Electronic Control System Honda Civic III

DESCRIPTION & OPERATION

The Electronic Control Unit (ECU) receives signals from various sensors, consults appropriate memory and sends output signals to various control devices. This provides an extremely accurate control of air/fuel mixture and idle speed under all operating conditions.

The ECU is the main controlling device of electronic control system. The ECU contains memories for the basic injector durations at various engine speeds (RPM) and manifold absolute pressures (air volume). The basic injector duration is read out of the memory of the ECU. The ECU modifies the basic injector duration according to input signals from various sensors to obtain the final injector duration.

The ECU also controls cold start system, electric fuel pump and fuel cut-off systems. The ECU also contains a fail-safe system to monitor sensors and detect any abnormality in ECU. This provides safe driving even if 1 or more of the sensors are faulty or the ECU malfunctions.

There are 10 sensors used to provide operating information to the ECU in this system. These are: Crank angle sensors (TDC and CYL), manifold absolute pressure sensor (MAP), atmospheric pressure sensor, coolant temperature sensor, intake air temperature sensor, throttle angle sensor, oxygen sensor (O2), idle mixture adjuster sensor and starter switch.

The electronic control system has a self-diagnostic function to help find and fix any problems. This system uses a dash mounted PGM-FI warning light and 4 ECM mounted self-diagnostic lights. The PGM-FI warning light will glow for 2 seconds when ignition switch is turned on. The ECU is mounted below passenger seat (Civic CRX Si) or below driver's seat.

CRANK ANGLE SENSORS

Sensors and distributor are designed as an assembly to save space and weight. The unit consists of a pair of rotors (TDC and CYL), and a pick-up for each rotor. Since the rotors are coupled to the camshaft, they turn together as a unit as camshaft rotates.

The CYL sensor detects position of cylinder No. 1 as starting point for sequential injection. The TDC sensor serves to determine injection timing for each cylinder. The TDC sensor is also used to detect engine speed to read out basic discharge duration for different operating conditions.

MANIFOLD AIR PRESSURE SENSOR (MAP SENSOR)

The MAP sensor converts air pressure readings into electrical voltage signals and sends them to ECU. This information combined with signals from crank angle sensor is used to read out basic discharge duration from memory.

ATMOSPHERIC PRESSURE SENSOR (PA SENSOR)

The PA sensor converts atmospheric pressure into voltage signals and sends them to ECU. The signals then modify basic discharge duration to compensate for changes in atmospheric pressure.

COOLANT TEMPERATURE SENSOR (TW SENSOR)

The TW sensor uses a temperature dependent diode (thermistor) to measure differences in coolant temperature. Basic discharge read out is by signals sent from this sensor through ECU. Resistance of thermistor decreases with a rise in coolant temperature.

INTAKE AIR TEMPERATURE SENSOR (TA SENSOR)

The TA sensor is a thermistor and is placed in intake manifold. It acts much like coolant temperature sensor but with a reduced thermal capacity for quicker responses. Basic discharge duration read out from ECU memory is again compensated for different operating conditions by signal sent from TA sensor to ECU.

THROTTLE ANGLE SENSOR

This sensor is essentially a variable resistor. Rotor shaft is connected to throttle valve shaft and as throttle valve is moved, resistance varies, altering output voltage to control unit.

OXYGEN SENSOR

The O2 sensor, by detecting oxygen content of exhaust gas, maintains a stoichiometric air/fuel ratio. In operation, ECU receives signals and changes duration during which fuel is injected. It is mounted in exhaust manifold.

IDLE MIXTURE ADJUSTER SENSOR (IMA SENSOR)

The IMA sensor is placed in control box. Primary objective of this sensor is to maintain correct air/fuel ratio at idling when an injector is replaced. Turning adjuster changes voltage sent to ECU which in turn alters fuel discharge duration.

THROTTLE BODY

Throttle body is a 2-venturi side-draft type with primary air horn at top. Lower portion of throttle body is heated by engine coolant to prevent icing in winter. Primary throttle valve has a throttle opening sensor located on its shaft. This sensor senses changes in throttle position and signals ECU where programmed adjustments can be made to fuel injection system.

On vehicles equipped with manual transmission, a dashpot is used to prevent sudden closing of throttle during gear shifting.

IDLE CONTROL SOLENOID VALVE

When idle speed is reduced due to electrical or other loads on engine, this valve opens to by-pass additional air into intake manifold. This additional air will allow idle speed to increase to normal speed (700-800 RPM).

Operation depends upon changes in voltage at FR terminal of alternator for quicker response. After coolant temperature has reached 104°F (40°C), this valve lowers fast idle speed in steps during engine warm-up.

To prevent erratic running after engine first starts, valve is opened during cranking and immediately after starting to provide additional air into intake manifold.

FAST IDLE CONTROL SOLENOID VALVE

To prevent erratic running during engine warm-up, a higher idle speed is needed. When engine temperature is cold, this valve opens to by-pass additional air into intake manifold. This operation is dependent upon coolant temperature and atmospheric pressure.

A/T IDLE CONTROL SOLENOID VALVE

With transmission selector in any position other than "P" or "N", idle speed will tend to be lower. To compensate for this, valve opens to maintain specified idle speed (700-800 RPM) by allowing additional air to by-pass throttle valve into intake manifold.

A/C IDLE CONTROL SOLENOID VALVE

During A/C operation, this valve is turned on. It applies engine vacuum to A/C idle control diaphragm to open throttle valve, which raises idle speed to 750-850 RPM. The valve is also on when coolant temperature is low (immediately after starting), thereby ensuring stable idling regardless of position of A/C switch.

TESTING

Note. Before starting testing or trouble shooting, ensure other items that affect engine performance are within specifications. Check valve clearance, air cleaner and PCV valve. In addition, check ignition timing, function of vacuum and centrifugal advance, and condition of spark plugs. It is also necessary to obtain System Checker Harness (07999-PD60000 ) to test components.

1. Disconnect oxygen sensor connector. Start engine and warm-up for 2 minutes at 3000 RPM under no load. Raise engine speed to 4000 RPM and release throttle suddenly at least 5 times.
2. Within 1 minute after engine has been warmed up, measure voltage between connector terminal and body ground as outlined in steps 3) and 4). NOTE: If it takes more than 1 minute to complete checks, warm-up engine as outlined in step 1.
3. Raise engine speed to 5000 RPM, then lower to 2000 RPM. Immediately turn ignition off. Voltage at terminal should be less than 0.4 volts. Disconnect vacuum hose No. 21 (hose between throttle body and MAP sensor on Civic CRX Si), at throttle body. Plug throttle body fitting.
4. Connect vacuum pump to open end of vacuum hose. Apply 12 in. Hg vacuum and raise engine speed to 4000 RPM. Voltage reading should be more than 0.6 volts. Replace O2 sensor if voltages are not within specifications.

1. Disconnect vacuum hose No. 21 (hose between throttle body and MAP sensor on CRX Si), at throttle body. Plug fitting in throttle body. Connect vacuum pump to open end of vacuum hose. Disconnect wiring harness connector from control unit. Connect System Checker Harness (07999-PD60000 ).
2. Apply vacuum to MAP sensor and turn ignition on. Connect digital voltmeter positive probe to C11 terminal of system checker harness and negative probe to C14 terminal. Measure voltage between terminals. Voltage should be as shown in «MAP SENSOR VOLTAGE»(/honda/civic/iii-1983-1987/remont/testing-diagnostics/#electronic-control-system) table.

MAP SENSOR VOLTAGE

Testing Manifold Air Pressure Sens Cvic CRX Si models shown. Scheme 22

Scheme 23

1. Disconnect control unit wiring harness connector and install system checker harness. Turn ignition on. Connect digital voltmeter positive probe to C9 terminal of system checker harness and negative probe to C12 terminal. There should be 2.76-2.96 volts. (Scheme 23) (Scheme 23): Testing Atmospheric Pressure Sensor
2. If voltages are out of specifications, check for open or short circuit between ECU and atmospheric pressure sensor. Replace sensor if necessary.

IDLE MIXTURE ADJUSTER SENSOR (IMA)

Open No. 1 control box. Remove rivets holding IMA sensor. Disconnect IMA sensor 3P connector. Measure resistance between Brown and Green terminals (Green and Yellow terminals on CRX Si) of IMA sensor while turning adjusting screw. Resistance should be 250-6200 ohms. Replace sensor if resistance is not within specifications. (Scheme 24)

Testing Idle Mixture Adjuster Sens Civic CRX Si models shown. Scheme 24

INTAKE AIR TEMPERATURE/COOLANT TEMPERATURE SENS (TA/TW SENS)

1. Disconnect connector and remove TA/TW sensor from intake manifold/thermostat housing. To test sensor, suspend it in cold water and heat water slowly. Measure resistance between terminals.
2. Resistance should be 980-1340 ohms at 95°F (40°C) and 220-350 ohms at 176°F (80°C). Replace sensor if not within specifications.

Note. If either CYL or TDC sensor is faulty, they should be replaced as a set.

CYL Sensor

Disconnect CYL sensor connector. Measure resistance between White and Red terminals at sensor. Resistance should be 650-850 ohms. Measure insulation resistance between White/Red terminal of sensor and crank angle sensor housing. Resistance should be 100,000 ohms or more.

Testing CYL & TDC Sensors. Scheme 25

TDC Sensor

Disconnect crank angle sensor connector. Measure resistance between Brown and Blue terminals at sensor. Resistance should be 650-850 ohms. Measure insulation resistance between Brown/Blue terminal and crank angle sensor housing. Resistance should be 100,000 ohms or more.

Disconnect throttle angle sensor connector. Measure resistance between Yellow and Green terminals (Yellow/Red and Brown/Black terminals on CRX Si) at sensor. Resistance should be 3200-7200 ohms. If resistance is outside specified range, adjust installation position of sensor and retest. Replace sensor if necessary.

Testing Throttle Angle Sensor Civic CRX Si models shown. Scheme 26

1. Idle control solenoid valve is activated by commands from ECU. When solenoid valve opens, vacuum enters hose between air flow tube and solenoid valve. Idle speed increases for a short period after starting engine and whenever electrical loads are turned on. NOTE: Vacuum will disappear when engine RPM is raised over 1700 RPM.
2. While solenoid valve is being activated, 9 volts or more should be available between Black terminal (A) and Light Green (B) of valve leads.
3. Connect the positive battery terminal to the Black/Yellow terminal of control box and negative battery terminal to Green/Black terminal. Disconnect vacuum hose No. 28 from intake manifold. Apply vacuum to vacuum hose No. 26. It SHOULD NOT hold vacuum.
4. On Civic CRX Si models, open control box lid and disconnect wiring harness from control box. Disconnect vacuum hose form between idle control solenoid valve and No. 10 vacuum hose. Connect vacuum gauge to hose and apply vacuum. It should hold vacuum.
5. Connect battery positive terminal to control box connector Black terminal and negative terminal to Light Green terminal. Apply vacuum to hose. It SHOULD NOT hold vacuum.

Note. The fast idle control solenoid valve is open when coolant temperature is less than 5°F (-15°C). If coolant temperature is less than 104°F (40°C), solenoid is open only when atmospheric pressure is less than 26 in. Hg. Vacuum is supplied to vacuum hose between solenoid valve and air flow tube.

Scheme 27

1. When the valve is open, 9 volts or more should be available between Black/Yellow (A) and Blue/Black (B) terminals (Black (A) and Yellow (B) terminals on CRX Si) of control box No.1 wiring harness.
2. Disconnect wiring harness from No. 1 control box. Disconnect vacuum hose No. 18 from air flow tube (vacuum hose between fast idle control solenoid valve and No. 10 hose on CRX Si). Apply vacuum to the hose. It should hold vacuum. (Scheme 27) (Scheme 27): Fast Idle Ctrl Solenoid Valve Test Civic CRX Si models shown
3. Connect battery positive terminal to Black terminal of No. 1 control box coupler, and battery negative terminal to Orange terminal (Yellow terminal on CRX Si). Disconnect vacuum hose No. 23 from intake manifold. Apply vacuum. It SHOULD NOT hold vacuum.

Accord SEi Only

1. The A/T idle control solenoid valve is activated when shift lever is in any position EXCEPT "P" or "N". When solenoid valve is activated, it opens to allow vacuum into vacuum hose No. 18 between solenoid valve and air flow tube.
2. When solenoid valve is activated, 9 volts or more should be available between Black/Yellow terminal (A) and Green terminal (B) of No. 1 control box.
3. Disconnect control box No. 1 wiring harness. Disconnect vacuum hose No. 18 from air flow tube. Apply vacuum to vacuum hose No. 18. It should hold vacuum.
4. Connect battery positive terminal to Black terminal of Control Box No. 1 connector and battery negative terminal to Yellow/Black terminal. Disconnect vacuum hose No. 23. Apply vacuum to vacuum hose No. 18. It SHOULD NOT hold vacuum.

Note. Perform inspection only after engine has been warmed up to normal operating temperature (radiator fan comes on twice).

1. Disconnect vacuum hose to purge canister at the top of throttle body and connect a vacuum gauge to throttle body. Start engine and warm-up to normal operating temperature. Ensure there is NO VACUUM.
2. Check vacuum reading when throttle is opened slightly from idle. Stop engine and ensure throttle cable operates smoothly with binding or sticking. If there are any abnormalities in steps 1) and 2), check for: Excessive wear or play in throttle valve shaft. Sticky or binding throttle valve lever at full close position. Clearance between throttle stop screw and throttle lever at full close position. There should be no clearance. Purge canister port should be located upstream of primary throttle valve in full closed position.

Testing Throttle Body Assembly. Scheme 28

FUEL CUT-OFF SYSTEM

1. Start engine and warm-up to normal operating temperature. Ensure that engine idles smoothly. On vehicles equipped with manual transmission, disconnect vacuum hose from dashpot. Use a stethoscope to confirm injector operation.
2. While listening to an injector, increase engine to 3000 RPM then release throttle. Clicking of injectors should cease momentarily when throttle is released. If clicking does not cease, check ECU, throttle angle sensor, and wiring between injector and ECU.

Honda EFI Trouble Shooting Chart. Scheme 29

System Checker Harness (07999-PD60000). Scheme 30

SELF-DIAGNOSIS LIGHTS OFF PGM-FI LIGHT ON

1. Connect system checker harness between ECU and connector. Check for continuity between terminal A18 (Black/Red wire) and ground. If no continuity, repair ground circuit 2. If there is continuity, for continuity between terminal A16 (Brown/Black wire) and ground.
2. If no continuity, repair ground circuit 2. If there is continuity, check for continuity between terminal A4 (Black wire) and ground. If no continuity, repair ground circuit 3. If there is continuity, check for continuity between terminal A2 (Black wire) and ground. If there is no continuity, repair ground circuit 3.
3. If there is continuity, remove ohmmeter. Turn ignition on. Connect voltmeter positive probe to terminal B6 and negative probe to terminal A4. Measure voltage between terminal B6 (Green/Red wire) and terminal A4 (Black wire). If there is not 12 volts, repair short circuit in Green/Red wire (Green/Orange wire on CRX Si) between voltmeter and control unit.
4. If there is 12 volts, connect positive probe to terminal A15 (Yellow/Black wire) and negative probe to terminal A4 (Black wire). Measure voltage between terminals. If there is 12 volts, replace ECU and retest.
5. If there is not 12 volts, check for blown fuse to ECU, open circuit in Yellow/Black wire (Yellow/White wire CRX Si) between ECU fuse and ECU, faulty main relay, blown No. 11 fuse (No. 4 fuse on CRX Si), open circuit in Black/Yellow wire between No. 11 fuse (No. 4 fuse on CRX Si) and main relay or open circuit in main relay ground (Black wire).

SELF-DIAGNOSTIC LIGHT NO. 1 ON

Note. Before proceeding with trouble shooting, check spark plugs for mis-firing. Spark plug mis-fire can set self-diagnostic light No. 1.

1. Start engine and warm-up to normal operating temperature. Raise engine speed to 4000 RPM and quickly release throttle. Stop engine. Connect system checker harness between ECU and connector.
2. Connect positive voltmeter probe to terminal C16 (White wire) and negative probe to terminal A18 (Black/Red wire). Turn ignition on. Move throttle to wide open position and then close throttle while watching voltmeter. Voltage should raise to over .6 volt at wide open throttle (WOT) and then fall below .4 volt when throttle is closed.
3. If voltage is within specifications, replace ECU and retest. If voltage is not within specifications, test O2 sensor. Replace O2 sensor if defective. If O2 sensor tests okay, repair open circuit in White wire between O2 sensor and ECU.

SELF-DIAGNOSTIC LIGHT NO. 2 ON

Substitute a known-good ECU and test drive vehicle. If symptom/indication goes away, replace ECU.

SELF-DIAGNOSTIC LIGHTS NO. 1 & NO. 2 ON

1. Install system checker harness between ECU and connector. Turn ignition on. Connect voltmeter positive probe to terminal C15 (Red/White wire) and negative probe to terminal C14 (Blue/White wire). Measure voltage between terminals. Voltage should be 4.75-5.25 volts.
2. If voltage is not within specification, replace ECU and retest. If voltage is within specification, connect voltmeter positive probe to terminal C11 (White/Blue wire) and negative probe to terminal C14 (Blue/White wire). Measure voltage between terminals. Voltage should be 2.76-2.96 volts. If voltage is within specification, replace ECU and retest.
3. If voltage is not within specification, check for open/short circuit in White/Blue or Blue/White wires (White/Red or Brown/White wires on CRX Si) between ECU and MAP sensor. If wiring is okay, replace MAP sensor.

Note. If voltage is less than specified, check for open or poorly connected wires. If wires are okay, MAP sensor is defective.

SELF-DIAGNOSTIC LIGHT NO. 4 ON

Substitute a known-good ECU and test drive vehicle. If symptom/indication goes away, replace ECU.

SELF-DIAGNOSTIC LIGHTS NO. 1 & NO. 4 ON

Note. Check control box vacuum hose routing before proceeding with trouble shooting.

1. Ensure MAP sensor vacuum hoses are properly connected. Disconnect vacuum hose from MAP sensor and plug open end of hose. Disconnect vacuum hose No. 21 from throttle body (vacuum hose between MAP sensor and throttle body on CRX Si). Connect vacuum pump to hose and apply vacuum.
2. If hose does not hold vacuum, replace hose. If vacuum is maintained, connect system checker harness between control unit and connector. Connect positive voltmeter probe to terminal C15 (Red/White wire) and negative probe to terminal C14 (Blue/White wire). Turn ignition on and check voltage.
3. Voltage should be 4.75-5.25 volts. If voltage is not within specification, replace ECU and retest. If voltage is within specification, connect voltmeter positive probe to terminal C11 (White/Blue wire) and negative probe to terminal C14 (Blue/White wire).
4. Voltage should be 2.76-2.96 volts. If voltage is not within specification, check and repair open/short circuit in Blue/White or White/Blue wires (White/Red or Brown/White wires on CRX Si) between MAP sensor and ECU. Check for faulty MAP sensor.
5. If voltage is within specification, connect vacuum pump to MAP sensor. Ensure voltage varies as vacuum is applied. If voltage does not vary, replace MAP sensor. If voltage varies, replace ECU and retest.

SELF-DIAGNOSTIC LIGHTS NO. 2 & NO. 4 ON

1. Connect system checker harness between ECU and connector. Warm-up engine until cooling fan comes on twice. Connect voltmeter positive probe to terminal C6 (Yellow/Green wire) and negative probe to terminal C12 (Green/White wire). Voltage should be .5-.9 volt.
2. If voltage is within specification, replace ECU and retest. If voltage is not within specification, stop engine. Check for open/short circuit in Yellow/Green and Green/White wires (Red/White and Brown/Black wires on CRX Si) between coolant temperature sensor and ECU. Repair wiring as needed. Check coolant temperature sensor. Replace sensor if defective. If sensor tests okay, replace ECU and retest.

SELF-DIAGNOSTIC LIGHTS NO. 1, NO. 2 & NO. 4 ON

1. Connect system checker harness between ECU and connector. Turn ignition on. Connect voltmeter positive probe to terminal C13 (Yellow/White wire) and negative probe to terminal C12 (Green/White wire). Voltage should be 4.75-5.25 volts between terminals.
2. If voltage is not within specification, replace ECU and retest. If voltage is within specification, connect voltmeter positive probe to terminal C7 (Red/Yellow wire) and negative wire to terminal C12 (Green/White wire). Operate throttle from fully closed to fully open position while watching voltmeter.
3. Voltage should be .4-.6 volts when throttle is closed and 3.6-4.4 volts when throttle is open. If voltages are within specifications, replace ECU and retest.
4. If voltages are not within specifications, check for short/open circuit in Red/Yellow and Green/White wires (Red/Blue and Brown/Black wires on CRX Si) between ECU and throttle angle sensor. Repair wiring if necessary. If wiring checks okay, adjust or replace throttle angle sensor.

SELF-DIAGNOSTIC LIGHT NO. 8 ON

Note. Ensure crank angle sensor wiring harness is routed away from spark plug wires.

Check for open/short circuit in Orange/Blue and White/Blue wires between ECU and crank angle sensor. Repair wiring if necessary. If wiring checks okay, check crank angle sensor. Replace sensor if defective. If sensor tests okay, replace ECU and retest.

SELF-DIAGNOSTIC LIGHTS NO. 1 & NO. 8 ON

Note. Ensure crank angle sensor wiring harness is routed away from spark plug wires.

Check for open/short circuit in Orange and White wires between ECU and crank angle sensor. Repair wiring if necessary. If wiring checks okay, check crank angle sensor. Replace sensor if defective. If sensor tests okay, replace ECU and retest.

SELF-DIAGNOSTIC LIGHTS NO. 2 & NO. 8 ON

1. Connect system checker harness between ECU and connector. Connect voltmeter positive probe to terminal C5 (White/Red wire) and negative probe to terminal C12 (Green/White wire). Turn ignition on. Ensure voltage reading is correct for intake air temperature.
2. If voltage is correct, replace ECU and retest. If voltage is not correct, turn ignition off. Check for open/short circuit in White/Red and Green/White wires (Red/Yellow and Brown/Black wires on CRX Si) between intake air temperature sensor and ECU. Repair wiring if necessary. If wiring checks okay, check intake air temperature sensor. Replace sensor if defective. If sensor tests okay, replace ECU and retest.

Air Temperature Chart. Scheme 31

SELF-DIAGNOSTIC LIGHTS NO. 1, NO. 2 & NO. 8 ON

1. Connect system checker harness between ECU and connector. Turn ignition on. Connect voltmeter positive probe to terminal C13 (Yellow/White wire) and negative probe to terminal C12 (Green/White wire). Voltage should be 4.75-5.25 volts. If voltage is not within specification, replace ECU.
2. If voltage is within specification, connect voltmeter positive probe to terminal B20 (Brown wire) and negative probe to terminal C12 (Green/White wire). Voltage should be .3-4.9 volts. If voltage is within specification, replace ECU and retest.
3. If voltage is not within specification, turn ignition off. Check for open/short circuit in Brown and Green/White (Brown/Black and White/Green wires on CRX Si) wires between idle mixture adjuster sensor and ECU. Repair wiring if necessary. If wiring checks okay, check idle mixture adjuster sensor. Replace sensor if defective. If sensor tests okay, replace ECU and retest.

SELF-DIAGNOSTIC LIGHTS NO. 4 & NO. 8 ON

On Accord SEi models, test EGR control system. On Civic CRX Si models, substitute a known-good ECU and test drive vehicle. If symptom/indication goes away, replace ECU.

SELF-DIAGNOSTIC LIGHTS NO. 1, NO. 4 & NO. 8 ON

1. Connect system checker harness between ECU and connector. Turn ignition on. Connect voltmeter positive probe to terminal C13 (Yellow/White wire) and negative probe to terminal C12 (Green/White wire). Voltage should be 4.75-5.25 volts. If voltage is not within specification, replace ECU and retest.
2. If voltage is within specification, connect voltmeter positive probe to terminal C9 (Red wire) and negative probe to terminal C12 (Green/White wire). Voltage should be 2.76-2.96 volts. If voltage is within specification, replace ECU and retest. If voltage is not within specification, turn ignition off.
3. Check for open/short circuit in Brown and Green/White wires (Red/White and Brown/Black wires on CRX Si) between atmospheric pressure sensor and ECU. Repair wiring if necessary. If wiring checks okay, check atmospheric pressure sensor. Replace sensor if defective. If sensor tests okay, replace ECU and retest.

SELF-DIAGNOSTIC LIGHTS NO. 2, NO. 4 & NO. 8 ON

Substitute a known-good ECU and test drive vehicle. If symptom/indication goes away, replace ECU.

SELF-DIAGNOSTIC LIGHTS NO. 1, NO. 2, NO. 4 & NO. 8 ON

Substitute a known-good ECU and test drive vehicle. If symptom/indication goes away, replace ECU.

STARTER SWITCH SIGNAL

Connect system checker harness between ECU and connector. Turn ignition switch to START position. Connect voltmeter positive probe to terminal B13 (Blue/Red wire) and negative probe to terminal A18 (Black/Red wire). There should be battery voltage at connector. If there is not battery voltage, check for blown starter fuse or an open circuit in Blue/Red wire (Blue/White wire on CRX Si) between starter signal fuse and ECU.

ALTERNATOR FR TERMINAL SIGNAL

1. Connect system checker harness between ECU and connector. Connect voltmeter positive probe to terminal B14 (White/Red wire) and negative probe to terminal A18 (Black/Red wire). Start engine. Turn headlights on and off.
2. Voltage should drop and then raise 0-5 volts as headlights are turned on and off. If voltage does not change, stop engine. Check for continuity in White/Red wire (Blue wire on CRX Si) between alternator and ECU. If there is continuity, check for faulty alternator and/or voltage regulator. If no continuity, check for open circuit in harness.
3. Test FR terminal diode. Diode is faulty if continuity or no continuity exists in both directions between F and FR terminals of voltage regulator.

A/C SWITCH SIGNAL

Connect system checker harness between ECU and connector. Start engine. Turn blower switch and A/C switches ON. Ensure compressor and condenser cooling fan are working. Connect voltmeter positive probe to terminal B8 (Blue/Red wire) and negative probe to terminal A18 (Black/Red wire). Voltage should be 0-3 volts. If not, check for open circuit in Blue/Red wire between A/C diode connector and ECU.

Note. Voltage should be more than 9 volts if compressor or condenser cooling fan stops when power is cut-off by pressure switch or thermostat.

1. Connect system checker harness between ECU and connector. Connect voltmeter positive probe to terminal A11 (Green/Black wire) and negative probe to terminal A18 (Black/Red wire).
2. Start engine. Measure voltage at connector within 10 seconds. Voltage should be .5-1.5 volts. If voltage is as specified, raise engine speed to more than 1500 RPM. If more than 9 volts is available, replace ECU.
3. If no voltage, check for open circuit in Black/Yellow wire between No. 11 fuse (No. 4 fuse on CRX Si) and idle control solenoid valve, open circuit in Green/Black wire (Green/White wire on CRX Si) between idle control solenoid valve and ECU, or an open circuit in idle control solenoid valve. If 9 volts or more, replace ECU.

1. Connect system checker harness between ECU and connector. Start engine. Turn A/C on. Ensure compressor and condenser cooling fan are working. Connect voltmeter positive probe to terminal B1 (Blue/Yellow wire) and negative probe to terminal A18 (Black/Red wire). Voltage should be .5-1.5 volts.
2. If no voltage, check for open circuit in Black/Yellow wire between No. 11 fuse and A/C idle control solenoid valve, open circuit in Blue/Yellow wire between A/C idle control solenoid valve and ECU, or an open circuit in A/C idle control solenoid valve. If 9 volts or more is available, replace ECU.

1. Connect system checker harness between ECU and connector. Start engine. Connect voltmeter positive probe to terminal B4 (Blue/Black wire) and negative probe to terminal A18 (Black/Red wire). Voltage should be .5-1.5 volts.
2. If no voltage, check for open circuit in Black/Yellow wire between No. 11 fuse (No. 4 fuse on CRX Si) and fast idle control solenoid valve, open circuit in Blue/Black wire (Green/Yellow wire on CRX Si) between fast idle control solenoid valve and ECU, or an open circuit in fast idle control solenoid valve. If 9 volts or more is available, replace ECU.

See also:
• MAP SENSOR VOLTAGE