Engine Controls Self-Diagnostics - Introduction: Diagnosis Nissan Altima L30

DIAGNOSTIC TROUBLE CODES (DTCs)

The Engine Control Module (PCM) monitors several different engine control circuits. If a malfunction occurs, PCM will record a Diagnostic Trouble Code (DTC). The next time engine is started and the same malfunction is detected PCM will turn on MIL, signaling a DTC is in PCM memory.

After 3 consecutive drive cycles without a malfunction, PCM will turn off MIL, however DTC will be stored in PCM memory. If PCM does not detect that fault for 40 drive cycles, DTC will be cleared from PCM memory. PCM will clear a DTC for a misfire or fuel trim malfunction when fault is not detected for 80 drive cycles with engine speed, coolant temperature, etc. similar to when malfunction first occurred.

Hard faults cause MIL to illuminate and remain on until the malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined. If a sensor fails, PCM will use a substitute value in its calculations to continue engine operation. See FAIL-SAFE MODE under SELF-DIAGNOSTICS SYSTEM. In this condition, vehicle is functional, but driveability will be affected.

Diagnostic Test Mode I

As a bulb check, light glows when ignition is turned on and engine is not running. When vehicle is started, MIL will turn off, indicating that no malfunctions are detected. If a malfunction is detected while the engine is running, the MIL glows or flashes and a corresponding DTC will be set in PCM memory.

Diagnostic Test Mode II

Turn ignition on, but leave engine off. Using a small screwdriver, turn diagnostic mode selector on PCM fully clockwise and MIL should turn off. Wait at least 2 seconds, and then turn diagnostic mode selector fully counterclockwise which will enter into diagnostic test mode II. MIL will flash any DTC(s) present. If 2 or more DTCs are displayed, they may be DTC's or 1st trip DTCs. These can be identified by using CONSULT or GST. To erase stored diagnostic information, see ERASING STORED INFORMATION.

Mode 1: Readiness Test

This mode accesses current emission related data input and output values. In this mode, system status information is also monitored.

Mode 3: Diagnostic Trouble Codes (DTCs)

This is self-diagnostic mode for retrieving emission-related and powertrain DTCs stored in PCM memory.

Mode 8: EVAP System Testing

This mode can close or open EVAP system components, with ignition switch in the "ON" position, the following components can be opened or closed

1. EVAP canister vent control can be opened
2. Vacuum cut valve by-pass valve can be closed.

During the following conditions, mode 8 cannot function

1. Low ambient temperature or low fuel temperature.
2. Low battery voltage.
3. Engine running or ignition switch in the "OFF" position.
4. Too much pressure applied to EVAP system.

VISUAL INSPECTION

Before proceeding with self-diagnostics, visually check the following and prepare vehicle as follows

1. Perform all necessary safety precautions to prevent personal injury or vehicle damage.
2. Block drive wheels. Set parking brake. Place shift lever in Park (A/T) or Neutral (M/T). DO NOT move shift lever during test unless specifically directed to do so.
3. Check condition of air cleaner and air ducting.
4. Check all vacuum hoses for leaks, restrictions and proper routing.
5. Check EEC system wiring harness connections for corrosion, damaged pins, loose wires and improper routing.
6. Check PCM, sensors and actuators for physical damage.
7. Check engine coolant and oil level.
8. Check battery condition.
9. Check exhaust system for leaks.
10. Turn off all lights and accessories. Ensure vehicle doors are closed when measuring voltage.

ENTERING SELF-DIAGNOSTICS

There are several methods available to enter into self-diagnostics. Using either Nissan's CONSULT, a Generic Scan Tool (GST) or Malfunction Indicator Light (MIL) self-diagnostics may be used to enter and access stored Diagnostic Trouble Codes (DTCs). If using CONSULT, follow screen prompts. If not using CONSULT, see WITHOUT SCAN TOOL (EXCEPT QUEST) or WITHOUT SCAN TOOL (QUEST) under RETRIEVING CODES.

Using Scan Tool

1. Ensure engine is warmed to normal operating temperature. If engine does not start, continue with testing. Turn ignition on. Ensure test equipment is properly attached.
2. Using the scan tool, select and enter the following data: Select vehicle and engine selection menu. Select year, engine, model and any additional information requested by scan tool. Select PCM. Select DTCs. Select DIAGNOSTIC TEST MODE RESULTS.
3. At this point, scan tool should display all DTCs. Write down codes in order displayed. If a communication problem exists between scan tool and PCM, check for loose power and data cables to scan tool.

Note. Before switching MIL to Mode 2, perform bulb check (key on engine off). If MIL is inoperative, check and repair MIL circuit as necessary.

Note. DTCs retrieved by MIL may also be referred to as flash codes.

Without Scan Tool (Except Quest)

1. If use of an OBD-II type scan tool is not available, DTCs can be retrieved by changing PCM output from Mode 1 to Mode 2. Mode 1 is the normal malfunction warning mode. Mode 2 displays self-diagnostic results.
2. To switch PCM output from Mode 1 to Mode 2, locate and gain access to PCM. See «PCM LOCATIONS»(ref-18070-S38013919292000122900000) table. Turn ignition on. Using a screwdriver, turn test mode selector fully clockwise. (Scheme 1) After 2 seconds, turn test mode selector fully counterclockwise (back to original position). PCM should now be in Mode 2. When in Mode 2 with key on and engine off, MIL should begin flashing codes. PCM LOCATIONS Application Location Altima, Sentra, 200SX Under Dash, Behind Center Console Maxima Behind Glove Box Pathfinder, QX4 & Frontier Under Passenger Seat Quest Behind Glove Box 240SX At Kick Panel Under Right Side Of Dash
3. The 4-digit DTCs (flash codes) are read as two 2-digit numbers. The first 2-digit number is indicated by a series of long flashes followed by a series of short flashes. For example: one long flash followed by 2 short flashes indicates DTC 0102. (Scheme 2) The DTCs retrieved by MIL are not numerically the same as DTCs retrieved from a scan tool. See appropriate DTC IDENTIFICATION table under «SUMMARY»(ref-18070-S27018664872000122900000).
4. Write down codes and repair in order of priority. See «DTC PRIORITY IDENTIFICATION»(ref-18070-S34527690762000122900000) table. To determine which circuit test to use, see appropriate DTC IDENTIFICATION table under «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-18070-S37497302092003082500000). After retrieving DTCs or performing a repair, clear DTCs from PCM memory. See «CLEARING CODES»(ref-18070-S18556901412000122900000). If no DTCs or DTC P0000/MIL 0505 (pass code) were retrieved and fault still exists, proceed to «TESTS W/O CODES»(ref-18078) article for diagnosis by symptom.

Without Scan Tool (Quest)

1. If use of an OBD-II type scan tool is not available, DTCs can be retrieved by changing PCM output from Mode 1 to Mode 2. Mode 1 is the normal malfunction warning mode. Mode 2 displays self-diagnostic results.
2. To switch PCM output from Mode 1 to Mode 2, locate the self-test harness connector. (Scheme 3) Turn ignition on. Disconnect self-test harness connector and jump terminals No. 3 and 6 together. Disconnect jumper wire after being connected for at least 2 seconds. Reconnect self-test connector. MIL should now be in Mode 2. When in Mode 2 with engine off, MIL should begin flashing codes.
3. The 4-digit DTCs (flash codes) are read as two 2-digit numbers. The first 2-digit number is indicated by a series of long flashes followed by a series of short flashes. E.g. one long flash followed by 2 short flashes indicates DTC 0102. (Scheme 2) The DTCs retrieved by MIL are not numerically the same as DTCs retrieved from a scan tool.
4. Write down DTCs and repair in order of priority. See «DTC PRIORITY IDENTIFICATION»(ref-18070-S34527690762000122900000) table. To determine which circuit test to use, see appropriate DTC IDENTIFICATION table under «SUMMARY»(ref-18070-S27018664872000122900000). After retrieving DTCs or performing a repair, clear DTCs from PCM memory. See «CLEARING CODES»(ref-18070-S18556901412000122900000). If no DTCs or DTC P0000/MIL 0505 (pass code) were retrieved and fault still exists, proceed to «TESTS W/O CODES»(ref-18078) article for diagnosis by symptom.

Scheme 1

Scheme 2

Scheme 3

TESTING PROCEDURE

To ensure correct diagnosis and repair, testing should be done in the following sequence

1. Ensure all customer complaints or observations are recorded. Test drive vehicle with customer when necessary for malfunction verification.
2. Retrieve and record stored DTCs and 1st trip DTCs. See «RETRIEVING CODES»(ref-18070-S01755559822000122900000) . Print or record freeze frame data and erase DTC(s). See «CLEARING CODES»(ref-18070-S18556901412000122900000) .
3. Recreate conditions in which malfunction occurred to reset DTC. If DTC is detected, go to step 5). If malfunction is not detected, consider the following conditions to recreate an intermittent malfunction: Vehicle Vibration Drive vehicle on rough road or with engine vibrating at idle (with A/C on). Heat Or Cold Sensitive Incident occurs on only extremely hot or cold days. Water Intrusion Water may intrude into connectors and cause corrosion between connector terminals. Electrical Load Operate multiple accessories (P/W, P/L, A/C, wipers, lights, etc.). Hot Or Cold Start Start vehicle either hot or cold. Poor Connections Wiring harnesses may be checked by gently wiggling wire harness during testing. Relays and sensors may be checked by gently tapping during testing. If malfunction is still not detected, go to next step. NOTE: Perform DTCs in order of priority. See «DTC PRIORITY IDENTIFICATION»(ref-18070-S34527690762000122900000) table.
4. Perform malfunction confirmation procedure (if available) at the beginning of each DTC diagnostic test to set appropriate DTC. See appropriate TESTS W/CODES article For Altima, see «TESTS W/CODES - TESTING»(ref-18071) For Frontier, see «TESTS W/CODES - TESTING»(ref-18074) For Maxima, see «TESTS W/CODES - TESTING»(ref-18072) For Pathfinder and Infiniti QX4, see «TESTS W/CODES - TESTING»(ref-18075) For Quest, see «TESTS W/CODES - TESTING»(ref-18076) For Sentra and 200SX, see «TESTS W/CODES - TESTING»(ref-18073) For 240SX, see «TESTS W/CODES - TESTING»(ref-18077) .
5. If DTC is set, perform appropriate procedure. If DTC does not reset, diagnose malfunction by symptom. See TESTS W/O CODES article for diagnosis by symptom. After performing necessary repairs, go to next step.
6. Rerun test situations which set DTC(s). Retrieve codes and confirm DTC P0000 (System Normal) is detected. Clear DTC(s) from PCM and TCM memory. See «CLEARING CODES»(ref-18070-S18556901412000122900000) .

DTC PRIORITY IDENTIFICATION

1. Ensure scan tool is properly connected. Select vehicle and engine selection menu (optional). Select year, engine, model and any additional information requested by scan tool.
2. Turn ignition on. Select DIAGNOSTIC TROUBLE CODES. Select ERASE. All codes should now be cleared from PCM memory. If problem has not been corrected or fault is still present, hard code will immediately be reset in PCM memory.

Enter diagnostic Mode 2 as described in RETRIEVING CODES. See WITHOUT SCAN TOOL (EXCEPT QUEST) . After retrieving codes in Mode II, turn test mode selector fully clockwise. Wait at least 2 seconds. Turn test mode selector fully counterclockwise. This will be erase DTCs from memory by switching PCM mode selector from diagnostic Mode 2, back to diagnostic Mode 1.

Enter diagnostic test Mode 2 and retrieve codes. See WITHOUT SCAN TOOL (QUEST) under RETRIEVING CODES. After codes have been retrieved, disconnect self-test harness connector (still in Mode 2) and jump terminals No. 3 and 6 together for at least 2 seconds. Disconnect jumper wire after 2 seconds. Reconnect self-test connector. This will be erase DTCs from memory.

SYSTEM READINESS TEST (SRT) CODES

Note. SRT test procedure was written specifically for use with Nissan's CONSULT diagnostic scan tool. Generic scan tools can be used but may have limited functions.

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DTC IDENTIFICATION (EXCEPT MAXIMA, PATHFINDER & QX4)

DTC IDENTIFICATION (MAXIMA)

DTC IDENTIFICATION (PATHFINDER & QX4)

Note. Time required for each diagnosis varies with road surface conditions, weather, altitude and individual driving habits.

Note. Zone "A" refers to the range where the time required, for the diagnosis under normal conditions, is the shortest. Zone "B" refers to the range where the diagnosis can still be performed if the diagnosis is not completed within Zone "A". Normal conditions consist of the following

1. Sea Level
2. Flat Road
3. Ambient Air Temperature At 68-86°F (20-30°C)
4. Diagnosis Is Performed As Quickly As Possible