How to Read Nissan ECU Codes (1987-1995 Pathfinder & Hardbody)

How to read ECU codes from 1987-1995 WD21 Nissan Pathfinder and D21 Hardbody

Having trouble pulling ECU codes for your Nissan Pathfinder or Hardbody? Below is a step-by-step guide on how to retrieve diagnostic trouble codes or DTC without needing a scan tool. Whether you’re diagnosing a check engine light or troubleshooting issues, this guide will help.

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Read ECU codes Nissan Pathfinder

Test Procedure

For the Z24i and KA24E 4-cylinder engines:

1. Turn ignition switch to on, but don’t start the engine. Dash lights should come on.
2. Twist the ‘Diagnostic Mode Selector’ screw on the ECU all the way clockwise. The check engine light should turn off. Wait 5 seconds, then turn the screw all the way back counter clockwise.
3. The Check Engine light on the dash will begin to flash the trouble code. (The amount of long flashes is the 1st digit, the of short flashes is the 2nd digit)
4. To clear all the stored codes and turn the check engine light off, turn the screw all the way clockwise while in diagnostic mode, wait 5 seconds, then turn the screw back all the way counter clockwise.
5. To save the stored codes, simply turn the key off while the check engine light is flashing. The ECU will  save codes and the check engine light will remain on.

For the VG30i and VG30E V-6 engines:

1. 1. Turn ignition switch on, but don’t start the engine. Dash lights should come on.
   2. VG30i: There is a little plastic tab holding the switch on the ECU. Remove the tab and behind it you will find a small toggle switch with 2 positions, “ON” and “DIAGNOSTICS”. Using a small flathead screwdriver, flip it to the diagnostics position. The red and green LED’s on top of the ECU will start blinking. One blink, pause, two blinks, pause, three blinks, pause…etc for each of the 5 modes. Mode 3 is typically the place to start as it will give you the error codes stored in the ECU and you can check them in the chart below.
   3. VG30E: Turn the ‘diagnostic mode selector’ screw on the side of the ECU all the way clockwise. The check engine light will turn off, wait 5 seconds, then turn the screw all the way back counter clockwise. The LED’s on the ECU begin blinking the modes as I explained above. Typically if you want to pull the codes you’re looking for mode 3 so wait until the LEDs blink 3 times move the toggle switch back to the On position. After about five seconds it will start to blink the diagnostic codes on the ECU. Note each code as it is displayed, the red LED flashing for 10’s column, and the green LED flashing for for 1’s column. Example: Seven red flashes and six green flashes means code 76: Fuel Injection System Function Right Hand Side.

1. To clear the ECU of any stored codes turn the switch to the “DIAGNOSTICS” position and then back to the “ON” position and turn off the key.

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1986.5-1995 Nissan ODB1 ECU Flash Codes for all engines:

ECU codes Nissan Pathfinder Diagnostic Mode Procedures

Mode 1 – Exhaust Oxygen Sensor Monitor

1. Warm the engine to normal operating temps.
2. Run the engine above 2000 RPM under no load while looking at the ECU.
3. Make sure the GREEN LED goes on and off more than five times during ten seconds at 2000 RPM.
4. If the number of flashes are less than five, replace the oxygen sensor. If the LED does not flash, check the sensor’s circuit.

Mode 2 – Mixture Ratio Control Monitor

1. Warm the engine to normal operating temps.
2. Turn the dial on the ECU fully clockwise (or if you have a switch, turn it on).
3. After the LED flashes twice, turn the dial fully counter clockwise (or turn the switch off).
4. Run the engine above 2000 RPM under no load while looking at the ECU.
5. If the RED LED blinks simultaneously with the GREEN LED, the air/fuel mixture is cycling properly.
6. If the RED LED stays off, the mixture is more than 5% rich.
7. If the RED LED stays on, the mixture is more than 5% lean.
8. If the RED LED stays on or off above 2000 RPM, complete the diagnostics before beginning repairs.

Mode 3 – Stored Fault Code Reporting

Mode 4 – Switch Operation Monitor

1. Turn the ignition switch on, but do not start the engine.
2. Turn the dial on the ECU fully clockwise. After the LED flashes 4 times, turn the dial fully counter clockwise.
3. Make sure the RED LED is turned off.
4. Make sure the RED LED turns on when depressing the gas pedal. If not, check or replace the Throttle Position Sensor.
5. Make sure the RED LED turns on when turning the ignition key the START position. If not, check or replace the starter.
6. Drive the vehicle with the ECU unbolted and within view. Make sure the GREEN LED turns on when speed is 12 MPH or more. If not, check or replace the Vehicle Speed Sensor.

Mode 5 – Real Time Diagnostic Function

1. Start engine.
2. Turn the dial on the ECU fully clockwise.
3. After the LED flashes 5 times, turn the dial fully counter clockwise.
4. Make sure LEDs do not flash for 5 minutes when racing or idling the engine.
5. If it flashes, count the number of flashes, turn engine off, and see the following 3 paragraphs. Perform real-time diagnosis inspection and repair or replace malfunctioning part if present.
6. If LEDs do not flash for 5 minutes, turn engine off.

Mode 5 ECU Code Information

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