Nissan ECU Diagnosis Without CONSULT Tool

In this article we will be using a Z32 for basic ECU diagnosis to retrieve DTCs for pre-OBDII vehicles. Nissan offers CONSULT tests for a fee to pinpoint problems through the ECU. There are procedures to get some of the same results without a CONSULT tool from the ECU’s memory.

Skill Level 2 of 5

Time Required < 1hr.

Procedure

1. Remove the passenger floor mat.

2. Pull back carpet. It’s held up with 3 spots of velcro.

3. Remove the wooden floorboard (4 x 10 mm bolts)

4. The screw potentiometer is on the right side of the ECU, the coding LED is in the oval hole above it.

5. Turn the ignition switch on, but do not start the engine.

6. Turn ‘diagnostic mode selector’ (pot on side) fully clockwise. Wait at least 2 seconds, then turn pot fully counter clock-wise. The ECU is now in Diagnostics MODE II

7. Read the codes from the flashing LED on the side of the ECU (or the check engine light). Long flash is first digit, short flash is 2nd digit, the codes are at the bottom of this page.

8. To exit MODE II, turn pot fully clock-wise. Wait at least 2 seconds, then turn the potentiometer fully counter clock-wise, or…

9. Start engine with the ECU in MODE II to enter MODE II – Heated Oxygen Sensor (O2) Monitor . The ECU is now monitoring the left O2 sensor. Warm the engine to normal operating temperature, then run at 2000 rpm for 2 minutes. Check that the LED blinks (or the check engine light) more than 5 times every 10 seconds at 2000 rpm.

10. To change to right sensor turn the ECU potentiometer clockwise with engine still running, wait 2 seconds, turn it back. Check the lights at 2000 rpm again for a similar switching condition.

Note: Light indicates signal from sensor to ecu. ON=rich, Off=lean. Blinking light means system is constantly adjusting between lean and rich which is normal. Any other indication would be abnormal and require further investigation. The switched on/off is ‘closed loop’, while a constant on or off is ‘open loop’

11. To exit MODE II – Heated Oxygen Sensor Monitor, turn the potentiometer fully counter clock-wise and stop the engine.

LED codes for MODE II:

11: crank angle sensor circuit

12*: air flow meter circuit

13*: engine coolant temp. sensor circuit

14*: vehicle speed sensor circuit

21: ignition signal circuit

26*: boost pressure sensor

31*: ECU

32*: EGR function

33*: exhaust gas sensor circuit (left)

34: detonation sensor circuit

35*: exhaust gas temp. sensor circuit

42: fuel temp. sensor circuit

43*: throttle position sensor circuit

45*: injector leak

51*: injector circuit

53*: exhaust gas sensor circuit (right)

54: signal circuit from A/T control to ECU

55: NO malfunctions in the above

*Will cause the Check Engine light to come on under normal (MODE I) operating conditions.

This section includes the following:
Trouble Code Detected Items Malfunction Caused By Check

11* Camshaft Angle Sensor circuit (CAS) Either 1° or 120° signal is not entered for the first few seconds of engine cranking. Either 1° or 120° signal is not input often enough while the engine speed is higher then the specified RPM. Check harness and connector (if harness and connector are OK, CAS might be bad)

12 Mass Air-Flow Sensor circuit (MAS) The MAS sensor circuit is open or shorted (abnormally high or low voltage is registered). Check harness and connector (if harness and connector are OK, MAS might be bad)

13 Engine Coolant Temp. Sensor The Engine Coolant Temp. Sensor circuit is open or shorted (abnormally high or low voltage is registered). Check harness and connector, Engine Coolant Temp. Sensor

14 Speed Sensor circuit The Speed Sensor circuit is open or shorted. Check harness and connector; Speed Sensor switch (reed switch)

21* Ignition signal circuit The ignition signal in the primary circuit is not entered during engine cranking or running. Check harness and connector; Power Transistor Unit

26 Boost Pressure sensor (Turbo models) The boost pressure sensor is open or shorted (abnormally high or low voltage is registered). Check harness and connector; Boost pressure leaks; Boost pressure sensor

31 ECU ECU calculation function is failing. Replace ECU

32 EGR function EGR valve does not operate (valve spring does not lift). Check EGR valve; EGRC-solenoid valve

33 O2 Sensor (left side) The O2 Sensor is open or shorted (abnormally high or low voltage is registered). Check harness and connector; O2 sensor; Fuel pressure; Injectors; Intake air leaks

34 Detonation Sensor circuit The detonation sensor circuit is open or shorted (abnormally high or low voltage is registered). Check harness and connector; Detonation sensor

35 EGR Temp. Sensor The EGR Temp. Sensor circuit is open or shorted (abnormally high or low voltage is registered). Check harness and connector; EGR temp. sensor

42 Fuel Temp Sensor circuit The Fuel Temp. Sensor circuit is open or shorted (abnormally high or low voltage is registered). Check harness and connector; Fuel temp. sensor

43 Throttle Position Sensor circuit The Throttle Position Sensor circuit is open or shorted (abnormally high or low voltage is registered). Check harness and connector; Throttle position sensor

45 Injector leak Fuel leaks from the injectors. Check injectors

51 Injector circuit The injector circuit is open. Check harness and connector; Injectors

53 O2 Sensor (right side) The O2 Sensor is open or shorted (abnormally high or low voltage is registered). Check harness and connector; O2 sensor; Fuel pressure; Injectors; Intake air leaks

54 Signal circuit from the automatic transmission (A/T) (A/T models only) The A/T communication line is open or shorted. Check harness and connector

* Check items causing a malfunction of the CAS circuit first if both diagnostic codes 11 & 21 are displayed at the same time.