Engine Controls - Self-Diagnostics - Introduction - G20 & Q45: Other Infiniti G20 II

OBD-II

ECM detects malfunctions related to engine sensors or actuators. OBD-II monitors emission related components and can store Diagnostic Trouble Codes (DTCs), 1st trip DTCs, freeze-frame data, 1st trip freeze-frame data and System Readiness Test (SRT) information. Using a scan tool, this data and DTC information can be retrieved to assist in diagnosing problems. On Q45, the Malfunction Indicator Light (MIL) can be used for code retrieval and fuel feedback monitoring.

When a malfunction is detected for the first time, the 1st trip DTC and 1st trip freeze frame data are stored in Engine Control Module (ECM) memory. However, in most instances, MIL will not be illuminated. If the same malfunction is detected on the next trip (under similar conditions), MIL will be illuminated and a DTC is stored (2nd trip detection logic). If a misfire or fuel system malfunction should occur during 1st trip, MIL may be illuminated or flash. DTC and freeze-frame information will be stored to aid in diagnostics by specifying operating conditions when DTC was set.

FREEZE-FRAME DATA

Note. 1st trip freeze-frame data values can only be displayed with Nissan's CONSULT, and are not displayed on generic scan tool.

ECM records operating conditions such as fuel system status, calculated load value, engine coolant temperature, short term fuel trim, long term fuel trim, engine speed, vehicle speed and absolute pressure. Freeze-frame data is a "snapshot" of these operating conditions present when a fault is detected. When a fault is detected for the first time, ECM stores the first trip DTC, along with first trip freeze-frame data. Only one set of freeze-frame data can be stored in ECM (either first trip freeze-frame data or freeze-frame data). There is no priority for first trip freeze frame data. It is updated each time a different first trip DTC is stored. If a fault is detected for the second time, first trip freeze-frame data is replaced with freeze-frame data.

Freeze-frame data is updated in order of priority. See FREEZE FRAME PRIORITY IDENTIFICATION table. If a priority 1 fault (misfire or fuel injection system malfunction) is detected in another trip when priority 2 freeze-frame data is already stored in ECM, priority 2 freeze-frame data will be replaced by priority 1 freeze-frame data.

Note. Only one 1st trip DTC and one freeze-frame data "snapshot" can be stored in ECM. If using a generic scan tool, 1st trip DTC freeze-frame information may not be accessible. Use CONSULT to retrieve 1st trip DTC freeze-frame information.

FREEZE FRAME PRIORITY IDENTIFICATION

MIL Code Display

MIL Code is a 4 digit number indicated by 2 separate 2 digit numbers flashed by MIL. The 2 separate numbers are separated by a pause (.9 second). The first number will be long flashes (.6 second), and the second will be short flashes (.3 second). If there is more than one MIL DTC stored, there will be a 2.1-second pause between codes.

For example, 3 long (.6 second) flashes, a pause (.9 second), then followed by 3 short (.3 second) flashes of MIL indicate a MIL Code 0303. If 2 different MIL Codes are stored, such as 0406 and 0608, this would be displayed by 4 long flashes, pause, 6 short flashes, long pause, 6 long flashes, pause, 8 short flashes of MIL.

Erasing Stored Information

Note. Test modes cannot be switched with engine running. When ignition is turned off, power to ECM will turn off after 5 seconds. ECM will then return to diagnostic test mode I. Ensure test mode selector is in fully counterclockwise position when vehicle is in use.

The following emission related information will be erased from ECM memory: DTCs stored, 1st trip DTCs, freeze frame data, 1st trip freeze frame data, System Readiness Test (SRT) codes and test values. To erase this information, switch from diagnostic test mode II to diagnostic test mode I. While ECM is in diagnostic test mode II, turn mode selector on ECM fully clockwise, wait 2 seconds and turn mode selector fully counterclockwise.

Mode 2: Freeze Frame Data

This mode gains access to emission-related data value information stored by ECM during the freeze frame portion of self-diagnostic mode during engine operation.

Mode 4: Clearing Codes

This mode can clear all emission related diagnostic information for DTCs. These include

1. Clear number of DTCs (MODE 1).
2. Clear DTCs (MODE 3).
3. Clear DTC for freeze-frame data (MODE 1).
4. Clear freeze-frame data (MODE 2).
5. Reset status of system monitoring test (MODE 1).
6. Clear on-board monitoring results (MODE 6 and 7).

Mode 6: On-Board Tests

This mode accesses the results of on-board diagnostic monitoring tests of specific components and systems that are not continuously monitored.

Mode 7: On-Board Tests

This mode enables the on board test drive to obtain test results for emission-related powertrain components and systems that are continuously monitored during normal driving conditions.

INTERMITTENT SIMULATION TESTS

Consider the following conditions to recreate an intermittent malfunction

1. Drive vehicle on rough road or with engine vibrating at idle (with A/C on).
2. Incident occurs on only extremely hot or cold days.
3. Water may intrude into connectors and cause corrosion between connector terminals.
4. Operate multiple accessories (P/W, P/L, A/C, wipers, lights, etc.).
5. Start vehicle either hot or cold.
6. Wiring harnesses may be checked by gently wiggling wire harness during testing. Relays and sensors may be checked by gently tapping during testing.

Using MIL (Q45 Only)

Turn ignition off. Wait 5 seconds. Turn ignition on. Perform MIL diagnostics for stored DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES USING MIL . Change diagnostic test mode selector switch on ECM from mode II to mode I.

FAIL-SAFE MODES

ECM enters a fail-safe mode if certain malfunctions are detected due to an open or short circuit. When ECM enters fail-safe mode, MIL illuminates. Refer to all diagnostic tests that apply for description and testing of circuit affected.

ECM (DTCs Not Accessible)

Maximum engine speed is 3000 RPM. Fuel injection operates in simultaneous mode. Ignition timing is fixed. Fuel pump relay remains on when engine is running and off when engine stalls. IACV-AAC valve is fully open (except Q45). Cooling fans remain on at high speed when engine is running and turn off when engine stalls (except G20).

FUEL FEEDBACK MONITORING USING MIL - Q45 ONLY

1. Enter Mode II diagnostics using MIL. See «RETRIEVING DIAGNOSTIC TROUBLE CODES USING MIL»(ref-3085-S26777903642000041700000) under SELF-DIAGNOSTIC SYSTEM. If engine is started at this stage, MIL will display condition of air/fuel mixture, monitored by the front Heated Oxygen Sensors (HO2S), whether the vehicle is in closed loop or open loop. With engine at normal operating temperature, run engine at about 2000 RPM for 2 minutes under no-load condition. MIL should flash 5 times every 10 seconds indicating normal operating condition of air/fuel mixture monitored by front HO2S(s).
2. When MIL is on, it indicates a lean condition. When MIL is off, it indicates a rich condition. MIL switching on and off indicates closed loop operation. If MIL remains on or off, it indicates an open loop condition.
3. To switch to opposing HO2S, turn diagnostic test mode selector on ECM fully clockwise, wait 2 seconds and turn mode selector fully counterclockwise. MIL will now indicate changing to opposing HO2S by rapidly flashing and returning to lean/rich cycling. HO2S feedback of the opposing bank HO2S will now be displayed by MIL.
4. Repeat step 3 to switch back to original HO2S feedback signal. Switch from bank to bank as necessary. To erase stored DTC information, go to «ERASING STORED INFORMATION»(ref-3085-S17302094812000041700000) under SELF-DIAGNOSTIC SYSTEM. To remain in Mode II, turn engine off and immediately turn ignition on.

Checking SRT Code Status

Select MODE 1 with scan tool, and observe SRT STATUS. An INCMP display for any SRT system indicates the self-diagnosis for that circuit is incomplete. SRT systems that have completed self-diagnosis will be indicated by CMPLT, indicating SRT is set. If any category is incomplete, go to SETTING SRT CODES .

Setting SRT Codes

To set all SRT codes as complete, drive vehicle according to procedure shown in illustration. (Scheme 4) Perform driving procedure one or more times. If driving procedure is interrupted, repeat procedure. On A/T models, operate vehicle with shift lever in "D" position and overdrive turned on. On M/T models, shift gears at suggested speeds. See SUGGESTED SHIFT SPEEDS (M/T) table. DO NOT exceed maximum suggested speed in any gear. See MAXIMUM SPEED FOR EACH GEAR table.

Scheme 4

SUGGESTED SHIFT SPEEDS (M/T)

MAXIMUM SPEED FOR EACH GEAR

SUMMARY

If no DTCs (or only pass codes) are present and driveability symptoms exist, or intermittent codes exist, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.