Decoding Your Check Engine Light: A Guide to OBD II Codes and Scanners

Navigating car troubles can be stressful, especially when the check engine light illuminates on your dashboard. This warning light is your vehicle’s way of signaling that something isn’t quite right within its complex systems. While it can be alarming, understanding the basics of car diagnostics, particularly On-Board Diagnostics II (OBD II), can empower you to take informed steps towards resolving the issue. This guide will delve into the world of OBD codes, explore a basic code retrieval method, and highlight the advantages of using OBD II scanners for more accurate and efficient vehicle diagnostics.

Understanding OBD and OBD-II Systems

On-Board Diagnostics (OBD) systems have been a part of vehicle manufacturing for decades, evolving to become increasingly sophisticated. Initially, OBD-I systems were manufacturer-specific and lacked standardization, making it challenging for mechanics and car owners to interpret diagnostic information universally. The introduction of OBD-II in the mid-1990s marked a significant leap forward. OBD-II brought standardized diagnostic trouble codes (DTCs), a universal connector, and improved diagnostic capabilities, becoming mandatory for most vehicles sold in the United States and other parts of the world. This standardization allows for greater accessibility to vehicle health information, regardless of make or model.

The “Key Trick” Method: A Basic Code Retrieval Technique

Before the widespread use of affordable OBD II scanners, a method known as the “key trick” was a common way to retrieve basic error codes from some vehicles, particularly Chrysler models. It’s important to note that this method is less reliable and provides far less information than a dedicated OBD II scanner, but it can offer a starting point for older vehicles or in situations where a scanner isn’t immediately available.

For Older (OBD-I) Models:

1. Ensure the ignition is off.
2. Within five seconds, cycle the ignition key between the “On” and “Off” positions three times, ending in the “On” position. (“On” is the position right before starting the engine; “Off” is not “Lock”).
3. Observe the “check engine” light. It will begin to flash in a sequence.
4. Count the flashes. Two-digit codes are indicated by flashes separated by pauses. For example, code 23 would be FLASH FLASH (pause) FLASH FLASH FLASH (long pause). A code 55 (end of codes) is normal.

Important Notes for OBD-I “Key Trick”:

• Setting the parking brake might be necessary for codes to display on some models.
• Blink spacing can be inconsistent on older models, so carefully observe pauses.
• Codes are not typically repeated; seeing “23 23” might indicate a single code 55 (end of codes).

For Newer (OBD-II) Models (Key and Odometer Method):

1. Insert the key into the ignition.
2. Press and hold the odometer reset button.
3. Turn the key to the “RUN” position (without starting the engine) while still holding the button.
4. Release the odometer reset button.
5. The odometer display will cycle through numbers (e.g., 111111 to 999999) and may show the car’s serial number.
6. Error codes may then be displayed on the odometer, often starting with a “P” (for powertrain codes).

Important Notes for OBD-II “Key/Odometer Trick”:

• This method is not universally compatible with all OBD-II vehicles. If it doesn’t work, consider trying the OBD-I method or, more effectively, using an OBD II scanner.

Disclaimer Regarding “Key Trick” Methods: These methods are provided for informational purposes only and may not be accurate or reliable for all vehicles. They should not be considered a substitute for professional diagnostic tools and expertise.

Introduction to OBD II Scanners: Enhanced Diagnostics

While “key trick” methods offer a rudimentary way to access some error codes, OBD II scanners provide a far more comprehensive, accurate, and user-friendly approach to vehicle diagnostics. OBD II scanners range from basic handheld code readers to advanced professional-grade scan tools, offering a variety of features and capabilities to suit different needs and budgets.

Benefits of Using an OBD II Scanner:

• Accuracy: Scanners directly communicate with your vehicle’s Engine Control Unit (ECU) and other modules, retrieving precise diagnostic trouble codes and live data.
• Detailed Information: Beyond just code numbers, scanners often provide code definitions, potential causes, and even troubleshooting tips.
• Live Data Streaming: Many scanners can display real-time sensor data (e.g., engine temperature, RPM, oxygen sensor readings), allowing for a deeper understanding of vehicle performance and problem areas.
• Code Clearing: After addressing a problem, scanners can typically clear stored error codes and turn off the check engine light.
• Efficiency: Scanners streamline the diagnostic process, saving time and potentially money compared to relying solely on less accurate methods or guesswork.

For car owners and DIY enthusiasts, a basic OBD II scanner can be an invaluable tool for understanding and addressing common vehicle issues. For professional mechanics, advanced scan tools offer even more in-depth diagnostic capabilities, including advanced system tests, bi-directional controls, and access to manufacturer-specific data.

Common OBD-I Error Codes (Chrysler/Jeep – Circa 1984-1995)

Important Note: OBD-I codes can vary across manufacturers and even within model years. This list is specific to Chrysler/Jeep vehicles from approximately 1984 to 1995. Codes may differ for newer vehicles starting around 1996 and later OBD-II systems.

• 11: No ignition reference signal during cranking; timing belt skipped; camshaft or crankshaft position sensor issue.
• 12: Battery or computer recently disconnected.
• 13: MAP sensor or vacuum line problem.
• 14: MAP sensor voltage low or high.
• 15: No speed/distance sensor signal.
• 16: Loss of battery voltage with engine running.
• 17: Engine stays cool too long (thermostat or coolant sensor?); (1985 turbo only): knock sensor circuit.
• 21: Oxygen sensor signal stuck lean (4.3-4.5V), likely bad sensor.
• 22: Coolant sensor signal out of range.
• 23: Incoming air temperature sensor issue.
• 24: Throttle position sensor voltage high.
• 25: Automatic Idle Speed (AIS) motor circuit shorted or idle not reached.
• 26: Peak injector circuit voltage not reached (check computer signals, voltage regulator, injectors).
• 27: Injector circuit not switching (TBI); (MPI) injector circuit #1 issue; (turbo) injector circuit #2 issue; (1990-) injector output driver problem.
• 31: Evaporator purge solenoid circuit or driver problem.
• 32: (1984 only) power loss/limited lamp or circuit; EGR gases not working (1988); (1990-92) computer didn’t see EGR activation effect on air/fuel ratio.
• 33: Air conditioning clutch relay circuit open or shorted.
• 34: (1984-86) EGR solenoid circuit shorted/open; (1987-1991) speed control shorted/open.
• 35: Cooling fan relay circuit open/shorted; idle switch motor fault.
• 36: (turbo only) Wastegate control circuit open/shorted.
• 37: Shift indicator light failure (5-speed); part throttle lock/unlock solenoid driver circuit (87-89); solenoid coil circuit (85-87 Turbo); Trans temperature sensor voltage low (1995+).
• 41: Alternator field control circuit open/shorted.
• 42: Automatic shutdown relay circuit open/shorted; Fuel pump relay control circuit; Fuel level unit – no change; Z1 voltage missing when autoshutdown energized.
• 43: Peak primary coil current not achieved; Cylinder misfire; Power module to logic module interface problem.
• 44: No FJ2 voltage at logic board; Logic module self-diagnostics problem; Battery temperature out of range.
• 45: Turbo boost limit exceeded (engine shut down).
• 46: Battery voltage too high or charging system voltage too low.
• 47: Battery voltage too low and alternator output too low.
• 51: Oxygen sensor stuck lean; Internal logic module fault (’84 turbo only).
• 52: Oxygen sensor stuck rich; Internal logic module fault (’84 turbo only).
• 53: Logic module internal problem.
• 54: No sync pickup signal during rotation (turbo); Internal logic module fault (’84 turbo); camshaft sensor/distributor timing.
• 55: End of codes (normal).
• 61: “Baro” sensor open or shorted.
• 62: EMR mileage cannot be stored in EEPROM; 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 BCM.

Common OBD-II Error Codes (Generic – P0XXX, P2XXX)

Important Note: OBD-II codes are standardized across manufacturers, but specific diagnostic steps and repair procedures will vary depending on your vehicle’s make and model. This is a general list of common OBD-II codes. For detailed diagnostics, always consult your vehicle’s repair manual or a qualified mechanic.

• P0030, P0036, P0130, P0136, P0142, P0147, P0155, P0161: Sensor heater relay problem; O2 Sensor Circuit Malfunction/Heater Circuit Malfunction (Bank 1/2 Sensor 1/2/3).
• P0106: MAP sensor voltage out of range at startup.
• P0107: MAP sensor voltage too low.
• P0108: MAP sensor voltage too high.
• P0112: Intake air temperature sensor voltage low.
• P0113: Intake air temperature sensor voltage high.
• P0116: Coolant temperature sensor reading illogical.
• P0117: Engine coolant temperature sensor voltage low.
• P0118: Engine coolant temperature sensor voltage high.
• P0121: Throttle position sensor and MAP sensor disagreement.
• P0122: Throttle position sensor voltage low.
• P0123: Throttle position sensor voltage high.
• P0125: Extended time to reach closed loop temperature.
• P0131, P0137, P0143: O2 Sensor Circuit Low Voltage (Bank 1/2 Sensor 1/2/3).
• P0132, P0138, P0144: O2 Sensor Circuit High Voltage (Bank 1/2 Sensor 1/2/3).
• P0133, P0139, P0145: O2 Sensor Circuit Slow Response (Bank 1/2 Sensor 1/2/3).
• P0134, P0140, P0146: O2 Sensor Circuit No Activity Detected (Bank 1/2 Sensor 1/2/3).
• P0141, P0147: O2 Sensor Heater Circuit Malfunction (Bank 1/2 Sensor 2).
• P0151, P0157: Oxygen sensor voltage problem – short circuit to ground?
• P0152, P0158: Oxygen sensor voltage problem – short circuit to active 12V?
• P0153, P0159: Oxygen sensor response too slow.
• P0154, P0160: Oxygen sensor no rich/lean condition – replacement needed?
• 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, P0178, P0179: Flex fuel sensor problem.
• 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 missing during cranking.
• P0325, P0330: Knock sensor (#1/2) signal incorrect.
• P0340: No camshaft signal.
• P0350 – P0358: Coil #1-#8 primary/secondary circuit malfunction; Coil not reaching peak current.
• P0401: Insufficient EGR flow detected.
• P0403: EGR solenoid control circuit problem.
• P0404: EGR sensor position illogical.
• P0405, P0406: EGR position sensor voltage incorrect.
• P0412: Secondary air solenoid control circuit problem.
• P0420, P0432: Catalyst system efficiency below threshold (Bank 1/2).
• P0441: Evaporative purge flow system malfunction.
• P0442: Evaporative system small leak detected.
• P0443: Evaporative purge flow system solenoid malfunction.
• P0455: Evaporative system large leak detected.
• P0456: Evaporative system very small leak detected.
• P0460, P0461: Fuel level sender issue – no change reported.
• P0462, P0463: Fuel level sender voltage incorrect.
• P0500: Vehicle speed sensor malfunction.
• P0505: Idle air control system malfunction.
• P0522, P0523: Oil pressure sensor problem (low/high voltage).
• P0551: Power steering switch problem.
• P0600, P0601, P0604, P0605: Internal control module (PCM/ECM) error.
• 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 incorrect.
• P0711: Transmission fluid temperature sensor performance problem.
• P0712, P0713: Transmission fluid temperature sensor voltage incorrect.
• P0720: Output shaft speed sensor mismatch.
• P0740: Torque converter clutch circuit malfunction.
• P0743: Torque converter clutch solenoid electrical fault.
• P0748: Governor Pressure Solenoid circuit problem (Transmission relay circuit in Jeep RE transmissions).
• P0751: Overdrive override switch pressed too long.
• P0753: Overdrive solenoid control circuit problem (transmission relay circuit in Jeep RE transmissions).
• P0756: Shift solenoid B (2-3) fault.
• P0783: Overdrive solenoid issue – cannot shift to overdrive.
• P0801: Transmission reverse gear lockout solenoid circuit problem.
• P0833: Clutch-released switch circuit problem?
• P1192, P1193: Inlet air temperature sensor voltage incorrect.
• P1194: Oxygen sensor heater performance faulty.
• P1195, P1196, P1197: Oxygen sensor slow response (Bank 1/2).
• P1198, P1199: Radiator coolant temperature sensor voltage incorrect.
• P1281: Engine staying cold too long (thermostat).
• P1282: Fuel pump relay circuit problem.
• P1288, P1289: Intake manifold runner tuning valve 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 idle speed.
• P1295: Throttle position sensor voltage low.
• P1296: MAP sensor voltage low.
• P1297: MAP sensor reading not changing.
• P1298: Engine running lean at wide-open throttle.
• P1299: MAP Sensor and Throttle Position Sensor mismatch.
• P1388: Auto shutdown relay circuit problem.
• P1389: No Z1 or Z2 voltage when auto shutdown relay used.
• P1390: Cam and crank signals mismatch – timing belt skipped?
• P1391: Intermittent crank or cam sensor signal loss.
• P1398: Crank Sensor signal present during Misfire Diagnostics – replace sensor.
• P1399: Wait to Start Lamp circuit problem (diesels?).
• P1403: EGR position sensor voltage low.
• P1476, P1477: Secondary air injection issue during aspirator test (too little/too much air).
• P1478: Battery temperature sensor voltage incorrect.
• P1479: Transmission fan relay circuit problem.
• P1480: PCV solenoid circuit problem.
• P1481: Transmission RPM pulse generator signal wrong.
• P1482, P1483: Catalyst temperature sensor circuit shorted (low/high).
• P1484: Catalyst overheating.
• P1485: Air injection solenoid circuit problem.
• P1486: Evaporative hose system pinched or blocked.
• P1487, P1489, P1490, P1491, P1498: Radiator fan control circuit problems.
• P1488: Auxiliary 5-volt sensor feed too low.
• P1492, P1493: Ambient or battery temperature sensor voltage incorrect.
• P1494, P1495: Leak Detection Pump (LDP) pressure switch problem.
• P1496: Sensor feed voltage below limit.
• P1594: Charging system voltage too high.
• P1595, P1596, P1597: Speed control vacuum/vent solenoid control circuits or switch problems.
• P1598, P1599: A/C pressure sensor voltage incorrect.
• P1681, P1686, P1687, P1694, P1695, P1698: Communication error with various control modules (Cluster, Smart Key Immobilizer, Mechanical Instrument Cluster, Powertrain, Body, Transmission).
• P1682: Charging system malfunction.
• P1683: Speed control servo power control circuit problem.
• P1684: Battery disconnected within 50 starts (informational, not necessarily an error).
• P1685: Invalid key from Smart Key Immobilizer Module.
• P1693: Companion engine control module fault.
• P1696, P1697: EEPROM write error/SRI mileage update failure.
• P1719: Transmission 2-3 gear lockout solenoid circuit problem.
• P1740: Torque converter clutch or overdrive solenoid illogical.
• P1756, P1757: Transmission control pressure not equal to target.
• P1762, P1763, P1764: Governor Pressure Sensor input incorrect.
• P1765: Transmission Relay control circuit open or short.
• P1899: Park/Neutral switch stuck.

Choosing the Right OBD II Scanner for You

Selecting the best OBD II scanner depends on your needs and technical expertise. For basic check engine light diagnosis and code clearing, a simple handheld code reader can be sufficient and affordable. These entry-level scanners typically provide code definitions and may offer basic live data viewing.

For more in-depth diagnostics, advanced features, and professional use, consider scanners with:

• Enhanced Code Definitions and Troubleshooting: Look for scanners that provide more detailed code descriptions, potential causes, and repair tips.
• Live Data Streaming and Graphing: Real-time data display and graphical representations are crucial for understanding sensor behavior and diagnosing intermittent issues.
• Bi-directional Controls: Advanced scanners may offer bi-directional control, allowing you to command certain vehicle functions (e.g., activate solenoids, run tests) for more comprehensive diagnostics.
• ABS and SRS Diagnostics: Some scanners extend beyond engine codes to diagnose Anti-lock Braking System (ABS) and Supplemental Restraint System (SRS/Airbag) issues.
• Manufacturer-Specific Codes: Higher-end scanners may access manufacturer-specific codes for deeper diagnostics on particular makes and models.

Explore OBD II Scanners at obd2scanner.store: To find the perfect OBD II scanner for your diagnostic needs, visit our website at obd2scanner.store. We offer a wide selection of scanners to suit various budgets and requirements, helping you take control of your vehicle’s health.

Conclusion: Empowering Vehicle Diagnostics with OBD II

Understanding OBD II codes and utilizing OBD II scanners empowers car owners and professionals alike to effectively diagnose and address vehicle issues. While basic methods like the “key trick” can offer limited insights, OBD II scanners provide the accuracy, detail, and efficiency needed for modern vehicle diagnostics. By investing in an OBD II scanner and familiarizing yourself with common error codes, you can gain valuable knowledge about your vehicle’s health, make informed repair decisions, and potentially save time and money on automotive maintenance. Remember, while OBD tools are incredibly helpful for diagnosis, complex issues may still require the expertise of a qualified mechanic.