Decoding 1990 Ford Probe OBD Codes: A Comprehensive Guide

Navigating car troubles can be frustrating, especially when your trusty 1990 Ford Probe isn’t running as smoothly as it used to. Understanding the diagnostic codes your vehicle might be throwing is the first step towards effective repairs. While the term “OBD2” is commonly used today, it’s important to clarify the diagnostic system relevant to your 1990 Ford Probe. Let’s delve into the world of Ford Probe diagnostics and shed light on those crucial error codes.

Understanding OBD Systems on the 1990 Ford Probe

The 1990 Ford Probe, being an early model, likely utilizes an OBD1 (On-Board Diagnostics 1) system, rather than the more standardized OBD2 system which became commonplace in later years (typically 1996 onwards in the USA). While there might be instances of confusion or overlap in terminology, recognizing this distinction is key. OBD1 systems in vehicles like the 1990 Ford Probe were less standardized across manufacturers, meaning Ford-specific diagnostic procedures and code interpretations are often necessary.

Despite the “OBD2” keyword being frequently searched, understanding the principles of on-board diagnostics, regardless of the specific generation, remains valuable. The codes listed below, while presented in a format that might resemble later OBD systems (P-codes), are relevant to the diagnostic capabilities of your 1990 Ford Probe and its engine management system. These “P-codes” generally refer to Powertrain codes, indicating issues within the engine or transmission.

1990 Ford Probe Diagnostic Trouble Codes (P1479 – P1901)

Here is a breakdown of potential diagnostic trouble codes your 1990 Ford Probe might display, focusing on the P1479 to P1901 range. Please note that accessing and interpreting these codes will require using an appropriate OBD1 scanner or performing specific diagnostic procedures outlined in your Ford Probe repair manual.

• P1479 Fan Control (Condenser Primary) Circuit: Indicates a problem within the primary condenser fan control circuit. This could involve wiring issues, a faulty fan relay, or issues with the fan motor itself.
• P1485 EGR Vacuum Solenoid Circuit: Points to a malfunction in the Exhaust Gas Recirculation (EGR) vacuum solenoid circuit. This solenoid controls vacuum to the EGR valve, and issues here can affect emissions and engine performance.
• P1486 EGR Vent Solenoid Circuit: Similar to P1485, but specifically related to the EGR vent solenoid circuit. This solenoid is also part of the EGR system and its proper function is crucial for emissions control.
• P1487 EGR-CHK (Boost) Solenoid Circuit: This code refers to a problem in the EGR-CHK or boost solenoid circuit, potentially relevant for turbocharged models if applicable, or related to specific EGR system checks.
• P1496 EGR Valve Motor Coil ‘1’ Open or Shorted: Indicates an electrical fault (open or short circuit) in the first coil of the EGR valve motor. This suggests a problem with the EGR valve actuator itself.
• P1497 EGR Valve Motor Coil ‘2’ Open or Shorted: Similar to P1496, but for the second coil of the EGR valve motor.
• P1498 EGR Valve Motor Coil ‘3 Open or Shorted: Similar to P1496 and P1497, but for the third coil of the EGR valve motor.
• P1499 EGR Valve Motor Coil ‘4’ Open or Shorted: Similar to P1496, P1497, and P1498, but for the fourth coil of the EGR valve motor. These P149x codes highlight potential issues within the EGR valve motor itself, requiring inspection of the valve and its electrical connections.

Alt text: A detailed view of a 1990 Ford Probe engine bay, showcasing engine components relevant to diagnostic trouble codes.

• P1500 Vehicle Speed Sensor Intermittent Signal: Signals an intermittent or inconsistent signal from the Vehicle Speed Sensor (VSS). This can affect speedometer readings, transmission shifting, and cruise control operation.
• P1501 Vehicle Speed Sensor Out of Self Test Range: Indicates the VSS signal is outside the expected range during a self-test. This suggests a possible sensor malfunction or wiring issue.
• P1502 Vehicle Speed Sensor Circuit Error: A general error within the VSS circuit, requiring further investigation into wiring, sensor, and connections.
• P1504 Idle Air Control Solenoid Circuit Intermittent: Points to an intermittent fault in the Idle Air Control (IAC) solenoid circuit. The IAC valve controls idle speed, and problems here can cause rough idling or stalling.
• P1505 Idle Air Control System at Adaptive Clip: Indicates the IAC system has reached its adaptive limit, suggesting a potential underlying issue causing the system to compensate excessively.
• P1506 Idle Air Control System Overspeed Detected: The engine idle speed is higher than expected, and the IAC system is unable to control it effectively. This could be due to vacuum leaks, a faulty IAC valve, or other engine issues.
• P1507 Idle Air Control System Underspeed Detected: The engine idle speed is lower than expected, and the IAC system is unable to compensate. Similar to P1506, this could be due to IAC valve problems or other engine-related issues.
• P1508 Bypass Air Solenoid ‘1’ Circuit: Indicates a problem in the circuit for bypass air solenoid ‘1’. This solenoid might be part of the intake or emissions system, depending on the specific engine configuration.
• P1509 Bypass Air Solenoid ‘2 Circuit: Similar to P1508, but for bypass air solenoid ‘2’.
• P1512 VTCS Fault: Refers to a fault in the Variable Tumble Control System (VTCS). VTCS is designed to improve engine efficiency and emissions, and a fault here may impact performance.
• P1521 VRIS Solenoid ‘1’ Circuit: Indicates a problem in the Variable Resonance Induction System (VRIS) solenoid ‘1’ circuit. VRIS optimizes intake airflow for different engine speeds, and malfunctions can affect power delivery.
• P1522 VRIS Solenoid ‘2 Circuit: Similar to P1521, but for VRIS solenoid ‘2’.
• P1523 VICS Solenoid Circuit: Points to a problem in the Variable Intake Control System (VICS) solenoid circuit, another system designed to optimize intake airflow and engine performance.
• P1524 Charge Air Cooler Bypass Solenoid Circuit: Relevant for turbocharged models (if applicable to the 1990 Probe), this code indicates an issue with the charge air cooler bypass solenoid circuit. This system manages airflow through the intercooler.
• P1525 ABV Vacuum Solenoid Circuit: Indicates a fault in the Air Bypass Valve (ABV) vacuum solenoid circuit. The ABV might be part of the turbocharger system (if applicable) or emissions control.
• P1526 ABV Vent Solenoid Circuit: Similar to P1525, but for the ABV vent solenoid circuit.
• P1529 L/C Atmospheric Balance Air Control Valve Circuit: This code is more specific and may relate to a Load Control (L/C) atmospheric balance air control valve circuit, possibly within the emissions or fuel system.
• P1540 ABV System Fault: A more general fault within the Air Bypass Valve (ABV) system, suggesting a broader issue beyond just the solenoid circuit.
• P1562 Powertrain Control Module +BB Voltage Low: Indicates low voltage supply to the Powertrain Control Module (PCM) at the +BB (Battery Bus) terminal. This could be due to a weak battery, poor connections, or wiring issues.
• P1569 VTCS Circuit Low Input: Low input voltage detected in the Variable Tumble Control System (VTCS) circuit.
• P1570 VTCS Circuit High Input: High input voltage detected in the Variable Tumble Control System (VTCS) circuit. P1569 and P1570 suggest electrical problems within the VTCS circuit.
• P1601 Powertrain Control Module Communication Line to TCM Error: Indicates a communication error between the Powertrain Control Module (PCM) and the Transmission Control Module (TCM). This suggests a problem in the data communication network between these modules.
• P1602 Powertrain Control Module Communication Line to TCM Error: Repeats P1601, possibly indicating a persistent or recurring communication issue.
• P1602 Immobilizer System Communication Error with Powertrain Control Module: (Note: Code number overlap with previous code – could be a typo in original list). This different P1602 indicates a communication problem between the immobilizer system and the PCM. This can prevent the engine from starting.
• P1603 Immobilizer System Fault: A general fault within the immobilizer system itself.
• P1604 Immobilizer System Fault: Repeats P1603, potentially indicating a persistent immobilizer fault.
• P1605 Powertrain Control Module Keep Alive Memory Test Error: Indicates an error during the PCM’s Keep Alive Memory (KAM) test. KAM stores learned values and settings, and an error here might suggest PCM issues or power supply problems.
• P1608 Powertrain Control Module (ECM CPU) DTC Test Fault: Fault detected during the PCM’s (Engine Control Module – ECM – is often used interchangeably with PCM) internal Diagnostic Trouble Code (DTC) test. This points to a potential PCM internal malfunction.
• P1609 Powertrain Control Module (ECM CPU) Knock Sensor Circuit: Problem detected in the knock sensor circuit monitored by the PCM (ECM CPU). Knock sensors detect engine knocking or detonation.
• P1621 lmmobilizer System Fault: (Typo in original list – “lmmobilizer” should be “Immobilizer”). Another indication of a fault within the immobilizer system.
• P1622 lmmobilizer System Fault: (Typo in original list). Repeats P1621, persistent immobilizer fault.
• P1623 lmmobilizer System Fault: (Typo in original list). Repeats P1621 and P1622, persistent immobilizer fault.
• P1624 lmmobilizer System Fault: (Typo in original list). Repeats P1621, P1622, and P1623, persistent immobilizer fault. P1621-P1624 codes all point to issues within the vehicle’s immobilizer system.
• P1627 Powertrain Control Module (ECM/TCS) Line Communication Error: Communication error between the PCM (ECM) and the Traction Control System (TCS), if equipped.
• P1628 Powertrain Control Module (ECM/TCS) Any Line Communication Error: More general communication error between the PCM (ECM) and TCS, indicating a broader communication fault.
• P1631 Generator Output Voltage Signal (No Output): Indicates the generator (alternator) is not producing output voltage. This means the battery is not being charged, and the charging system needs to be checked.
• P1632 Battery Voltage Monitor Circuit: Problem in the battery voltage monitor circuit. This circuit provides feedback to the PCM about battery voltage.
• P1633 Battery Overcharge Fault: The system has detected a battery overcharge condition, which can damage the battery and other electrical components.
• P1634 Generator Terminal ‘B’ Circuit Open: Open circuit in the generator (alternator) terminal ‘B’ circuit. Terminal ‘B’ is typically the main output terminal.
• P1650 Power Steering Pressure Switch Out of Range Fault: The signal from the power steering pressure switch is out of the expected range. This switch is often used to increase idle speed when the power steering is under load.
• P1651 Power Steering Pressure Switch Circuit: General fault in the power steering pressure switch circuit.
• P1652 Power Steering Pressure Switch Circuit: Repeats P1651, potentially indicating a persistent issue. P1650-P1652 all point to problems within the power steering pressure switch system.
• P1701 Transmission Range Sensor Reverse Engagement Error: Indicates an error related to the transmission range sensor when engaging reverse. The range sensor indicates the selected gear position to the transmission control system.
• P1702 Transmission Range Sensor Circuit Intermittent: Intermittent fault in the transmission range sensor circuit.
• P1703 Brake On/Off Switch Out of Self Test Range: The brake on/off switch signal is out of the expected range during a self-test. This switch is crucial for torque converter clutch operation and other transmission functions.
• P1705 Transmission Range Sensor out of Self Test Range: The transmission range sensor signal is out of range during a self-test, similar to P1701 but detected during system testing.
• P1709 Clutch Pedal Position Switch Circuit: Fault in the clutch pedal position switch circuit. Relevant for manual transmission models (if applicable to the 1990 Probe in certain markets), this switch is used for engine control and potentially cruise control functions.
• P1711 Transmission Fluid Temperature Sensor Circuit out of Self Test Range: The transmission fluid temperature sensor signal is out of range during self-test.
• P1713 Transmission Fluid Temperature Sensor Circuit: General fault in the transmission fluid temperature sensor circuit. P1711 and P1713 indicate problems with the transmission fluid temperature sensing system, crucial for proper transmission operation.
• P1714 Shift Solenoid ‘1’ Mechanical Fault: Mechanical fault detected in shift solenoid ‘1’ within the transmission. Shift solenoids control hydraulic fluid flow to engage different gears.
• P1715 Shift Solenoid ‘2’ Mechanical Fault: Mechanical fault in shift solenoid ‘2’.
• P1716 Shift Solenoid ‘3’ Mechanical Fault: Mechanical fault in shift solenoid ‘3’.
• P1717 Shift Solenoid ‘4’ Mechanical Fault: Mechanical fault in shift solenoid ‘4’. P1714-P1717 all indicate potential mechanical failures within the transmission shift solenoids.
• P1718 Transmission Fluid Temperature Sensor Circuit: Repeats P1713, persistent issue with the transmission fluid temperature sensor circuit.
• P1720 Vehicle Speed Sensor ‘2’ Signal Error: Error in the signal from a secondary Vehicle Speed Sensor ‘2’. Some vehicles use multiple VSS sensors.
• P1729 Transmission 4×4 Low Switch Error: Fault in the 4×4 low switch circuit. Relevant for 4-wheel drive models (if applicable to the 1990 Probe in certain markets).
• P1740 Torque Converter Clutch Solenoid Mechanical Fault: Mechanical fault in the Torque Converter Clutch (TCC) solenoid. The TCC solenoid controls engagement of the torque converter clutch for improved fuel economy.
• P1741 Torque Converter Clutch Control Electrical Fault: Electrical fault in the TCC control circuit.
• P1742 Torque Converter Clutch Solenoid Shorted: Short circuit in the TCC solenoid.
• P1743 Torque Converter Clutch Failed On – TCIL is On: The Torque Converter Clutch is stuck in the ‘on’ position, and the Transmission Control Indicator Lamp (TCIL) is illuminated (check engine light related to transmission).
• P1744 Torque Converter Clutch Solenoid Mechanical Fault: Repeats P1740, persistent mechanical fault in the TCC solenoid. P1740-P1744 all point to issues within the Torque Converter Clutch system.
• P1746 Electronic Pressure Control Solenoid Circuit Open: Open circuit in the Electronic Pressure Control (EPC) solenoid circuit. The EPC solenoid controls transmission fluid pressure.
• P1747 Electronic Pressure Control Solenoid Circuit: General fault in the EPC solenoid circuit.
• P1749 Electronic Pressure Control Solenoid Circuit Low: Low circuit voltage in the EPC solenoid circuit. P1746-P1749 all indicate electrical issues within the Electronic Pressure Control solenoid system.
• P1751 Transmission Shift Solenoid ‘A’ Mechanical Fault: Mechanical fault in transmission shift solenoid ‘A’. (Note: ‘A’, ‘B’, ‘3’ etc. are often used instead of numerical designations in some systems).
• P1752 Transmission Shift Solenoid ‘A’ Circuit Shorted: Short circuit in transmission shift solenoid ‘A’ circuit.
• P1754 Transmission Coast Clutch Solenoid Electrical Fault: Electrical fault in the transmission coast clutch solenoid circuit. The coast clutch is involved in specific shift operations.
• P1756 Transmission Shift Solenoid ‘B’ Mechanical Fault: Mechanical fault in transmission shift solenoid ‘B’.
• P1757 Transmission Shift Solenoid ‘B’ Circuit Shorted: Short circuit in transmission shift solenoid ‘B’ circuit. P1751-P1757 cover potential faults in transmission shift solenoids ‘A’ and ‘B’ and related circuits.
• P1761 Transmission Shift Solenoid ‘3’ Mechanical Fault: Mechanical fault in transmission shift solenoid ‘3’.
• P1762 Transmission SS3/SS4/OD Band Fault: Fault related to the transmission SS3 (Shift Solenoid 3), SS4 (Shift Solenoid 4), or Overdrive (OD) band. This is a more complex transmission fault indication.
• P1765 Transmission 3-2 Timing Solenoid Valve: Problem with the 3-2 timing solenoid valve in the transmission, which controls timing during 3-2 downshifts.
• P1767 Torque Converter Clutch Solenoid Circuit: Repeats P1741, persistent electrical fault in the TCC solenoid circuit.
• P1771 Throttle Position Sensor Circuit Open to Transmission Control Module: Open circuit in the Throttle Position Sensor (TPS) circuit as it relates to the Transmission Control Module (TCM). The TPS signal is used by the TCM for shift scheduling.
• P1772 Throttle Position Sensor Circuit Shorted to Transmission Control Module: Short circuit in the TPS circuit as it relates to the TCM. P1771 and P1772 indicate issues with the TPS signal being received by the TCM.
• P1780 Transmission Control Switch Circuit: Fault in the Transmission Control Switch circuit. This switch might be an overdrive on/off switch or other transmission mode selector.
• P1780 Overdrive Off Switch not Cycled during the Self Test: (Code number overlap – likely same code, different description for the same issue). The overdrive off switch was not activated during a self-test, potentially indicating a switch or circuit problem.
• P1781 Transmission 4×4 Low Switch out of Range Fault: Similar to P1729, but specifically out of range during testing. Fault in the 4×4 low switch circuit.
• P1783 Transmission Fluid Temperature High Input: High temperature reading from the transmission fluid temperature sensor. This could indicate overheating or a sensor malfunction.
• P1788 3-2T/CCS Circuit Open: Open circuit in the 3-2 Timing/Coast Clutch Solenoid (CCS) circuit.
• P1789 3-2T/CCS Circuit Shorted: Short circuit in the 3-2 Timing/Coast Clutch Solenoid (CCS) circuit. P1788 and P1789 indicate electrical issues with the 3-2 Timing/Coast Clutch Solenoid.
• P1794 Powertrain Control Module Battery Direct Power Circuit: Problem with the direct battery power supply to the Powertrain Control Module (PCM). This is similar to P1562 but may be related to a different power feed or circuit.
• P1797 P/N Switch Open or Short Circuit: Open or short circuit in the Park/Neutral (P/N) switch circuit. The P/N switch indicates if the transmission is in Park or Neutral, crucial for starting and safety systems.
• P1900 Turbine Speed Sensor Circuit Intermittent: Intermittent signal from the Turbine Speed Sensor (TSS) circuit. The TSS measures the input speed of the transmission.
• P1901 Torque Converter Clutch Circuit Intermittent: Intermittent fault in the Torque Converter Clutch (TCC) circuit.

Using an OBD Scanner and Troubleshooting

To diagnose issues on your 1990 Ford Probe, you’ll need to access these diagnostic codes. While OBD2 scanners are common, for a 1990 Ford Probe, you will likely need an OBD1 scanner compatible with Ford systems or utilize specific OBD1 Ford diagnostic procedures. These procedures often involve using a scan tool or, in some cases, even manual code retrieval methods that involve counting flashes of the check engine light. Consult your Ford Probe repair manual for the correct method for your specific model year.

Once you have retrieved the codes, this list provides a starting point for understanding potential problem areas. Remember that code descriptions are guides, not definitive diagnoses. Thorough troubleshooting is essential. This may involve:

• Visual Inspection: Check wiring, connectors, vacuum lines, and components related to the fault code for damage or disconnection.
• Component Testing: Use a multimeter or other diagnostic tools to test the sensors, solenoids, and circuits indicated by the code.
• Consulting a Repair Manual: Your Ford Probe repair manual is an invaluable resource for detailed diagnostic procedures and wiring diagrams.

Disclaimer: Automotive diagnostics and repair can be complex. If you are not comfortable working on your vehicle, it is always recommended to seek the help of a qualified, professional mechanic. This information is for informational purposes only and should not be considered a substitute for professional automotive advice.

By understanding these diagnostic codes and the systems they relate to, you are better equipped to address potential issues with your 1990 Ford Probe and keep it running reliably. Remember to always prioritize safety and consult professional help when needed.