OBD2 P-Codes Explained: Your Guide to Diagnostic Trouble Codes with a ’97 Probe

Navigating the complexities of modern vehicle diagnostics can be daunting, but understanding your car’s On-Board Diagnostics II (OBD2) system is crucial for maintenance and repair. When your check engine light illuminates, your vehicle is signaling that something is amiss. An OBD2 scanner, sometimes referred to as an OBD2 probe, is your key to unlocking the mystery behind that warning light. This article delves into the world of OBD2 P-codes, particularly focusing on a range of codes that might be relevant when using a ’97 probe or similar diagnostic tools on OBD2 compliant vehicles.

Understanding OBD2 and P-Codes

The OBD2 system is standardized across most vehicles manufactured since 1996. It’s designed to monitor various systems within your car, from the engine and transmission to emissions control. When the system detects a problem, it stores a Diagnostic Trouble Code (DTC) and often activates the check engine light. These DTCs are categorized into several groups, with “P-codes” specifically indicating issues within the powertrain system – encompassing the engine, transmission, and related components.

Using an OBD2 scanner, like a ’97 probe-style tool, allows you to retrieve these P-codes and begin the diagnostic process. While ’97 probe might refer to the era when OBD2 was becoming standard, the principles of reading and interpreting these codes remain consistent across various OBD2 compliant vehicles and scanners.

Exploring Common OBD2 P-Codes (P1479 – P1901 Range)

The range of P-codes from P1479 to P1901 covers a diverse set of potential issues, primarily related to emissions control systems, idle control, vehicle speed sensing, and transmission functions. Let’s break down some key areas within this range:

Emissions Control System Faults: EGR and Related Solenoids

Several codes in this range pinpoint problems within the Exhaust Gas Recirculation (EGR) system. The EGR system is vital for reducing harmful nitrogen oxide (NOx) emissions by recirculating a portion of exhaust gas back into the engine intake. Codes you might encounter include:

• P1479 Fan Control (Condenser Primary) Circuit: While seemingly unrelated to EGR directly, fan control issues can impact overall engine temperature and indirectly affect emissions systems.
• P1485 EGR Vacuum Solenoid Circuit, P1486 EGR Vent Solenoid Circuit, P1487 EGR-CHK (Boost) Solenoid Circuit: These codes indicate electrical circuit problems with various solenoids that control the EGR system’s vacuum and venting functions. Solenoids are essentially electrically controlled valves, and failures can stem from wiring issues, faulty solenoids, or PCM (Powertrain Control Module) problems.
• P1496, P1497, P1498, P1499 EGR Valve Motor Coil ‘1’ – ‘4’ Open or Shorted: Modern EGR valves often use electric motors for precise control. These codes signal electrical faults within the motor coils of the EGR valve itself, potentially leading to valve malfunction and incorrect EGR flow.
• P1540 ABV System Fault, P1525 ABV Vacuum Solenoid Circuit, P1526 ABV Vent Solenoid Circuit: ABV might refer to an Auxiliary Bypass Valve or Air Bypass Valve, often related to emissions or intake air control. These codes point to faults in the ABV system, vacuum solenoids controlling it, or venting circuits.

Alt text: A handheld OBD2 scanner tool displaying diagnostic information, commonly used to read fault codes from a vehicle’s OBD2 port.

Idle Air Control (IAC) and Related Systems

Proper idle speed is crucial for smooth engine operation. The Idle Air Control (IAC) system regulates airflow to maintain a stable idle. Codes in this range related to idle control include:

• P1504 Idle Air Control Solenoid Circuit Intermittent: Indicates an intermittent electrical problem in the IAC solenoid circuit, which controls the IAC valve.
• P1505 Idle Air Control System at Adaptive Clip: This suggests the IAC system has reached its maximum adjustment limit to maintain idle speed, possibly indicating a larger underlying issue like vacuum leaks or throttle body problems.
• P1506 Idle Air Control System Overspeed Detected, P1507 Idle Air Control System Underspeed Detected: These codes signal that the engine idle speed is either too high or too low, pointing to potential IAC system malfunctions, vacuum leaks, or other engine control issues.
• P1508 Bypass Air Solenoid ‘1’ Circuit, P1509 Bypass Air Solenoid ‘2 Circuit: Similar to IAC, bypass air solenoids can be used to control airflow for idle or other engine management purposes. These codes suggest electrical circuit problems with these solenoids.

Vehicle Speed Sensor (VSS) Issues

The Vehicle Speed Sensor (VSS) provides crucial speed information to the PCM and other vehicle systems like the transmission and ABS. Codes related to VSS include:

• P1500 Vehicle Speed Sensor Intermittent Signal, P1501 Vehicle Speed Sensor Out of Self Test Range, P1502 Vehicle Speed Sensor Circuit Error: These codes all point to problems with the VSS circuit or the signal it’s sending. Intermittent signals, out-of-range readings, or general circuit errors can stem from sensor failure, wiring issues, or problems with the PCM receiving the signal. VSS problems can affect speedometer readings, transmission shifting, and cruise control operation.

Alt text: Diagram showing a typical location of a vehicle speed sensor on a car’s transmission, highlighting its role in monitoring vehicle speed for engine and transmission control systems.

Transmission Related Codes (P1701 – P1797 Range)

A significant portion of the P1479-P1901 range focuses on transmission-related issues. These codes can indicate problems with the transmission range sensor, fluid temperature sensor, shift solenoids, torque converter clutch, and various electrical circuits within the transmission control system. Examples include:

• P1701 Transmission Range Sensor Reverse Engagement Error, P1702 Transmission Range Sensor Circuit Intermittent, P1705 Transmission Range Sensor out of Self Test Range: The transmission range sensor (also known as a neutral safety switch or gear position sensor) tells the PCM which gear the transmission is in. These codes indicate errors in the sensor’s signal when engaging reverse or general circuit faults.
• P1711 Transmission Fluid Temperature Sensor Circuit out of Self Test Range, P1713 Transmission Fluid Temperature Sensor Circuit, P1718 Transmission Fluid Temperature Sensor Circuit, P1783 Transmission Fluid Temperature High Input: Transmission fluid temperature is critical for proper transmission operation. These codes signal problems with the transmission fluid temperature sensor circuit or readings that are out of range, including excessively high temperatures. Overheating transmission fluid can lead to severe damage.
• P1714 Shift Solenoid ‘1’ Mechanical Fault, P1715 Shift Solenoid ‘2’ Mechanical Fault, P1716 Shift Solenoid ‘3’ Mechanical Fault, P1717 Shift Solenoid ‘4’ Mechanical Fault, P1751 Transmission Shift Solenoid ‘A’ Mechanical Fault, P1756 Transmission Shift Solenoid ‘B’ Mechanical Fault, P1761 Transmission Shift Solenoid ‘3’ Mechanical Fault: Shift solenoids are electrically controlled valves that direct hydraulic fluid within the transmission to change gears. These “mechanical fault” codes often indicate that a solenoid is stuck, either open or closed, preventing proper gear shifting.
• P1740 Torque Converter Clutch Solenoid Mechanical Fault, P1741 Torque Converter Clutch Control Electrical Fault, P1742 Torque Converter Clutch Solenoid Shorted, P1743 Torque Converter Clutch Failed On – TCIL is On, P1744 Torque Converter Clutch Solenoid Mechanical Fault, P1767 Torque Converter Clutch Solenoid Circuit: The torque converter clutch (TCC) improves fuel economy by creating a direct mechanical link between the engine and transmission at cruising speeds. These codes point to various electrical and mechanical problems within the TCC solenoid and control circuit.
• P1746 Electronic Pressure Control Solenoid Circuit Open, P1747 Electronic Pressure Control Solenoid Circuit, P1749 Electronic Pressure Control Solenoid Circuit Low: Electronic pressure control (EPC) solenoids regulate hydraulic pressure within the transmission for smooth shifting. These codes indicate electrical circuit issues with the EPC solenoid, such as open circuits, shorts, or low voltage.
• P1771 Throttle Position Sensor Circuit Open to Transmission Control Module, P1772 Throttle Position Sensor Circuit Shorted to Transmission Control Module: The Throttle Position Sensor (TPS) signal is used by both the engine and transmission control modules. These codes indicate problems with the TPS signal specifically as it relates to the transmission control module, suggesting wiring or sensor issues affecting the signal reaching the TCM.
• P1780 Transmission Control Switch Circuit, P1780 Overdrive Off Switch not Cycled during the Self Test, P1781 Transmission 4×4 Low Switch out of Range Fault, P1797 P/N Switch Open or Short Circuit: These codes relate to various switches that provide input to the transmission control system, such as the overdrive off switch, 4×4 low switch, and Park/Neutral (P/N) switch. Problems in these circuits can affect transmission operation and mode selection.

Other Powertrain Related Codes

The P1479-P1901 range also includes codes related to other powertrain components and systems:

• P1512 VTCS Fault, P1569 VTCS Circuit Low Input, P1570 VTCS Circuit High Input: VTCS likely refers to Variable Tumble Control System or Variable Turbine Control System. These codes indicate faults within this system and electrical circuit issues (low or high input signals).
• P1521 VRIS Solenoid ‘1’ Circuit, P1522 VRIS Solenoid ‘2 Circuit: VRIS likely refers to Variable Resonance Induction System. These codes indicate electrical circuit problems with solenoids controlling the VRIS, which optimizes intake airflow for different engine speeds.
• P1523 VICS Solenoid Circuit: VICS likely refers to Variable Intake Control System. This code indicates an electrical circuit problem with the solenoid controlling the VICS, similar in function to VRIS.
• P1524 Charge Air Cooler Bypass Solenoid Circuit: If your vehicle is turbocharged or supercharged, this code might relate to the charge air cooler (intercooler) bypass solenoid, which could control airflow around the intercooler.
• P1529 L/C Atmospheric Balance Air Control Valve Circuit: L/C is unclear without more context, but this code points to a circuit problem with an atmospheric balance air control valve, possibly related to emissions or fuel vapor recovery.
• P1562 Powertrain Control Module +BB Voltage Low, P1794 Powertrain Control Module Battery Direct Power Circuit: These codes indicate issues with the power supply to the Powertrain Control Module (PCM). Low voltage or problems in the direct battery power circuit can cause a wide range of malfunctions as the PCM is the central computer controlling engine and transmission functions.
• P1601, P1602 Powertrain Control Module Communication Line to TCM Error, P1627, P1628 Powertrain Control Module (ECM/TCS) Line Communication Error: These codes indicate communication problems between the PCM (or ECM – Engine Control Module) and the Transmission Control Module (TCM) or Traction Control System (TCS). Communication issues can arise from wiring problems, module failures, or CAN bus problems.
• P1602 Immobilizer System Communication Error with Powertrain Control Module, P1603, P1604, P1621, P1622, P1623, P1624 Immobilizer System Fault: These codes indicate various faults within the immobilizer system, which is a security system designed to prevent vehicle theft. Communication errors between the immobilizer and PCM or general immobilizer system malfunctions can prevent the engine from starting.
• P1605 Powertrain Control Module Keep Alive Memory Test Error, P1608 Powertrain Control Module (ECM CPU) DTC Test Fault, P1609 Powertrain Control Module (ECM CPU) Knock Sensor Circuit: These codes suggest internal problems within the PCM itself, such as Keep Alive Memory (KAM) errors, CPU test faults, or issues with the knock sensor circuit within the PCM.
• P1631 Generator Output Voltage Signal (No Output), P1632 Battery Voltage Monitor Circuit, P1633 Battery Overcharge Fault, P1634 Generator Terminal ‘B’ Circuit Open: These codes relate to the charging system. Problems with the generator (alternator) output, battery voltage monitoring circuit, overcharging, or open circuits in the generator terminal can indicate charging system malfunctions.
• P1650 Power Steering Pressure Switch Out of Range Fault, P1651 Power Steering Pressure Switch Circuit, P1652 Power Steering Pressure Switch Circuit: The power steering pressure switch is often used to signal the PCM when the power steering system is under load, allowing the engine to compensate with slightly higher idle speed. These codes point to problems with the pressure switch circuit or out-of-range readings.
• P1900 Turbine Speed Sensor Circuit Intermittent, P1901 Torque Converter Clutch Circuit Intermittent: These codes indicate intermittent signal issues with the turbine speed sensor (often used in automatic transmissions) and the torque converter clutch circuit, suggesting wiring or sensor problems that occur sporadically.

Diagnosing and Resolving P-Codes

When you retrieve a P-code using your OBD2 scanner, it’s just the first step. A P-code provides a starting point for diagnosis, not a definitive solution. Here’s a general approach:

1. Record the Code: Write down the exact code and its description.
2. Research the Code: Use reliable online resources or repair manuals to understand the potential causes and symptoms associated with the specific P-code. Websites like cardiagnosticnearme.com are excellent resources for this!
3. Visual Inspection: Check for obvious issues like loose wiring, disconnected vacuum lines, damaged sensors, or fluid leaks in the system related to the code.
4. Component Testing: Depending on the code, you may need to test components like solenoids, sensors, or circuits using a multimeter or other diagnostic tools.
5. Professional Help: If you’re not comfortable with automotive diagnostics or repairs, it’s always best to consult a qualified mechanic.

Conclusion

Understanding OBD2 P-codes is essential for modern vehicle maintenance. Using an OBD2 probe or scanner to retrieve these codes empowers you to take a proactive approach to vehicle care. While the range of P1479-P1901 covers a broad spectrum of potential issues, focusing on system areas like emissions control, idle control, vehicle speed sensing, and transmission functions can help narrow down the diagnostic process. Remember to always research codes thoroughly and seek professional help when needed to ensure accurate diagnosis and effective repairs.