (OBDI) Trouble Codes

Below is a comprehensive list of OBDI trouble codes that may be displayed by your 1994 Jeep Wrangler. This list is compiled to be as accurate as possible but should be used as a troubleshooting aid, not a definitive repair manual. Always consult a qualified mechanic for diagnosis and repair verification.

Important Note: Some codes may be relevant to Chrysler vehicles in general and not specifically to Jeep Wranglers.

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 is often normal if you’ve recently disconnected your battery.
13 – MAP sensor or vacuum line may not be working. Check vacuum lines to the Manifold Absolute Pressure (MAP) sensor for leaks or disconnections.
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. Problem with the Vehicle Speed Sensor (VSS) or its circuit.
16 – Loss of battery voltage detected with engine running. Could indicate charging system issues.
17 – Engine stays cool too long (bad thermostat or coolant sensor?). Suggests a problem with the thermostat or Engine Coolant Temperature (ECT) sensor.
21 – Oxygen sensor signal doesn’t change (stays at 4.3-4.5V). Probably bad oxygen sensor. Likely indicates a faulty oxygen sensor.
22 – Coolant sensor signal out of range. May have been disconnected to set timing. Check the ECT sensor and its wiring.
23 – Incoming air temperature sensor may be bad. 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. Issue with the idle control system.
26 – Peak injector circuit voltage has not been reached. (need to check computer signals, voltage reg, injectors). Potential injector circuit problem.
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 or driver issue.
31 – Bad evaporator purge solenoid circuit or driver. Problem with the evaporative emissions purge system.
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 (EGR) system malfunction.
33 – Air conditioning clutch relay circuit open or shorted. A/C clutch relay circuit issue. May be normal on models without A/C.
34 – (1984-86) EGR solenoid circuit shorted or open OR 34 (1987-1991) speed control shorted or open. EGR or speed control issue depending on the year (though ’94 is beyond these years, this code might still be relevant).
35 – Cooling fan relay circuit open or shorted OR 35 idle switch motor fault – check connections. Cooling fan or idle switch circuit problem.
36 – (turbo only) Wastegate control circuit open or shorted. (Not applicable to standard 1994 Wrangler engines).
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). Potentially related to transmission or shift indicator (though some parts may not be relevant to ’94 Wrangler).
41 – Alternator field control circuit open or shorted. Charging system or alternator field control circuit issue.
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, fuel pump relay, or fuel level sensor issue.
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, cylinder misfire, or computer communication problem.
44 – No FJ2 voltage present at logic board OR 44 Logic module self-diagnostics indicate problem OR 44 Battery temperature out of range. Computer logic module or battery temperature sensor issue.
45 – Turbo boost limit exceeded (engine was shut down by logic module). (Not applicable to standard 1994 Wrangler engines).
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 charging system output.
51 – Oxygen sensor stuck at lean position. May be tripped by a bad MAP sensor system causing a rich condition. OR 51 Internal logic module fault (’84 turbo only). Oxygen sensor or MAP sensor issue.
52 – Oxygen sensor stuck at rich position OR 52 Internal logic module fault (’84 turbo only). Oxygen sensor or computer logic module issue.
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. (Potentially camshaft sensor or distributor timing issue for ’94 Wrangler, ignore “turbo only”).
55 – End of codes. Normal indication, not a fault.
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. EEPROM or PCM (Powertrain Control Module) issue related to mileage storage (less relevant for typical DIY troubleshooting).
63 – Controller cannot write to EEPROM. Controller issue related to EEPROM writing (less relevant for typical DIY troubleshooting).
64 – Catalytic converter efficiency failure. Catalytic converter efficiency problem.
65 – Power steering switch failure. Power steering pressure switch issue.
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) – may be less applicable to the ’94 Wrangler’s simpler systems.

Alt text: Diagram showing the location of the OBDI diagnostic connector in a 1994 Jeep Wrangler, typically under the dashboard on the driver’s side.

What About OBD2 and the ’94 Wrangler?

As mentioned earlier, the 1994 Jeep Wrangler is equipped with an OBDI system, not OBD2. OBD2 became standard in the USA in 1996. Therefore, directly searching for “94 wrangler obd2 codes” or expecting OBD2 functionality on this model year will lead to confusion.

While there might be some overlap in certain generic diagnostic concepts between OBDI and OBD2, the code lists and retrieval methods are distinctly different. For a 1994 Wrangler, you must use the OBDI “key trick” and refer to OBDI code charts for accurate diagnosis.

Beyond Code Reading: Effective Diagnostics

Retrieving OBDI codes is just the first step in diagnosing your 1994 Jeep Wrangler. Here’s what to do after you have your codes:

Record the Codes: Write down all the codes you retrieve in the order they appear.
Consult a Repair Manual: A repair manual specific to the 1994 Jeep Wrangler will provide more detailed information about each code, potential causes, and troubleshooting steps.
Visual Inspection: Before replacing any parts, perform a thorough visual inspection of the affected system. Check for:
- Vacuum leaks: Especially for MAP sensor related codes (13, 14).
- Wiring issues: Check for damaged, loose, or corroded wires and connectors.
- Fluid leaks: If the code relates to a sensor in a fluid system.
Component Testing (if possible): Depending on your mechanical skills and tools, you might be able to test sensors or components directly (e.g., using a multimeter).
Seek Professional Help: If you’re unsure about the diagnosis or repair process, or if the problem persists after your initial troubleshooting, it’s always best to consult a qualified mechanic. They have specialized tools and expertise to accurately diagnose and repair your 1994 Jeep Wrangler.

Conclusion

Understanding and utilizing the OBDI system on your 1994 Jeep Wrangler is essential for effective vehicle maintenance. By using the “key trick” and this code list, you can gain valuable insights into potential issues. Remember that this guide is for informational purposes and should be used in conjunction with proper repair procedures and, when needed, professional assistance. Keeping your ’94 Wrangler running smoothly involves understanding its systems, and diagnostics are a key part of that process.