Decoding Jeep OBD2 Codes: A Comprehensive Guide to Check Engine Lights

Navigating car troubles can be stressful, especially when that check engine light illuminates on your Jeep’s dashboard. Fortunately, modern Jeeps, like most vehicles, are equipped with an On-Board Diagnostics system, specifically OBD-II, which can help pinpoint potential issues. This guide will help you understand Jeep Obd2 Codes, how to retrieve them, and what they might mean, empowering you to troubleshoot common problems and seek appropriate solutions.

Understanding OBD-I and OBD-II Systems in Jeeps

Jeep vehicles, depending on their year of manufacture, may utilize either an older OBD-I system or the more standardized OBD-II system. OBD-I systems were less uniform and manufacturer-specific, while OBD-II, standardized in the mid-1990s, offers a more consistent diagnostic approach across different makes and models.

For Jeep owners, understanding which system your vehicle uses is the first step. Generally, Jeeps manufactured from 1996 onwards are OBD-II compliant. While this guide primarily focuses on OBD-II codes, we will also touch upon retrieving OBD-I codes for older models.

How to Retrieve Jeep OBD Codes Using the Key Trick

One of the convenient aspects of many Jeep models is the “key trick” method for retrieving diagnostic trouble codes without needing a dedicated OBD-II scanner. This method utilizes the ignition key to prompt the vehicle’s computer to display stored codes. Here’s how to perform the key trick for both older (OBD-I) and newer (OBD-II) Jeeps:

For Older Jeep Models (OBD-I):

Turn the Ignition Off: Ensure your Jeep’s ignition is completely off.
Key Cycling: Within five seconds, quickly cycle the ignition key between the “On” and “Off” positions three times, ending in the “On” position. Remember, “On” is not starting the engine, and “Off” is not the “Lock” position. The sequence is: On – Off – On – Off – On.
Check Engine Light Signals: Observe the “check engine” light. It will begin to flash in patterns. Count the flashes to decipher the two-digit codes. For example, “flash-flash (pause) flash-flash-flash (long pause)” indicates code 23. A code 55, represented as “flash-flash-flash-flash-flash (long pause)”, signifies the end of the code sequence and is a normal output. Be patient and watch for pauses to correctly identify the codes. Do not be confused by repeated ’23 23′ flashes, this is likely just code 55 being displayed.

For Newer Jeep Models (OBD-II):

Insert Key and Reset Button: Insert the ignition key and locate the odometer reset button on your instrument cluster.
Press and Turn: Press and hold down the odometer reset button. While holding the button, turn the ignition key to the “RUN” position. This is the position just before starting the engine.
Release Button and Observe Odometer: Release the odometer reset button. The odometer display will cycle through a series of numbers (e.g., 111111 to 999999), then may display the vehicle’s serial number. Following this, it should display any stored diagnostic trouble codes, often prefixed with a “P” (for Powertrain codes).
Alternative OBD-I Method: If the OBD-II key trick method does not work for your newer Jeep, try the OBD-I method described above, as some models may still respond to this older procedure.

Comprehensive List of Jeep OBD-I Codes

Important Note: OBD-I codes can vary, especially for vehicles manufactured around 1996 when OBD-II was being introduced. This list is a general guide and might not be completely exhaustive or perfectly accurate for every specific Jeep model. Always consult your vehicle’s repair manual for the most precise information.

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
13: MAP sensor or vacuum line may not be working
14: MAP sensor voltage below .16V or over 4.96V
15: No speed/distance sensor signal
16: Loss of battery voltage detected with engine running
17: Engine stays cool too long (bad thermostat or coolant sensor?) OR 17 (1985 turbo only): knock sensor circuit
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
25: Automatic Idle Speed (AIS) motor driver circuit shorted or target idle not reached
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 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
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)
34: (1984-86): EGR solenoid circuit shorted or open OR 34 (1987-1991): speed control shorted or open
35: Cooling fan relay circuit open or shorted OR 35: idle switch motor fault – check connections
36 (turbo only): Wastegate control circuit open or shorted
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)
41: Alternator field control circuit open or shorted
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 (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)
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
44: No FJ2 voltage present at logic board OR 44: Logic module self-diagnostics indicate problem OR 44: Battery temperature out of range
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 (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).
52: Oxygen sensor stuck at rich position OR 52 Internal logic module fault (’84 turbo only)
53: Logic module internal 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
55: End of codes
61: “Baro” sensor open or shorted
62: EMR mileage cannot be stored in EEPROM OR 62 PCM failure SRI mile not stored
63: Controller cannot write to EEPROM
64: Catalytic converter efficiency failure
65: Power steering switch failure
66: No CCD Message From TCM and/or No CCD Message From BCM

Comprehensive List of Jeep OBD-II Codes

OBD-II codes are standardized and consist of a five-character alphanumeric code. The letter indicates the system (P for Powertrain, B for Body, C for Chassis, U for Network), followed by a digit indicating whether it’s a generic (0) or manufacturer-specific (1) code, and then three more digits specifying the fault. Here’s a list of common OBD-II codes relevant to Jeeps:

P0030 & P0036: Sensor heater relay problem
P0106: MAP sensor voltage out of range detected at startup
P0107: MAP sensor voltage too low
P0108: MAP sensor voltage too high
P0112: Intake air temperature sensor voltage low
P0113: Intake air (charge) temperature sensor voltage high
P0116: Coolant temperature sensor reading doesn’t make sense
P0117: Engine coolant temperature sensor voltage low
P0118: Engine coolant temperature sensor voltage high
P0121: Throttle position sensor and MAP sensor disagree with each other
P0122: Throttle position sensor voltage low
P0123: Throttle position sensor voltage high
P0125: Taking too long to reach proper operating temperature and switch to energy-efficient mode
P0130 – P0147: O2 Sensor Circuit Malfunction (Bank 1 & 2, Sensor 1, 2, & 3) – various issues like circuit malfunction, low/high voltage, slow response, no activity, heater circuit malfunction.
P0151 – P0160: Oxygen sensor voltage problem – short circuit to ground/active 12V?, response too slow, no rich or lean condition detected, heater element malfunction.
P0161: Oxygen sensor heater element not working properly
P0171 & P0174: System too lean (Bank 1 & 2)
P0172 & P0175: System too rich (Bank 1 & 2)
P0176 – P0179: Flex fuel sensor problems
P0182 & P0183: Compressed natural gas temperature sensor problem
P0201 – P0208: Injector #1 – #8 control circuit problem (open or shorted)
P0300: Misfire detected in multiple cylinders.
P0301 – P0308: Misfire detected in cylinder #1 – #8.
P0320: Crankshaft position sensor reference signal cannot be found while the engine is cranking.
P0325 & P0330: Knock sensor (#1 & #2) signal is wrong.
P0340: No camshaft signal being received by the computer
P0350 – P0358: Coil #1 – #8 issues – drawing too much current or not reaching peak current at the right time.
P0401: EGR insufficient flow detected
P0403: EGR solenoid control circuit problem.
P0404: EGR sensor’s reported position makes no sense
P0405 & P0406: EGR position sensor voltage wrong.
P0412: Secondary air solenoid control circuit bad.
P0420 & P0432: Catalyst efficiency below threshold (Bank 1 & 2).
P0441: Evaporative purge flow system not working properly
P0442: Small leak detected in evaporative system!
P0443: Evaporative purge flow system solenoid not working properly
P0455: Large leak detected in evaporative system!
P0456: Small leak detected in evaporative system!
P0460 & P0461: Fuel level sender not reporting change over distance/time.
P0462 & P0463: Fuel level sender voltage wrong.
P0500: Vehicle speed sensor malfunction.
P0505: Idle air control system malfunction.
P0522 & P0523: Oil pressure sensor problems
P0551: Power steering switch problem.
P0600 – P0605: Internal computer errors (Coprocessors, RAM, ROM).
P0615: Starter relay circuit problem
P0622: Generator field control problem
P0645: A/C clutch relay circuit problem.
P0700: Transmission control system malfunction.
P0703: Brake switch circuit information seems wrong.
P0711 – P0713: Transmission fluid temperature sensor problems (sensor performance/range, voltage low/high).
P0720: Output Shaft Speed Sensor mismatch with vehicle speed.
P0740: Torque converter clutch lock-up system malfunction.
P0743: Torque converter clutch solenoid circuit problem.
P0748: Governor Pressure Solenoid circuit problem (Transmission relay circuit problem in Jeep RE transmissions)
P0751: Overdrive override switch pressed for over five minutes.
P0753: Overdrive solenoid control circuit problem (transmission relay circuit in Jeep RE transmissions.)
P0756: Shift solenoid B (2-3) fault
P0783: Overdrive solenoid unable to engage overdrive gear.
P0801: Transmission reverse gear lockout solenoid circuit problem!
P0833: Clutch-released switch circuit problem?
P1192 & P1193: Inlet air temperature sensor voltage wrong
P1194: Oxygen sensor heater performance faulty
P1195 & P1196: Oxygen sensor slow response (Bank 1 & 2).
P1197: Oxygen sensor switched too slowly (bank 1).
P1198 & P1199: Radiator coolant temperature sensor voltage wrong.
P1281: Engine staying cold too long – check thermostat.
P1282: Fuel pump relay circuit problem.
P1288: Intake manifold short runner tuning valve circuit problem.
P1289: Manifold tuning valve solenoid control circuit problem.
P1290: Compressed natural gas system pressure too high
P1291: Heated air intake sensor malfunction.
P1292 & P1293: Natural gas pressure sensor issue
P1294: Cannot reach target engine speed, check vacuum leaks and idle speed motor issues.
P1295: Throttle position sensor voltage too low.
P1296: MAP sensor voltage too low.
P1297: MAP sensor reading doesn’t change when engine is running!
P1298: Engine runs lean during wide-open throttle.
P1299: MAP Sensor and Throttle Position Sensor signals don’t match, check for vacuum leak.
P1388: Auto shutdown relay circuit problems?
P1389: No Z1 or Z2 voltage seen by the computer when the auto shutdown relay is used.
P1390: Cam and crank signals don’t match – timing belt skipped a tooth?
P1391: Intermittent loss of crank or cam sensor signal.
P1398: Crank Sensor signal present during Misfire Diagnostics preparation.
P1399: Wait to Start Lamp circuit problem – (diesels only?)
P1403: EGR position sensor voltage low.
P1476 & P1477: Too little/much secondary air injection during aspirator test.
P1478: Battery temperature sensor voltage wrong.
P1479: Transmission fan relay circuit problems?
P1480: PCV solenoid circuit problems?
P1481: Transmission RPM pulse generator signal for misfire detection wrong.
P1482 & P1483: Catalyst temperature sensor circuit shorted low/high.
P1484: Catalyst overheating!
P1485: Air injection solenoid circuit problems.
P1486: Pinched or blocked hose in evaporative hose system.
P1487 & P1498: Radiator fan control circuit problems – #2 & #3 high-speed relay control.
P1488: Auxiliary 5-volt sensor feed too low.
P1489: High speed radiator fan control circuit problem.
P1490: Low speed radiator fan control circuit problem.
P1491: Radiator fan control circuit problem (may be solid state relays as well as other circuits).
P1492 & P1493: Ambient or battery temperature sensor voltage wrong
P1494 & P1495: Leak Detection Pump (LDP) pressure switch problems (electrical/pump or solenoid circuit).
P1496: Sensor feed below acceptable limit (under 4v for 4 seconds – should be 5v).
P1594: Voltage too high in charging system.
P1595: Speed control vacuum or vent solenoid control circuits shorted or lost.
P1596: Speed control switch always high
P1597: Speed control switch always low
P1598: A/C pressure sensor voltage high
P1599: A/C pressure sensor voltage low
P1681: No messages received from the cluster control module (dashboard computer).
P1682: Charging system malfunction.
P1683: Speed control servo power control circuit problem.
P1684: Battery disconnected within the last 50 starts (informational, not necessarily an error).
P1685: Invalid key received from the Smart Key Immobilizer Module.
P1686: No messages received from the Smart Key Immobilizer Module.
P1687: No messages received from the Mechanical Instrument Cluster module.
P1693: Companion engine control module fault.
P1694: No messages received from the powertrain control module-Aisin transmission.
P1695: No messages received from the body control module.
P1696 & P1697: Unsuccessful attempt to write to EEPROM location or update Service Reminder Indicator (SRI) mileage!
P1698: No messages received from the electronic transmission control module or the Aisin transmission controller.
P1719: Transmission 2-3 gear lockout solenoid control circuit problem.
P1740: Torque converter clutch solenoid or overdrive solenoid system malfunction.
P1756 & P1757: Transmission control pressure not equal to target (Mid/Zero pressure problem).
P1762 – P1764: Governor Pressure Sensor input problems (too high/low).
P1765: Open or short in the Transmission Relay control circuit.
P1899: Park/Neutral switch stuck!

Disclaimer and Important Notes

It is crucial to understand that these code lists are aids for troubleshooting and not definitive repair guides. While retrieving Jeep OBD2 codes can provide valuable insights into potential problems, it’s essential to remember:

Incomplete Listing: These lists may not be exhaustive, and specific codes can vary slightly depending on the exact Jeep model year and options.
Not Jeep Specific (in some cases): Some codes listed, especially in the OBD-I section, might be more broadly applicable to Chrysler vehicles in general, as mentioned in the original source.
Computer Interpretation: The vehicle’s computer (ECU/PCM) interprets sensor data and may not always perfectly identify the root cause. A code indicates a problem within a system or circuit, but the actual faulty component could be different.
Limp Mode: In severe cases, the computer might activate “Limp In” mode to protect the engine, which can manifest as reduced power or transmission issues (like losing 3rd or 4th gear in automatic transmissions).
Professional Diagnosis Recommended: For accurate diagnosis and repair, especially for complex issues, it is always recommended to consult a qualified mechanic. A professional technician has access to advanced diagnostic tools and expertise to properly interpret codes and address the underlying problems.

Using the key trick and understanding Jeep OBD2 codes is a great starting point for Jeep owners to become more informed about their vehicle’s health. However, always prioritize safety and seek professional help when needed to ensure accurate repairs and maintain your Jeep’s optimal performance.