While modern vehicles rely heavily on OBD2 (On-Board Diagnostics II) systems and adapters for troubleshooting, diagnosing your classic 1987 Nissan Pathfinder or Hardbody pickup requires a different approach. If you’re searching for a “1987 Nissan Obd2 Adapter”, it’s important to understand that these early models predate the standardized OBD2 system. Instead of plugging in an adapter, you’ll be utilizing the vehicle’s Engine Control Unit (ECU) directly to retrieve valuable diagnostic information. This guide will walk you through the process of accessing and interpreting ECU error codes on your 1987-1995 Nissan Pathfinder and Hardbody pickups, ensuring you can effectively diagnose issues and keep your vintage Nissan running smoothly.
The ECU on these Nissan models is strategically located beneath the passenger’s side seat. Accessing it is straightforward: simply slide the seat fully forward and remove the plastic cover that protects the ECU. For even easier access, you can opt to remove the seat entirely, providing a completely unobstructed workspace.
The method for engaging the diagnostic mode varies slightly depending on your engine type. VG30i ECUs feature a small toggle switch on the side, concealed by a snap-in cover. Conversely, both 4-cylinder ECUs and VG30E ECUs utilize a slotted switch that requires a quarter or half turn clockwise or counterclockwise to activate the diagnostic functions. It’s worth noting that some early 4-cylinder Hardbody pickup ECUs might also be equipped with the toggle switch. Regardless of the specific type, your ECU will have one of these diagnostic selectors.
Seat removed; ECU in place on the floor with cover. The cover has ONE screw holding it down. Remove that and the cover will pull off.
Diagnostic selector switch with cover installed
Diagnostic selector switch with switch cover removed and set on top of the ECU.
This is where the LED lights are visible on top of the ECU.
Reading Error Codes for 4-Cylinder Nissan Engines
Follow these steps to retrieve error codes from 4-cylinder Nissan Pathfinders and Hardbody pickups:
- Ignition ON: Turn the ignition key to the “ON” position, but do not start the engine. Ensure all dashboard lights are illuminated.
- Engage Diagnostic Mode: Locate the ‘diagnostic mode selector’ screw on the ECU. Turn it fully clockwise. The check engine light on your dashboard should turn off. Wait for 5 seconds.
- Activate Code Reading: After the 5-second wait, turn the ‘diagnostic mode selector’ screw fully counter-clockwise.
- Interpret the Flashing Check Engine Light: The check engine light will now begin to flash a sequence of codes. The number of long flashes indicates the first digit of the code, and the number of short flashes represents the second digit. For example, three long flashes followed by two short flashes would indicate code 32. Carefully note down each code as it is displayed.
- Clear Stored Codes (Optional): If you wish to clear the stored error codes and turn off the check engine light after diagnosis, turn the ‘diagnostic mode selector’ screw fully clockwise while it is in diagnostic mode (flashing codes). Wait 5 seconds, then turn the screw fully counter-clockwise again.
- Retain Stored Codes (Optional): To keep the codes stored in the ECU’s memory and leave the check engine light illuminated, simply turn the ignition key to the “OFF” position while the check engine light is flashing the codes.
Reading Error Codes for V6 Nissan Engines
The process for retrieving codes from V6 engines (VG30i and VG30E) is slightly different:
For VG30i Engines:
- Ignition ON: Turn the ignition key to the “ON” position, without starting the engine. All dashboard lights should be lit.
- Access Diagnostic Switch: Locate the small plastic tab on the side of the ECU (facing the door) and pull it off. Behind it, you’ll find a small toggle switch with “ON” and “DIAGNOSTICS” positions.
- Select Diagnostic Mode: Using a small screwdriver or similar tool, move the toggle switch to the “DIAGNOSTICS” position. Observe the red and green LEDs on top of the ECU. They will blink simultaneously, indicating the diagnostic mode. The LEDs will blink once, pause, then twice, then three times, and so on, cycling through modes 1 to 5. Mode 3 is the most commonly used for retrieving trouble codes.
- Select Mode 3: After the LEDs have blinked three times simultaneously (indicating Mode 3), move the toggle switch back to the “ON” position.
- Interpret LED Flash Codes: After approximately five seconds, the ECU will begin outputting diagnostic codes. The red LED flashes to indicate the tens digit, and the green LED flashes for the ones digit. For example, one red flash followed by two green flashes signifies code 12. Record each code as it is displayed.
- Clear ECU Codes (Optional): To clear trouble codes from the ECU, move the switch to the “DIAGNOSTICS” position and then back to the “ON” position. Finally, turn the ignition key to the “OFF” position.
For VG30E Engines (with slotted switch):
- Ignition ON: Turn the ignition key to the “ON” position, engine off, and all dashboard lights on.
- Engage Diagnostic Mode: Turn the ‘diagnostic mode selector’ screw on the ECU fully clockwise. The check engine light should turn off. Wait 5 seconds.
- Activate Code Reading: Turn the screw fully counter-clockwise.
- Interpret Check Engine Light Flashes: The check engine light will flash error codes in the same manner as described for 4-cylinder engines (long flashes for tens, short flashes for ones).
- Clear Codes (Optional): Follow the same code clearing procedure as for 4-cylinder engines.
1986.5-1995 Nissan ECU Flash Codes (All Engines)
Once you have retrieved the flash codes, use the following list to understand the potential issues your Nissan is reporting:
- 11: Crank Angle Sensor/Camshaft Position Sensor.
- 12: Air Flow Meter/Mass Air Flow Sensor.
- 13: Engine Coolant Temperature Sensor.
- 14: Vehicle Speed Sensor.
- 21: Ignition Signal.
- 22: Fuel Pump.
- 23: Idle Switch.
- 24: Throttle Valve Switch.
- 25: Idle Speed Control Valve.
- 28: Cooling Fan Circuit.
- 31: ECM (Engine Control Module).
- 32: EGR Function.
- 33: Heated Oxygen Sensor.
- 34: Knock Sensor.
- 35: Exhaust Gas Temperature Sensor.
- 36: EGR Control-Back Pressure Transducer.
- 37: Knock Sensor.
- 38: Right hand bank Closed Loop (B2).
- 41: Intake Air Temperature Sensor.
- 42: Fuel Temperature Sensor.
- 43: Throttle Position Sensor.
- 44: ECCS Normal Operation (No Malfunction).
- 45: Injector Leak.
- 47: Crankshaft Position Sensor.
- 51: Injector Circuit.
- 53: Oxygen Sensor.
- 54: A/T Control (Automatic Transmission Control).
- 55: No Malfunction.
- 63: No. 6 Cylinder Misfire.
- 64: No. 5 Cylinder Misfire.
- 65: No. 4 Cylinder Misfire.
- 66: No. 3 Cylinder Misfire.
- 67: No. 2 Cylinder Misfire.
- 68: No. 1 Cylinder Misfire.
- 71: Random Misfire.
- 72: TWC Function right hand bank (Three-Way Catalytic Converter).
- 73: TWC Function right hand bank.
- 76: Fuel Injection System Function right hand bank.
- 77: Rear Heated Oxygen Sensor Circuit.
- 82: Crankshaft Position Sensor.
- 84: A/T Diagnosis Communication Line.
- 85: VTC Solenoid Valve Circuit (Variable Timing Control).
- 86: Fuel Injection System Function right hand bank.
- 87: Canister Control Solenoid Valve Circuit.
- 91: Front Heated Oxygen Sensor Heater Circuit right hand bank.
- 94: TCC Solenoid Valve (Torque Converter Clutch).
- 95: Crankshaft Position Sensor.
- 98: Engine Coolant Temperature Sensor.
- 101: Front Heated Oxygen Sensor Heater Circuit right hand bank.
- 103: Park/Neutral Position Switch Circuit.
- 105: EGR and EGR Canister Control Solenoid Valve Circuit.
- 108: Canister Purge Control Valve Circuit
ECU Diagnostic Mode Procedures (Modes I – V)
Beyond retrieving stored fault codes, these Nissan ECUs offer several diagnostic modes for real-time monitoring and component testing. To access these modes, you’ll use the same diagnostic selector switch.
Mode I – Exhaust Oxygen Sensor Monitor:
This mode allows you to check the functionality of your oxygen sensor.
- Warm the engine to its normal operating temperature.
- Run the engine at or above 2000 RPM without any load.
- Observe the GREEN LED on the ECU. It should blink ON and OFF more than five times within a 10-second period.
- If the green LED flashes fewer than five times, the oxygen sensor may need replacement. If it doesn’t flash at all, inspect the sensor’s wiring circuit.
Mode II – Mixture Ratio Control Monitor:
Mode II helps determine if the air/fuel mixture is cycling correctly.
- Ensure the engine is at normal operating temperature.
- Turn the diagnostic dial on the ECU fully clockwise (or switch to “ON” if equipped).
- After the LEDs flash twice, turn the dial fully counter-clockwise (or switch to “OFF”).
- Run the engine above 2000 RPM under no load.
- Observe the RED LED. If it blinks simultaneously with the GREEN LED, the air/fuel mixture is cycling correctly.
- If the RED LED remains OFF, the mixture is likely more than 5% rich.
- If the RED LED stays ON, the mixture is likely more than 5% lean.
- If the RED LED remains consistently ON or OFF above 2000 RPM, complete the full diagnostic procedures before undertaking any repairs.
Mode III – Stored Fault Code Reporting:
This is the mode you used earlier to retrieve stored trouble codes, as detailed in the procedures above.
Mode IV – Switch Operation Monitor:
Mode IV is used to verify the proper operation of the Throttle Position Sensor (TPS), Starter circuit, and Vehicle Speed Sensor (VSS).
- Turn the ignition switch to the “ON” position (engine off).
- Turn the diagnostic dial fully clockwise. After the LEDs flash four times, turn it fully counter-clockwise.
- Ensure the RED LED is initially OFF.
- Depress the gas pedal fully. The RED LED should turn ON. If not, inspect or replace the Throttle Position Sensor.
- Turn the ignition key to the “START” position (briefly engage the starter). The RED LED should turn ON. If not, check or replace the starter.
- Carefully drive the vehicle with the ECU exposed and visible (ensure it is safely secured). At speeds above 12 MPH, the GREEN LED should turn ON. If not, check or replace the Vehicle Speed Sensor.
Mode V – Real Time Diagnostic Function:
Mode V allows real-time monitoring of the Crankshaft Position Sensor (CPS), Mass Air Flow Sensor (MAFS), and Ignition signal.
- Start the engine.
- Turn the diagnostic dial fully clockwise. After the LEDs flash five times, turn it fully counter-clockwise.
- Observe the LEDs for 5 minutes while idling and revving the engine. Ideally, no LEDs should flash during this period.
- If LEDs flash, count the flashes, turn off the engine, and consult the following paragraphs for specific component checks. If no LEDs flash after 5 minutes, turn off the engine.
Real-time Diagnosis – Troubleshooting Guide (Mode V Flashes):
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RED LED flashes 3 times for 1.5 seconds: Indicates a potential issue with the Crankshaft Position Sensor. Check the CPS harness for continuity when the engine is off. Inspect the harness for dirt or damage and clean if necessary. Check the ECU pin terminals for bends and correct them. Reconnect the harness and re-test continuity. During real-time diagnosis, gently tap the harness connector or CPS component and observe if the trouble code reappears. If so, terminal replacement might be necessary.
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GREEN LED flashes 2-3 times for 0.5 seconds: Suggests a possible problem with the Mass Air Flow Sensor. Follow the same harness and terminal inspection and testing procedures as described for the CPS, but focus on the MAFS and its connections.
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GREEN LED flashes 4 times for 0.2 seconds: Points to a potential issue with the ignition signal. Again, use the same harness and terminal inspection and continuity testing methods, focusing on the ignition system wiring and connections.
By understanding and utilizing these ECU diagnostic procedures, you can effectively troubleshoot many common issues on your 1987-1995 Nissan Pathfinder or Hardbody pickup without relying on an OBD2 adapter. This direct ECU access provides invaluable insights into your vehicle’s health, empowering you to perform necessary maintenance and repairs, keeping your Nissan running reliably for years to come.
