Engine Controls - Tests W/codes 2.4L: Diagnosis

DIAGNOSTIC TROUBLE CODES (DTCs)

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

After 3 consecutive drive cycles without a malfunction, ECM will turn off MIL, however DTC will be stored in ECM memory. If ECM does not detect a that fault for 40 drive cycles, DTC will be purged from ECM memory. ECM will purge a DTC for a misfire or fuel trim malfunction when fault is not detected for 80 drive cycles of engine 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, ECM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but driveability will be affected.

VISUAL INSPECTION

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

Perform all necessary safety precautions to prevent personal injury or vehicle damage.
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.
Check condition of air cleaner and air ducting.
Check all vacuum hoses for leaks, restrictions and proper routing.
Check EEC system wiring harness connections for corrosion, damaged pins, loose wires and improper routing.
Check ECM, sensors and actuators for physical damage.
Check engine coolant and oil level.
Check battery condition. Turn off all lights and accessories. Ensure vehicle doors are closed when measuring voltage.
Check exhaust system for leaks.

Scheme 1

Scheme 1: RETRIEVING CODES USING MIL

If use of an OBD-II type scan tool is not available, DTCs can be retrieved by changing MIL output from Mode 1 to Mode 2. Mode 1 is the normal malfunction warning mode. Mode 2 displays self-diagnostic results. 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.
To switch MIL output from Mode 1 to Mode 2, locate and gain access to ECM. See ECM LOCATION 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). MIL should now be in Mode 2. When in Mode 2 with key on and engine off, MIL should begin flashing codes (Scheme 1): Turning Test Mode Selector ECM LOCATIONS Application Location 240SX At Kick Panel Under Right Side Of Dash NOTE: DTCs retrieved by MIL may also be referred to as flash codes.
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. 1 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.
Write down codes and repair in order retrieved. To determine which circuit test to use, see «DTC IDENTIFICATION»(ref-17825-S33787007522000122900000) table. After retrieving DTCs or performing a repair, clear DTCs from ECM memory.

Scheme 2

CLEARING CODES WITHOUT SCAN TOOL

Note. Clearing code procedure will clear the following: Diagnostic trouble codes. 1st trip diagnostic trouble codes. Freeze frame data. 1st trip freeze frame data. System readiness codes. Test values. Ensure necessary freeze frame data and diagnostic trouble codes are recorded prior to clearing diagnostic information. Turning ignition off when in Mode 2 will not clear codes. Clear code procedure must be used. All diagnostic information will be erased if battery is disconnected for more than 24 hours.

Enter diagnostic Mode 2 as described in RETRIEVING CODES USING MIL . 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.

SELF-DIAGNOSTICS USING SCAN TOOL

Note. Procedures given are generic and may vary depending on equipment used. See scan tool manufacturers instructions for specifics.

CLEARING CODES USING SCAN TOOL

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.
Turn ignition on. Select DIAGNOSTIC TROUBLE CODES. Select ERASE. All codes should now be cleared from ECM memory. If problem has not been corrected or fault is still present, hard code will immediately be reset in ECM memory.

RETRIEVING CODES USING SCAN TOOL

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.
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 ECM. Select DTCs. Select DIAGNOSTIC TEST MODE RESULTS.
At this point, scan tool should display all DTCs. Write down codes in order displayed. If a communication problem exists between scan tool and ECM, check for loose power and data cables to scan tool. NOTE: If a DTC is retrieved, ECM may have stored data. See «FREEZE FRAME DATA»(ref-17825-S38626472612000122900000) . If desired, check freeze frame data before clearing codes. Clearing codes will erase freeze frame data.
To determine if codes will reappear, indicating a hard (non-intermittent) fault, clear codes and recheck for codes. See CLEARING CODES. If DTC immediately returns, malfunction is considered to be a hard fault. If a DTC does not immediately return, vehicle may need to be driven in a special pattern to cause code to reset. See «DRIVE CYCLES»(ref-17825-S24588675002000122900000) .
If one or more DTCs retrieved, service DTCs in order scan tool displayed them. Go to appropriate DTC test. If no DTCs or DTC P0000 (pass code) retrieved, proceed to «TESTS W/O CODES»(ref-17901) article.

DIAGNOSTIC WORKFLOW

Verify Complaint. Get detailed information on conditions present when fault occurred.
Check and write down DTCs and freeze frame data. Erase DTCs.
Attempt to recreate conditions present when fault occurred (test drive etc.).
Recheck DTCs and data monitor information while duplication fault conditions.
If DTCs are retrieved, perform appropriate DTC testing.
If no DTCs are retrieved or only system okay DTC is retrieved, check suspect wiring for intermittents by wiggling wiring while checking data monitor.
If no response from scan tool attempted, retrieve DTCs using MIL.
Check ECM pin voltage values. See «PIN VOLTAGE CHARTS»(ref-17824) article.
Ensure fault/symptom is repaired before returning vehicle.

DTC 1900 - RADIATOR COOLING FAN CONTROL

Low Speed Operation Turn ignition off. Disconnect radiator cooling fan relay No. 1. (Scheme 3) Start engine and allow to idle. Set temperature lever to full cold position. Turn A/C and blower switch on. Allow engine to idle for several minutes. If fan does not operate at low speed, go to next step. If fan operates at low speed, go to step 6).
Turn ignition off. Disconnect radiator cooling fan relay No. 2. Turn ignition on. Measure voltage between body ground and relay No. 2 terminals No. "2" and "5". If battery voltage is present, go to step 4). If battery voltage is not present, go to next step.
Check 10-amp fuse, 30-amp fusible link and harness connectors. Ensure continuity exists between fan relay No. 2 and battery. Repair or replace harness and/or connector as necessary.
Check Ground Circuit Turn ignition off. Disconnect fan motor harness connector. (Scheme 4) Check for continuity between fan relay terminal No. "3" and motor connector terminal "a". (Scheme 5) Check for continuity between body ground and motor connector terminals "c" and "d". If continuity is not present, repair harness or connectors. If continuity is present, go to next step.
Check Output Signal Circuit Disconnect ECM harness connector. Check for continuity between fan relay No. 2 terminal No. 1, and ECM harness connector terminal No. 14. If continuity is not present, repair harness or connector. If continuity is present, replace relay using a known good unit. If low speed cooling fan still does not operate, check ECM harness connector pins for damage or corrosion. Check radiator cooling fan motor for visual damage and repair if necessary.
High Speed Operation Turn ignition off. Reconnect radiator cooling fan relay No. 1. Disconnect radiator cooling fan relay No. 2. Turn A/C switch and blower switch off. Disconnect Engine Coolant Temperature (ECT) sensor connector. Connect a 150-ohm resistor between ECT terminals. Start engine and allow to idle for several minutes. If fan does not operate at high speed, go to next step. If fan operates at high speed, testing is complete. If symptom is still present, check radiator or thermostat for fault.
Check Power Supply Turn ignition off. Disconnect cooling fan relay No. 1. (Scheme 3) Turn ignition on. Measure voltage between ground and relay No. 1 terminals No. "2" and No. "5". If battery voltage is present, go to next step. If battery voltage is not present, check 7.5-amp fuse and 30-amp fusible link. If no faults are found, repair open or short circuit in harness or connectors between cooling fan relay and battery.
Check Ground Circuit Turn ignition off. Disconnect cooling fan motor harness connector. (Scheme 4) Check for continuity between cooling fan motor connector terminal "b" (Brown/White wire) and relay No. 1 terminal No. "3" (Brown/White wire). (Scheme 6) Check for continuity between ground and cooling fan motor connector terminals "c" and "d" (Black wire) and body ground. If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.
Check Output Signal Circuit Leave ignition off, relay and cooling fan motor harness connector disconnected. Disconnect ECM harness connector. Check for continuity between relay No. 1 terminal No. "1" (Orange/Blue wire) and ECM connector terminal No. 13. If continuity is present, go to next step. If continuity is not present, repair harness or connectors as necessary.
Check Cooling Fan Relay Connect relay terminal No. "3" to ground. (Scheme 7) Using jumper wire, apply battery voltage to terminal No. "5". Check continuity as follows: Verify continuity is present between relay terminals No. "1" and "2". Remove battery voltage from relay. Check continuity as follows: Verify continuity is not present between relay terminals No. "1" and "2". If continuity is not as specified, replace cooling fan relay. If continuity is as specified, go to next step.
Check Cooling Fan Motor With cooling fan motor disconnected, apply fused battery power to terminal "a" or "b". (Scheme 8) When ground is supplied to terminal "c" or "d", cooling fan motor should operate. If motor operates, testing is complete. If cooling fan motor does not operate, go to next step.
Disconnect ECM wiring harness connector. Check connector pins for damage or corrosion. Check all circuit connectors for clean, tight fit and service if necessary. Loosen and retighten engine ground screws.