Ecc Control System - 1.8l Turbo Nissan 200SX S12

DESCRIPTION

The Electronic Concentrated Engine Control System (ECCS) is a computerized emission, ignition, and fuel control system. A single control unit monitors a variety of sensors, including the following

1. Mass Airflow Meter
2. Crankshaft Angle Sensor
3. Temperature Sensor
4. Detonation Sensor
5. Exhaust Gas Oxygen Sensor
6. Throttle Valve Switch

The computer processes information from these sensors and controls these engine functions

1. Air Injection
2. Air Regulator Control
3. EGR Operation
4. Engine Idle Speed
5. Fuel Injectors
6. Fuel Pump Operation
7. Ignition Timing
8. Mixture Ratio

200SX Turbo ECCS Component Locations. Scheme 32

ECCS CONTROL UNIT OPERATION

The control unit is located on driver's side kick panel. The unit is not serviceable and should not be opened. Monitor lamps are provided on lower side of unit so system operation can be checked. The control unit contains memory and logic circuits that enable it to interpret sensor inputs, and control different engine systems.

AIRFLOW METER

Air mass meter measures the mass flow rate of the incoming air. Measurements are made by measuring amount of heat dissipated from the hot wire placed in the stream of intake air.

CRANKSHAFT ANGLE SENSOR

The crankshaft angle sensor, which is built into the distributor, has 2 diodes and a wave-forming circuit. When a signal rotor plate passes the space between light emitting diode (LED) and photo diode, the slit to the signal rotor plate alternately cuts the light which is sent to the photo diode from the LED. This causes a pulsating voltage which is converted into an on-off pulse by the waveforming circuit and sent to the control unit.

TEMPERATURE SENSOR

The coolant temperature sensor is located in the coolant outlet. The sensor provides a varying resistance measurement as engine temperature changes.

DETONATION SENSOR

The detonation sensor is located on passenger's side of engine block. It sends a signal when "knocking" occurs. The control unit modifies ignition timing to reduce detonation.

EXHAUST GAS OXYGEN SENSOR

This component measures the amount of unburned oxygen in the exhaust. It provides a voltage signal which is used to adjust fuel mixture (amount of injection time), so that proper combustion occurs.

FUEL TEMPERATURE SENSOR

The fuel temperature sensor is built into the pressure regulator, and senses fuel temperature. When the fuel temperature is higher than the specified level, the ECCS control unit enriches the fuel mixture.

AIR INJECTION

The Air Injection Valve (AIV) sends secondary air to the exhaust manifold, utilizing a vacuum caused by exhaust pulsation in the exhaust manifold. When exhaust pressure is below atmospheric pressure (negative pressure), secondary air is sent to the exhaust manifold. When exhaust pressure is above atmospheric pressure, reed valves prevent secondary air from being sent back to the air cleaner.

EGR OPERATION

Exhaust gas recirculation is controlled by the ECCS. A signal is sent to the vacuum control modulator, providing a regulated vacuum supply to open the EGR valve. EGR operation is affected by cylinder head temperature, throttle valve position and ignition switch position. Recirculation takes place when the engine is operated above idle with cylinder head temperatures between 135-239° F (57-115° C).

ENGINE IDLE SPEED

Idle speed is controlled by the ECCS control unit, corresponding to engine operating conditions. The ECCS control unit senses engine conditions and determines the best idle speed at each cylinder head temperature and gear position. The control unit then sends an electronic signal corresponding to the difference between the best idle speed and the actual idle speed to the AAC valve.

FUEL INJECTION

The fuel injector is a small solenoid valve, to which high-pressure fuel is supplied. The ECU controls the solenoid coil within the injector. The coil, when energized, opens a ball valve which allows fuel to pass through a swirl orifice and into the manifold.

FUEL PUMP

The ECCS control unit operates the electric fuel pump. When ignition switch is turned to the "ON" or "START" position, the fuel pump operates. If ignition is on and no signal is received from crank sensor for more than one second, the fuel pump stops. It will operate for 5 seconds before engine is cranked, and will then stop if engine is not cranked over at 20 RPM or more.

IGNITION TIMING

The ECCS control unit uses sensor input to determine correct timing. It sends a signal to a power transistor located in the coil, which permits current to flow through coil. Timing is advanced and retarded by the control unit based on sensor input, built-in programming and detonation sensor signals.

DIAGNOSIS & TESTING

WATER TEMPERATURE SWITCH

1. Remove water temperature switch
2. Check water temperature switch for proper operation.

Operating Temperature

OFF-ON = 100° (212°F).

OPERATION - SELF-DIAGNOSTIC SYSTEM

The self-diagnostic system is useful to diagnose malfunctions in major sensors and actuators of the ECCS system. The ECU constantly monitors the function of these sensors and actuators, regardless of ignition key position. If a malfunction occurs, the information is stored in the ECU and can be retrieved from the memory by turning on the diagnostic mode selector, located on the side of the ECU. The selector is also an on and off switch, yet it is operated by inserting a screw driver through the appropriate hole on the side of the ECU. (Scheme 33)

A malfunction in the system is interpreted by the number of blinks of both the Red and Green light emitting diodes (LEDs) on the BECCS control unit. (Scheme 33) Red should blink first, followed by Green. Red represents the tens digit and Green represents unit digits. For example, if Red blinks 2 times followed by Green blinking 5 times, this would represent code No. 25.

ECCS Control Units. Scheme 33

SELF-DIAGNOSTIC PROCEDURES

1. Verify that diagnosis mode selector is turned fully counterclockwise. Turn ignition switch to the "ON" position. Make sure inspection lamps on control unit stay on. If okay, proceed to next step. If no good, check harness for battery source. If harness is okay, replace control unit. Turn diagnosis mode selector fully clockwise.
2. Make sure that inspection lamps on control unit are displaying codes No. 23, No. 31 and No. 32. If not, write down the malfunctioning code. If okay, depress accelerator pedal, then release.
3. Make sure that inspection lamps on control unit are displaying code No. 31 and No. 32. Write down other codes that are flashed. Start engine. Make sure inspection lamps on control unit are displaying code No. 31. Turn air conditioner switch on and off. Lamps on control unit should be displaying code No. 44. Turn diagnosis mode selector fully counterclockwise. Turn engine off.
4. Turn one of the load switches on and off. Make sure that inspection lamps on control unit are displaying code No. 44. If not, write down any alternate code being flashed. If okay, turn diagnosis mode selector fully counterclockwise. Turn engine off. Check malfunctioning area as listed in component testing. Erase memory of self-diagnosis results.
5. On manual transmission models, depress clutch pedal, and shift gear lever from Neutral to any position, and then release clutch pedal. Depress clutch pedal again, and shift gear lever back to Neutral, and then release clutch pedal. On automatic transmission models, shift gear lever from Neutral or Park to any position, and then back to Neutral or Park. Make sure that inspection lamps are displaying code No. 44. If this code is not displayed, write down the code being flashed, and consult the corresponding repair procedure.

MEMORY ERASURE

Turn ignition switch to the "ON" position. Turn diagnosis mode selector on (fully clockwise), and keep it there for more than 2 seconds. Turn diagnosis mode selector off (fully counterclockwise), and keep it there for more than 2 seconds. Turn ignition switch off.

Scheme 34

Scheme 35

1. Visually check the air cleaner, hoses and ducts, EGR valve operation, electrical connectors, gaskets and throttle valve and switch. Start engine and warm up until water temperature indicator points to the middle of the gauge.
2. Run engine at no-load at 2000 RPM for about 2 minutes. Perform ECCS self-diagnosis. Repair or replace components as necessary. If engine does not run smoothly, clean and inspect injectors and replace if necessary.
3. If engine runs smoothly, open engine hood and run engine at 2000 RPM for about 2 minutes under no-load. Race engine 2 or 3 times under no-load, then run engine at idle speed and check against table. IDLE SPEEDS (RPM) Application Sea Level High Alt. Manual Transmission 700-800 630-720
4. If idle speed is not okay, adjust and return to step 3). If okay, check ignition timing. Timing should be 13-17° BTDC. If not okay, adjust and return to step 3). If okay, run engine under no-load at about 2000 RPM for about 2 minutes. (Scheme 34): 200SX Turbo ECCS Schematic & Vacuum Diagram Note direction of flow.
5. Make sure that even if Red lamp goes on, Green lamp on control unit goes on and off more than 9 times during 10 seconds at 2000 RPM. If not, go to step 11). If okay, go to next step.
6. Race engine 2 or 3 times under no-load and then run engine at idle speed. Check inspection lamp for Red and Green blinking simultaneously. If they don't, go to step 8). If they do, again race engine 2 or 3 times under no-load and then run engine at idle speed.
7. Check idle speeds against those listed in idle speeds table. If okay, test is complete. If no good, adjust.
8. If lamps did not blink as listed in step 6), turn off engine and remove airflow meter from vehicle. Drill a hole in plug which seals variable resistor of airflow meter and remove seal plug. Install airflow meter on vehicle. Start engine and warm up until indicator is at middle of gauge.
9. Adjust idle mixture ratio by turning variable resistor of airflow meter so that inspection lamps blink simultaneously. If found to be not adjustable, replace airflow meter. If adjustable, go to next step.
10. Turn off engine and remove airflow meter. Install a new seal plug into variable resistor hole. Install airflow meter to vehicle and return to step 3).
11. If inspection lamps failed to flash as specified in step 5), check exhaust gas sensor harness. Turn off engine and disconnect battery ground cable. Disconnect 16-pin connector from control unit.
12. Disconnect exhaust gas sensor harness connector and connect terminal for exhaust gas sensor to ground with a jumper wire. Check for continuity between terminal No. 24 of 16-pin connector and ground metal of vehicle body. (Scheme 35) (Scheme 35): 16-Pin Connector Terminals
13. If continuity does not exist, repair or replace harness and return to step 3). If continuity exists, connect 16-pin connector and battery ground. Disconnect jumper wire. Disconnect engine coolant temperature sensor harness connector. Connect a 2500-ohm resistor between harness connector terminals.
14. Start engine and warm up until water temperature indicator points to the middle of the gauge. Race the engine 2 or 3 times under no-load, and run at idle speed.
15. Check idle CO%. It should be below 8%. After checking, disconnect the resistor from terminals of temperature sensor and reconnect connector to sensor. If CO was not okay, go to step 8). If okay, go to next step.
16. Replace exhaust gas sensor and make sure that even if Red lamp goes on, Green inspection lamp goes on and off more than 9 times in 10 seconds when engine is run at 2000 RPM. If no good, replace control unit.

CRANK ANGLE SWITCH TEST - CODE 11

1. Turn ignition switch to the "ON" position. Check voltage between crank angle sensor connector terminal B and ground. Battery voltage should be present. Turn ignition switch to the "OFF" position, and check resistance between terminal D and ground. Resistance should be zero ohms. If not, check harness between crank angle sensor and control unit, and harness to the battery. If okay, go to next step.
2. With ignition switch in the "OFF" position, disconnect ECU 20-pin connector and measure the resistance between terminals No. 17 and 8. Resistance should be infinite. Connect crank angle sensor harness terminals with a jumper wire, and measure the resistance between terminals No. 17 and 8. No resistance should be present. If no good, repair or replace harness. If okay, check crank angle sensor for any damage. Visually inspect the unit. If damaged, replace. Perform self-diagnosis. If code No. 11 still flashes, replace ECU.

20-Pin Connector Terminals. Scheme 36

Scheme 37

1. Disconnect 16-pin connector and connect terminal No. 26 to ground with a jumper wire. Turn ignition to the "ON" position and measure voltage between terminals No. 31 and 26. Voltage should be 0.6-1.0 volts. see scheme 6
2. If voltage is good, go to next step. If voltage is no good, check harness for continuity. If okay, go to next step. If no good, turn ignition switch to the "ON" position and measure voltage between terminals No. 26 and 27. Battery voltage should be detected. If okay, go to next step. If not, repair harness.
3. Disconnect airflow meter connector. (Scheme 37) Apply battery voltage to terminals B and C. Measure voltage between D and C. Voltage should be 0.6-1.0 volts. If no good, replace airflow meter. If okay, go to next step. (Scheme 37): Airflow Meter Connectors (200SX)
4. Remove airflow meter. Apply battery voltage to terminals B and C. Blow air through airflow meter and measure voltage between terminals D and C. Voltage should be 1.8-2.2 volts at 66 lb. (30 kg) per hour of airflow. If not correct, replace airflow meter. If voltage reading was as indicated, replace control unit.
5. Turn ignition switch to the "OFF" position. Disconnect ECU 16-pin connector and measure the resistance between the following terminals: 26-30, 26-31, 30-31, 36-26, 36-30, 36-31. Resistance should be infinite. Connect airflow meter harness connector terminals C, E and F with a lead wire and measure the resistance between terminals No. 26-30, 26-31, and 30-31. Resistance should be zero ohms. If not, repair or replace harness. If okay, go to next step.
6. Remove airflow meter. Apply battery voltage to terminals D and E. Measure voltage between terminals B and D. (Scheme 37) Voltage should be 1.1-2.1 volts. If no good, replace airflow meter.
7. If okay, blow through airflow meter and measure voltage between terminals B and D. Voltage should be 2-4 volts. If okay, replace control unit. If no good, replace airflow meter.

AIRFLOW METER RESISTANCE VALUES

COOLANT TEMPERATURE SENSOR TEST - CODE 13

1. Disconnect 16-pin connector. Measure the resistance between terminals No. 23 and 26. If resistance readings are okay, replace control unit. If not okay, check wiring harness. If harness is okay, place the sensor into water that is maintained at the specified temperature(s) in the «COOLANT SENSOR TEMPERATURE/RESISTANCE RELATIONSHIP»(/nissan/200sx/s12-1983-1989/remont/testing-diagnostics/#ecc-control-system-18l-turbo) table. COOLANT SENSOR TEMPERATURE/RESISTANCE RELATIONSHIP °F (°C) Ohms 14°F (10°C) 8500-9500 68°F (20°C) 2300-2700 122°F (50°C) 770-870 176°F (80°C) 300-330
2. If the readings of the sensor do not match the ones in the table, replace temperature sensor. If readings match the ones in the table, sensor is good, replace the control unit.

Scheme 38

1. Disconnect 20-pin connector and check for insulation between terminals No. 3, 5 and 14 and ground. (Scheme 38) If there is no continuity, repair harness.
2. If there is continuity, check power transistor. With ohmmeter positive lead on terminals No. 1, 4, 4 and 2, continuity should be found at terminals No. 5, 2, 3 and 3 respectively. (Scheme 38) If checks are okay, perform ECCS self-diagnosis procedure. If okay, end test. If not okay, replace ECCS control unit. (Scheme 38): 200SX Power Transistor Terminals
3. If voltage was present, check harness between ECU and power transistor. Disconnect ECU 20-pin connector and check for insulation between terminals No. 3, 5 and ground. No resistance should exist. Place a lead wire across terminals No. 3 and 2 of harness connector, and measure resistance between terminals No. 3 and 5 in 20-pin connector. If no resistance is found, repair or replace harness.
4. If resistance was found, check power transistor for continuity. Refer to the «POWER TRANSISTOR CONTINUITY VALUES»(/nissan/200sx/s12-1983-1989/remont/testing-diagnostics/#ecc-control-system-18l-turbo) table for Maxima readings.

POWER TRANSISTOR CONTINUITY VALUES

View of Ignition Coil Terminals. Scheme 39

FUEL PUMP TEST - CODE 22

1. Turn ignition switch to the "ON" position and listen to the fuel pump operating sound. The sound must be heard for about 5 seconds. On 200SX Turbo, if okay, perform ECCS diagnosis. If diagnosis correct, end test. If not, replace ECCS unit. If sound was not heard, go to step 2).
2. Disconnect ECCS 15-pin connector, and check voltage between terminal No. 108 and ground when ignition switch is turned to "ON". (Scheme 40) Battery voltage should be present. If not, check harness, and replace or repair as necessary.
3. Check fuel pump for continuity between leads of fuel pump connector. If not okay, replace fuel pump. If okay, replace ECCS.
4. Turn ignition switch to "ON". Check voltage between fuel pump harness connector terminal D and ground. Battery voltage should exist for 5 seconds after turning ignition switch to "ON". If okay, go to next step. If not okay, check harness continuity between fuel pump and ground, fuel pump relay, and power source to the ECU.
5. Check ground circuit. Turn ignition switch to "OFF". Disconnect fuel pump harness connector. Check resistance between terminal E and ground. No resistance should exist. Disconnect fuel pump harness connector, and check resistance between terminals D and E. No resistance should be present. If not okay, replace fuel pump. If okay, check crank angle sensor circuit, and test again if it is necessary.

ECCS 15-Pin Connector Terminal Locations. Scheme 40

Scheme 41

1. Check harness for continuity. If no good, repair. Check throttle valve switch for continuity between terminals E and F. (Scheme 41) If there is continuity, go to next step. If there is no continuity, adjust switch so that switch turns on at idle A 250 RPM. If not adjustable, replace throttle valve switch. If adjusted, go to next step. (Scheme 41): Throttle Valve Switch Connector
2. Check for insulation between terminals E, F, and ground. If no insulation, replace throttle valve switch. If there is insulation, perform ECCS self-diagnosis, and if okay, end test.
3. Check throttle valve switch. Disconnect throttle valve switch harness connector. Check the throttle valve switch for continuity between terminals No. 25 and 18. (Scheme 40) Continuity should exist with the throttle valve at idle, and should not exist when valve is slightly open. If not, replace throttle valve switch.

IDLE SPEEDS SPECIFICATIONS

AIR CONDITIONER CHECK - CODE 31

Start engine, turn air conditioner switch to "ON", and check compressor operation. If okay, stop engine and disconnect 16-pin connector. see scheme 6 Turn ignition on and measure battery voltage between terminal No. 22 and ground. If no battery voltage, repair harness. If there is battery voltage, perform ECCS self-diagnosis. If still code 31, replace ECCS control unit.

START SIGNAL CHECK - CODE 32

Check starting system. If okay, disconnect starter motor "S" terminal. Disconnect 20-pin connector and measure voltage between terminal No. 9 and ground. There should be battery voltage. If not, repair harness. If okay, replace ECCS control unit.

DETONATION SENSOR - CODE 34

Disconnect detonation sensor harness connector. Start engine and increase engine speed while checking ignition timing. Check if ignition timing retards by 5 degrees when engine speed increases more than 2000 RPM. If not, replace ECCS control unit. If okay, check harness for continuity. If okay, replace detonation sensor.

Scheme 42

1. Check air regulator operation. When engine is cold, the shutter should be open; when warm, the shutter should be closed. If okay, end test. If not, test connector for continuity.
2. Disconnect 20-pin connector. Check voltage between terminal No. 16 and ground when ignition is in the "ON" position. (Scheme 42) If there is battery voltage, replace ECCS unit. If not, check harness and repair if necessary. If harness is okay, check air regulator. (Scheme 42): ECCS 20-Pin Connector Terminal Locations
3. Check for continuity between the 2 terminals of the connector. Resistance should be 70 ohms. If not okay, replace air regulator. If okay, check EFI harness.
4. Turn ignition switch to the "ON" position, and measure voltage at the connector of EFI harness. Battery voltage should be present between connector and ground. If not okay, repair or replace harness. If okay, replace ECCS.

INJECTOR TEST

1. Disconnect 15-pin connector. Check voltage between ground and terminals No. 101, 102, 104 and 105. see scheme 13 If there is battery voltage, check injector for clogging. Clean injector as necessary and start test again. If battery voltage was not present, check each injector for continuity. see scheme 13: ECCS 15-Pin Connector Terminal Locations
2. Check for continuity between 2 terminals of injector connector. Resistance should be approximately 3 ohms. If okay, replace injector. If not, check EFI harness for continuity. Repair or replace as needed.
3. Disconnect ECU 15-pin connector. Measure voltage between injector harness terminal and ground with the ignition to the "OFF" position. Voltage should be battery voltage. If not, check harness and fusible link. If okay, check ECU harness.
4. Check harness between ECU and connectors for continuity. Connect a lead jumper wire between injector connector terminals. Check voltage between 15-pin connector terminals No. 101, 102, 103, 104, 105, 106 and 114 and ground. If battery voltage is not present, repair or replace harness. If voltage is present, replace ECU.

BATTERY SOURCE & GROUND TEST

1. Disconnect 16-pin connector. Check voltage between terminals No. 27 and 28, 27 and 36, 35 and 36, and 35 and 28 when ignition is in the "ON" position. see scheme 14 If there is battery voltage, test is complete.
2. If not, repair harness. If harness is okay, test is complete. If no good, check EFI relay. Relay should show continuity as listed in table. If not, replace relay. see scheme 14: 16-Pin Connector Terminals
3. If not, disconnect ECU 15-pin and 16-pin connectors. Check for continuity between terminals No. 28, 36, 107, 109, 112 and 113 and ground. Resistance should be zero ohms. If not, check that the ground terminal is securely mounted. If it is, replace harness. If it is not securely mounted, re-mount.
4. If resistance at ECU terminals was as specified, check battery voltage. Securely connect ECU 15-pin and 16-pin connectors. Turn ignition switch to the "ON" position and measure the voltage between terminals No. 27 and 35 and ground. Battery voltage should be read. If okay, inspection ends. If not okay, check EFI control relay.
5. Measure the voltage at terminal No. 6 of 20-pin connector for 6 seconds when ignition switch is turned to "OFF" from the "ON" position. Voltage should be 12 volts when ignition is turned to the "OFF" position, and zero volts when ignition is turned to the "ON" position. If not okay, check terminal polarity of battery, check harness between ECU No. 6 and EFI relay.
6. Check for continuity at EFI relay. Relay continuity should be as stated in the EFI RELAY CONTINUITY table. If okay, check the harness between ECU terminals No. 27 and 35 and EFI relay. see scheme 14 If not, replace EFI relay.

EFI RELAY CONTINUITY

EXHAUST GAS SENSOR TEST

1. Disconnect battery ground cable. Disconnect exhaust gas sensor harness connector and connect center terminal to ground. Disconnect 16-pin connector and check continuity between terminal No. 24 and ground. see scheme 14 Continuity should exist. If not, check ECCS harness. If harness is okay, replace exhaust gas sensor.
2. Disconnect 15-pin connector and check voltage between terminal No. 115 and ground when ignition is in the "ON" position. see scheme 13 If there is battery voltage, test is complete. If not, measure the resistance between terminals of exhaust gas sensor heater connector. Resistance should be between 2.62-3.12 ohms. If okay, check harness. If not okay, replace exhaust gas sensor.
3. If resistance across sensor was okay, turn ignition switch to the "ON" position and measure the voltage at the harness connector. Battery voltage should be present. If not, check EFI relay, harness between EFI relay and exhaust gas sensor, and harness between EFI relay and battery. If voltage was okay, check harness between ECU terminal No. 115 and exhaust gas sensor. Jump harness to ground with a lead wire, and measure resistance between ECU 15-pin connector terminal No. 115 and ground. Continuity should exist. If not, repair or replace. If resistance was not present, replace ECU.

IDLE-UP SOLENOID VALVE TEST

1. Disconnect ECCS 20-pin connector, and check voltage between terminal No. 2 and ground when ignition switch is turned to "ON". see scheme 15 If not okay, go to next step. If okay, with ignition still on, measure the voltage between terminal No. 19 and ground. With the heater fan switch on, voltage should be 12 volts, and with the fan off, voltage should be zero volts. If not okay, check diodes for open circuit. Check switches for battery source. Repair or replace as necessary. Go to next step. see scheme 15: ECCS 20-Pin Connector Terminal Locations
2. Check idle-up solenoid valve for continuity. Resistance between the terminals of the solenoid valve connector should be 30 ohms. If not, replace. If okay, check EFI harness for continuity and main harness for battery source. Check EFI relay. Repair or replace as needed.

Checking Idle-Up Solenoid Valve Continuity. Scheme 43

PRESSURE REGULATOR SOLENOID VALVE TEST

1. Disconnect cylinder head temperature sensor harness connector and connect a lead wire between the terminals of cylinder head temperature sensor harness connector.
2. Disconnect vacuum hose between pressure regulator and solenoid valve. Start engine and make sure that vacuum does not exist for 3 minutes. If okay, test is complete. If not, go to next step.
3. Confirm that ignition switch is in the "OFF" position, and check for continuity between regulator harness connector terminals No. 80, 83 and 85 and ground. Turn ignition switch to the "ON" position, and measure voltage between harness terminals No. 81 and 84 and ground. Battery voltage should be present. Disconnect starter motor "S" terminal. Turn ignition switch to "START", and measure voltage between harness terminal No. 82 and ground. Battery voltage should be present.
4. Check pressure regulator control solenoid valve for continuity. Resistance between terminals of solenoid valve connector should be zero ohms.
5. Check vacuum switch for proper operation. Resistance should be infinite when vacuum is above 3.15 in. Hg, and zero ohms when below 3.15 in. Hg. If solenoid valve, vacuum switch, circuit and hoses are okay, replace pressure regulator control modulator.
6. Check harness between solenoid valve and ECU terminal. Jump solenoid harness connector to ground with a lead wire. Measure continuity between 20-pin connector terminal No. 19 and ground. Resistance should be zero ohms. If not, repair or replace solenoid valve. If continuity exists, replace ECU.

200SX Turbo ECCS Wiring Diagram. Scheme 44

See also:
• COOLANT SENSOR TEMPERATURE/RESISTANCE RELATIONSHIP