Infiniti Q45 1990 - 1990 ENGINE PERFORMANCE Self-Diagnostics - Q45

Infiniti Q45 1990 - INTRODUCTION

If no faults were found while performing BASIC TESTING , proceed with ENTERING SELF-DIAGNOSTICS. If no fault codes or only pass codes are present, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).

Infiniti Q45 1990 - SELF-DIAGNOSTIC SYSTEM

The self-diagnostic system is used for diagnosing malfunctions of Electronic Concentrated Control System (ECCS) sensors and actuators. The Electronic Control Unit (ECU) has 2 available diagnostic modes. Before entering self-diagnostics, perform BASIC TESTING . This eliminates wasted diagnostic time and invalid diagnostic results.

NOTE:

When performing BASIC TESTING , be careful not to erase any diagnostic information stored in ECU memory.

Infiniti Q45 1990 - HARD FAILURES

Hard failures will cause CHECK ENGINE light to illuminate and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.

Infiniti Q45 1990 - INTERMITTENT FAILURES

Intermittent failures may cause CHECK ENGINE light to flicker or illuminate and go out after the intermittent fault goes away. However, the corresponding trouble code will be stored in ECU memory. Not all trouble codes will illuminate CHECK ENGINE light. If related fault does not reoccur within a certain time frame, related trouble code will be erased from ECU memory. Intermittent failures may be caused by a sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article.

NOTE:

Follow proper diagnostic routine when diagnosing the system. See DIAGNOSTIC ROUTINE table.

Infiniti Q45 1990 DIAGNOSTIC ROUTINE

Procedure

Order

Basic Diagnostic Procedures

1st

Entering Diagnostics

2nd

Retrieving Trouble Codes

3rd

Symptoms ⁽¹⁾

4th

Intermittents ⁽¹⁾

5th

⁽¹⁾	Symptoms and intermittents are covered in TESTS W/O CODES article.

Infiniti Q45 1990 - CHECK ENGINE LIGHT

NOTE:

All trouble codes do not activate CHECK ENGINE LIGHT.

All models are equipped with a CHECK ENGINE light. As a bulb check, light will illuminate when the ignition is turned on and engine is not running.

On California models, CHECK ENGINE light illuminates when a fault is detected with engine running. A corresponding trouble code will set in ECU memory. CHECK ENGINE light also illuminates if ECU or crank angle sensor malfunctions.

On Federal models, CHECK ENGINE light illuminates only when ECU or crank angle sensor malfunctions with engine running.

Infiniti Q45 1990 - DIAGNOSTIC MODES

The self-diagnostic system can detect ECCS malfunctions and store related trouble code. Intermittent codes are also stored. All codes are stored until cleared from memory. If an intermittent does not reoccur within 50 ignition key cycles, it will be cleared from memory.

Switching modes is not possible when the engine is running. During diagnosis, the self-diagnostic system will automatically return to Mode I from Mode II when the ignition switch is turned off.

Infiniti Q45 1990 - MODE I

This is normal operating mode. In this mode, the CHECK ENGINE light and Red Light Emitting Diode (LED) inspection light in ECU stay on when the ignition is turned on, engine off (bulb check). If the engine is started, CHECK ENGINE light and Red LED in ECU should turn off, unless a fault or trouble code is present (Calif. models) or if the ECU or crank angle sensor is malfunctioning (Calif. and Fed. models).

Infiniti Q45 1990 - MODE II

This is self-diagnostic mode for retrieving fault or trouble code(s). See RETRIEVING CODES. With the engine running, Mode II can monitor air/fuel mixture feedback control. The CHECK ENGINE light and Red LED in the ECU will flash on (lean) and off (rich) more than 5 times every 10 seconds with engine speed at 2000 RPM when system is in closed loop. The CHECK ENGINE light and Red LED do not flash remain on or off if system is in open loop.

Infiniti Q45 1990 - ECU LOCATION

The ECU is located behind the right kick panel.

Infiniti Q45 1990 - ENTERING SELF-DIAGNOSTICS

Turn ignition switch to ON position, engine off. Using a small screwdriver, turn diagnostic mode selector on ECU fully clockwise. Wait at least 2 seconds and then turn diagnostic mode selector fully counterclockwise. Mode II self-diagnostic will result and the CHECK ENGINE light and the Red LED inspection light will flash trouble codes (if present).
If engine is started at this stage, the CHECK ENGINE light and the Red LED inspection light will display the condition of the air/fuel mixture which is monitored by the O2 sensor or if the system is in closed or open loop.

Infiniti Q45 1990 - RETRIEVING CODES

NOTE:

Mode II can retrieve trouble code(s) from self-diagnostic system.

Read trouble codes with either CHECK ENGINE light or Red LED inspection light on ECU. Trouble codes will flash after selecting Mode II.

Trouble codes are indicated by the number of flashes from CHECK ENGINE light or Red LED inspection light. Count the flashes. For example, 3 long (.6 second) flashes followed by 2 short (.3 second) flashes of CHECK ENGINE light or Red LED indicate a Code 32.

Infiniti Q45 1990 TROUBLE CODE IDENTIFICATION CHART

Code

System Affected

Probable Cause

11 ⁽¹⁾ ⁽²⁾

Crank Angle Sensor (Q45)

No crank signal

Airflow Meter Circuit

Open/shorted circuit

Coolant Temp. Sensor

Open/shorted circuit

Vehicle Speed Sensor (VSS)

No VSS signal

21 ⁽¹⁾ ⁽²⁾

Ign. Signal Circuit (Q45)

Open/shorted circuit

ECU

Signals not normal

EGR Function (Calif.)

No EGR action

O2 Sensor (Left Bank-Q45)

Open ckt/high O2 signal

34 ⁽¹⁾

Knock Sensor (Q45)

Open/shorted ckt

EGR Temp. Sensor (Calif.)

Open/shorted ckt

Throttle Sensor

Open/shorted ckt

Injector Leak (Calif.)

Leak at injector(s)

Injector Circuit (Calif.)

Injector doesn't work

O2 Sensor (Right Bank-Q45)

Open ckt/high O2 signal

54 ⁽¹⁾

Auto. Trans. Signal (Q45)

Open signal transmission control unit

55 ⁽¹⁾

No Malfunction (Q45)

Normal condition

⁽¹⁾	These trouble code(s) not will activate CHECK ENGINE light.

⁽²⁾	Check items causing a malfunction of crank angle sensor circuit first, if Codes 11 and 21 are present at same time.

Infiniti Q45 1990 - CLEARING CODES

NOTE:

Ensure all diagnostic codes are accessed from ECU memory before disconnecting battery or switching from Mode II to Mode I.

Infiniti Q45 1990 - MEMORY ERASE

Stored memory can be erased by disconnecting battery or selecting Mode I after Mode II has been accessed.

Infiniti Q45 1990 - SUMMARY

If no hard fault codes (or only pass codes) are present, proceed to TESTS W/O CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.) or intermittent diagnosis procedures.