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

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

Do you have a check engine light on in your D21/WD21 generation Nissan Pathfinder or Hardbody? Need to know how to Read ECU codes on your Nissan? If you so you came to the right place!

Read ECU codes Nissan Pathfinder

The stock ECU location is under the passenger side seat. You can get to two different ways, by sliding the seat all the way forward and removing the plastic cover. Or you can remove the seat which can make access a little easier.

Nissan Pathfinder ECU location under Passenger Seat

If you have a VG30i (1986-1989) then the ECU has a tiny toggle switch on the side to select diagnostic mode.

picture of vg30i switch

The 4-cylinder engines (the Z24i and KA24E) and the VG30E ECU have a slotted switch on the side that turns 1/4 or 1/2 turn clockwise and counterclockwise to turn on and off. Because Nissan is a bit ridiculous you may find some early 4cyl Hardbody ECU’s to have the switch not the slot but it will be one or the other.

Test Procedure

For the Z24i and KA24E 4-cylinder engines:

Turn ignition switch to on, but don’t start the engine. Dash lights should come on.
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.
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)
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.
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:

Turn ignition switch on, but don’t start the engine. Dash lights should come on.
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.
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.
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.

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

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

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

41 – Intake Air Temperature Sensor

42 – Fuel Temperature Sensor

43 – Throttle Position Sensor

44 – ECCS Normal Operation

45 – Injector Leak

47 – Crankshaft Position Sensor

51 – Injector Circuit

53 – Oxygen Sensor

54 – A/T 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

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

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

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 codes Nissan Pathfinder Diagnostic Mode Procedures

Mode 1 – Exhaust Oxygen Sensor Monitor

Use Mode 1 to determine if the Oxygen Sensor is functioning properly.

Warm the engine to normal operating temps.
Run the engine above 2000 RPM under no load while looking at the ECU.
Make sure the GREEN LED goes on and off more than five times during ten seconds at 2000 RPM.
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

Use Mode 2 to determine if the air/fuel mixture is correct.

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

Mode 3 – Stored Fault Code Reporting

Use Mode 3 to retrieve all stored trouble codes in memory.

Use the above instructions.

Mode 4 – Switch Operation Monitor

Use Mode 4 to determine if the Throttle Position Sensor (TPS), Starter circuit and/or Vehicle Speed Sensor (VSS) are in proper working order.

Turn the ignition switch on, but do not start the engine.
Turn the dial on the ECU fully clockwise. After the LED flashes 4 times, turn the dial fully counter clockwise.
Make sure the RED LED is turned off.
Make sure the RED LED turns on when depressing the gas pedal. If not, check or replace the Throttle Position Sensor.
Make sure the RED LED turns on when turning the ignition key the START position. If not, check or replace the starter.
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

Use Mode 5 to determine if the Crankshaft Position Sensor (CPS), Mass Air Flow Sensor (MAFS) and/or Ignition signal are working properly.

Start engine.
Turn the dial on the ECU fully clockwise.
After the LED flashes 5 times, turn the dial fully counter clockwise.
Make sure LEDs do not flash for 5 minutes when racing or idling the engine.
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.
If LEDs do not flash for 5 minutes, turn engine off.

Mode 5 ECU Code Information

If the RED LED flashes 3 times for 1.5 seconds, check the Crankshaft Position Sensor. Check the harness continuity at CPS when the engine is stopped. Inspect the harness for dust and clean if necessary. Check the pin terminal at ECU for bends and remove them as necessary. Reconnect harness and recheck continuity. During real-time diagnosis, tap the harness connector or component and check if trouble code is displayed. If so, replace terminal.

If the GREEN LED flashes 2-3 times for 0.5 seconds, check Mass Air Flow Sensor. Check the harness continuity at MAFS when the engine is stopped. Inspect the harness for dust and clean if necessary. Check the pin terminal at ECU for bends and remove them as necessary. Reconnect harness and recheck continuity. During real-time diagnosis, tap the harness connector or component and check if trouble code is displayed. If so, replace terminal.

If the GREEN LED flashes 4 times for 0.2 seconds 3 times, check the ignition signal. Check the harness continuity when the engine is stopped. Inspect the harness for dust and clean if necessary. Check the pin terminal at ECU for bends and remove them as necessary. Reconnect harness and recheck continuity. During real-time diagnosis, tap the harness connector or component and check if trouble code is displayed. If so, replace terminal.

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