Engine Controls - System & Component Testing: Other Mazda MX-5 NB

Lysholm Compressor

Remove drive belt. Rotate compressor shaft by hand. Compressor shaft should rotate smoothly. Check for cracks or damage. Replace compressor as necessary.

Charge Air Cooler (Intercooler)

Remove charge air cooler and inspect for cracks, restriction or damage. Replace as necessary.

Charge Air Cooler By-Pass (System Check)

Start engine and verify charge air cooler by-pass actuator rod is retracted. (Scheme 39) Increase engine speed to 4100 RPM. Actuator rod should extend. If actuator rod does not operate as described, check for leaking vacuum hose, faulty vacuum pump, charge air cooler, by-pass solenoid valve, faulty shutter valve or faulty actuator.

Charge Air Cooler By-Pass Actuator

Remove vacuum hose from air cooler by-pass actuator. (Scheme 39) Connect vacuum pump to actuator and apply 7.4 in. Hg of vacuum. Actuator rod should retract. If actuator does not operate, replace actuator.

Air By-Pass Valve (ABV) Actuator

Remove ABV actuator. (Scheme 39) Verify air does not flow from port "A" to port "B". (Scheme 40) Connect a vacuum pump to ABV actuator port "C" and apply 10 in. Hg of vacuum. Air should flow from port "A" to port "B". Airflow should increase as vacuum to port "C" is increased. If ABV actuator does not operate as specified, replace ABV actuator.

Charge Air Cooler By-Pass Solenoid Valve

Remove charge air cooler by-pass solenoid valve. (Scheme 39) Apply air pressure to solenoid valve port "B". (Scheme 41) Air from port "B" should flow from "C" only. Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to solenoid valve port "A". Air should flow from port "B" only. Replace solenoid valve as necessary.

Air By-Pass Valve (ABV) Vacuum Solenoid Valve

Remove ABV vacuum solenoid valve. (Scheme 39) Apply air pressure to port "A" of ABV solenoid valve. (Scheme 42) Air should not flow from port "B". Apply battery voltage to ABV vacuum solenoid valve terminals. Air should flow from port "B". Replace ABV vacuum solenoid valve as necessary.

Air By-Pass Valve (ABV) Vent Solenoid Valve

1. Remove ABV vent solenoid valve. (Scheme 39) Apply air pressure to port "A" of ABV vent solenoid valve. (Scheme 43) Air should flow from ports "B" and "C". Apply air pressure to port "B". Air should flow from port "C". Replace ABV vent solenoid valve as necessary. If ABV vent solenoid valve operates as specified, go to next step.
2. Using jumper wires, apply battery voltage to ABV vent solenoid valve terminals. Apply air pressure to port "A". Air should flow from port "B" only. Apply air pressure to port "B". Air should not flow from port "C". Replace ABV vent solenoid valve as necessary.

Scheme 39

Scheme 40

Scheme 41

Scheme 42

Scheme 43

VARIABLE INERTIA CHARGING SYSTEM (VICS) - PROTEGE 1.8L

Note. For VICS component locations, see appropriate vacuum diagram in VACUUM DIAGRAMS article.

System Check

Connect tachometer to engine. Start engine, and let idle. Shutter valve actuator rod should be extended at idle. (Scheme 44) Gradually increase engine speed to 5000 RPM and ensure actuator rod retracts. If system actuator does not operate as specified, check for vacuum leaks. If no vacuum leaks are detected, check shutter valve and shutter valve solenoid.

Scheme 44

Solenoid Valve

Remove solenoid valve. Apply air pressure to port "B". (Scheme 45) Air should flow from "C". Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to port "B". Air should flow from port "A". Replace solenoid valve as necessary.

Scheme 45

Shutter Valve Actuator

Disconnect vacuum hose from shutter valve actuator. (Scheme 44) Connect vacuum pump to actuator. If rod does not move, disconnect rod and check rod and valve for freedom of movement. Apply vacuum and verify shutter valve rod retracts. Replace as necessary. DO NOT adjust shutter valve stopper bolt.

Vacuum Chamber

Remove vacuum chamber. Visually inspect vacuum chamber for clogging, cracks and damage. Apply air pressure to port "A" and ensure air flows from port "B". (Scheme 46) Apply air pressure to port "B". Air should flow from port "A". Replace vacuum chamber as necessary.

Scheme 46

VARIABLE INERTIA CHARGING SYSTEM (VICS) - MIATA

Note. For VICS component locations, see appropriate vacuum diagram in VACUUM DIAGRAMS article.

Connect tachometer to engine. Start engine, and let idle. Shutter valve actuator rod should be extended at idle for 5 seconds. After 5 seconds, Shutter valve actuator rod should retract. Gradually increase engine speed to 5250 RPM and ensure actuator rod extends. If system actuator does not operate as specified, check for vacuum leaks. If no vacuum leaks are detected, check for DTC P1523. Diagnose and repair as necessary. If DTC P1523 is not present, use scan tool in SIMULATION TEST mode to actuate solenoid valve. Listen to solenoid while actuating with scan tool. If solenoid clicks, check vacuum actuator, vacuum chamber and vacuum lines. If solenoid does not click, check solenoid. Repair or replace as necessary.

Actuator Check

Disconnect vacuum hose. Using vacuum pump, apply vacuum to actuator. See VICS OPERATION table. If actuator does not operate properly, replace actuator and recheck.

VICS OPERATION

Solenoid Check

Remove solenoid. Check flow between solenoid valve port "B" and "C". (Scheme 41) Flow should exist. Using jumper wires, connect battery voltage to solenoid terminal "A" and battery ground to terminal "B". Check flow between solenoid valve port "A" and "B". Flow should exist. If flow is not as specified, replace solenoid.

1. Start engine. Check Variable Resonance Induction System (VRIS) shutter valve actuator rod positions. For 626, see VACUUM DIAGRAMS article. For Millenia (Scheme 47) On all models, rods should not be pulled. If shutter valve actuator rods are not pulled, go to step 4. If shutter valve actuator rods are pulled, go to next step.
2. Turn ignition off. Connect New Generation Star (49 T088 0A0) scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Check for Diagnostic Trouble Codes (DTCs). See appropriate SELF-DIAGNOSTICS - INTRODUCTION article. If any DTCs are present, repair as necessary. If no DTCs are present, go to next step.
3. Start engine and run at idle. Using scan tool, select SIMULATION TEST and turn both VRIS solenoid valves on. Listen for solenoid clicking noise. If both solenoids click, check shutter valve actuators. If solenoids do not click, check solenoid valves.
4. Start engine and operate at idle. Check operation of shutter valve actuators No. 1 and 2 at specified engine speed. See «VRIS RPM SPECIFICATIONS (MILLENIA 2.5L & 626 2.5L)»(ref-91104-S21802565962001030200000) table. If actuators do not operate as specified, check for DTCs. See appropriate SELF-DIAGNOSTICS - INTRODUCTION article. Repair as necessary. If no DTCs are present, check VRIS components and Throttle Position (TP) sensor.

VRIS RPM SPECIFICATIONS (MILLENIA 2.5L & 626 2.5L)

Check Valve

Remove check valve. For 626, see VACUUM DIAGRAMS article. For Millenia (Scheme 47) On all models, apply air pressure to port "A" (White port) of check valve. Air should flow from port "B". Apply air pressure to port "B" (Green port) of check valve. Air should not flow from port "A". Replace check valve as necessary.

Shutter Valve Actuators

Disconnect vacuum hose from shutter valve actuators No. 1 and 2. For 626, see VACUUM DIAGRAMS article. For Millenia (Scheme 47) On all models, connect vacuum pump to actuator. Apply vacuum to each actuator separately and verify shutter valve rod retracts. Ensure both shutter valves move freely. Replace actuator as necessary.

Remove solenoid valve. Apply air pressure to port "B". (Scheme 45) Air should flow from "C". Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to port "B". Air should flow from port "A". Replace solenoid valve as necessary.

Millenia 2.5L is equipped with one vacuum chamber. 626 2.5L is equipped with 2 vacuum chambers. Remove vacuum chamber. Visually inspect vacuum chamber for clogging, cracks and damage. Replace as necessary.

Scheme 47

For system check, see appropriate test in SELF-DIAGNOSTICS - PROTEGE 1.6L article.

One Way Check Valve Check

Remove one way check valve. Blow in valve into direction of arrow. Air should flow. Blow into valve in opposite direction. Air should not flow. If flow is not as specified, replace valve.

Shutter Valve Actuator Check

Disconnect vacuum hose from actuator. Connect a vacuum pump to actuator. Watch actuator rod and apply vacuum to actuator. See SHUTTER VALVE ACTUATOR CHECK table. If actuator does not operate as specified, replace actuator. If system is not working properly but actuator is okay, check vacuum lines.

SHUTTER VALVE ACTUATOR CHECK

Note. Perform VTCS solenoid check only when directed by SELF-DIAGNOSTICS testing.

VTCS Solenoid Check

Remove solenoid. Check solenoid airflow. (Scheme 48) Apply battery voltage to solenoid. Check airflow. (Scheme 48) If solenoid is okay, check vacuum lines. Repair as necessary. If no problem is found, Check for open or short in wiring. See WIRING DIAGRAMS article. Repair as necessary.

Scheme 48

Ground Circuit Checks

1. Using an ohmmeter, check ground circuits to PCM for continuity to ground. See appropriate wiring diagram in WIRING DIAGRAMS article to determine PCM ground terminals. See «PCM LOCATIONS»(ref-91104-S26093420262001030200000) table. If continuity does not exist, repair open circuit to ground.
2. Using a voltmeter, touch negative lead to a good ground. Touch positive lead to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltage reading is more than one volt, check for open circuit, corrosion, or loose connection on ground lead.

Power Circuit Checks

1. Using a voltmeter, check for battery voltage between PCM constant battery power terminals and ground. See appropriate wiring diagram in WIRING DIAGRAMS article to determine PCM power terminals. See «PCM LOCATIONS»(ref-91104-S26093420262001030200000) table. If battery voltage is not present, check PCM power supply fuse. If fuse is okay, check for open in power supply or PCM wiring.
2. Turn ignition on. Using a voltmeter, check for battery voltage between PCM ignition power terminals and ground. If battery voltage is not present, check power supply fuse(s). If fuse is okay, check for an open in wiring between fuse and PCM, or check for a defective ignition switch.
3. Connect voltmeter between ground and PCM start (crank) signal terminal. Turn ignition switch to START position. Battery voltage should be present between PCM start terminal and ground only when ignition switch is in START position. If voltage is not present, check fuse(s). If fuse is okay, check for open circuit in wiring harness between fuse and PCM. If wiring harness is okay, check for a defective ignition switch.

PCM LOCATIONS

BRAKELIGHT SWITCH

Disconnect brakelight switch connector. Using ohmmeter, check continuity between brakelight switch terminals. With brake pedal released, continuity should not exist. With brake pedal depressed, continuity should exist. If continuity is not as specified, replace brakelight switch.

Miata & Protege 1.6L

1. Remove and inspect camshaft position sensor. Clean off any metal particles or shavings. Reinstall sensor.
2. Connect scan tool. Start engine. Using scan tool, enter vehicle info and connect scan tool leads to PCM. See «CMP/PCM TERMINAL IDENTIFICATION»(ref-91104-S14916027552001030200000) table. Select DIGITAL MEASUREMENT SYSTEM, then FREQUENCY METER. Press link key to select RPM PID. Select PID/DATA MONITOR, then PCM. Press START.
3. Frequency meter should be displayed. Ensure threshold voltage is 2 volts and DC voltage is selected. Frequency should match specifications. See «CMP FREQUENCY SPECIFICATIONS»(ref-91104-S07442298102001030200000) table.
4. Change scan tool threshold voltage to 6 volts. Ensure frequency is 0 Hz. If frequency is out of specifications, check wiring for open or short circuit. Check camshaft pulley for damage. Repair as necessary.

CMP/PCM TERMINAL IDENTIFICATION

CMP FREQUENCY SPECIFICATIONS

Millenia 2.3L

1. CMP sensor is located on right front of engine. Remove CMP sensor, leaving electrical connector connected. Using analog voltmeter (or oscilloscope), connect negative lead to CMP sensor ground (CMP body or Black/Blue wire).
2. With positive voltmeter lead, backprobe Blue/Red wire at CMP connector. Turn ignition on. Rotate CMP shaft and observe voltage reading. Voltmeter should indicate a voltage pulse (5 volts) per revolution. Replace CMP sensor as necessary.

Millenia 2.5L

1. CMP sensor is located inside of distributor. Remove distributor, leaving electrical connector connected. Using analog voltmeter (or oscilloscope), connect negative lead to CMP sensor ground (CMP body or Black/Blue wire).
2. With positive voltmeter lead, backprobe Yellow/Blue wire at CMP connector. Turn ignition on. Rotate CMP shaft and observe voltage reading. Voltmeter should indicate one voltage pulse (5 volts) per revolution. Replace distributor as necessary.

Protege 1.8L

Disconnect CMP sensor harness connector. CMP sensor is located in timing belt cover, in upper front of engine. Using ohmmeter, measure resistance between component terminals. Resistance should be 950-1250 ohms. Replace as needed. If sensor is okay, check for open or short circuit in wiring between sensor and PCM. Repair as necessary.

626 2.0L

Disconnect CMP sensor harness connector. CMP sensor is located in timing belt cover, in upper front of engine. Using ohmmeter, measure resistance between component terminals. Resistance should be 950-1250 ohms. Replace as needed.

626 2.5L

Disconnect CMP sensor harness connector. CMP sensor is located next to right timing pulley. Using ohmmeter, measure resistance between component terminals. Resistance should be approximately 550 ohms. Replace as needed.

Millenia

Closed throttle position switch is part of Throttle Position (TP) sensor. To test closed throttle position switch, check TP sensor continuity. See THROTTLE POSITION SENSOR (TP) in ON-VEHICLE ADJUSTMENTS article. Check TP sensor adjustment before replacing TP sensor.

Miata, Protege & 626

Disconnect clutch switch connector. Using ohmmeter, check continuity between switch terminals. With clutch pedal depressed, continuity should exist. With clutch pedal released, continuity should not exist. If continuity is not as specified, replace clutch switch.

CRANKSHAFT POSITION (CKP) SENSOR

1. CKP sensor is located on front of engine, near crankshaft pulley. Disconnect CKP sensor connector. Using ohmmeter, measure resistance between terminals "A" and "B" at CKP sensor. (Scheme 49) Resistance should be as specified. See «CRANKSHAFT POSITION SENSOR RESISTANCE»(ref-91104-S21410012792001030200000) table.
2. If resistance is not as specified, replace CKP sensor. On Millenia 2.3L, when installing CKP sensor, adjust air gap to.040-.080" (1.0-2.0 mm). On all models except Millenia 2.3L, when installing CKP sensor, adjust air gap to.020-.060" (.5-1.5 mm).

CRANKSHAFT POSITION SENSOR RESISTANCE

Scheme 49

EGR BOOST SENSOR

See EXHAUST GAS RECIRCULATION (EGR) SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS

Except Miata & Protege

Remove ECT sensor. Place ECT sensor and thermometer in a container of water. Connect ohmmeter between ECT sensor terminals. Slowly heat water. Observe resistance reading at specified temperatures. See ENGINE COOLANT TEMPERATURE (ECT) SENSOR SPECIFICATIONS table. If resistance is not as specified, replace ECT sensor.

Miata & Protege

1. Coolant temperature sender is part of ECT sensor. Remove ECT sensor. ECT sensor is located on left side of engine. Place ECT sensor and thermometer in a container of water. Connect ohmmeter between ECT sensor terminals "A" and "B". (Scheme 50)
2. Slowly heat water. Observe resistance reading at specified temperatures. See «ENGINE COOLANT TEMPERATURE (ECT) SENSOR SPECIFICATIONS»(ref-91104-S18506167122001030200000) table. If resistance is not as specified, replace ECT sensor.
3. To check coolant temperature sender portion of ECT sensor, measure resistance between ground and ECT sensor terminal "C". (Scheme 50) Resistance should be 152-242 ohms with sensor temperature at 122°F (50°C). Replace ECT sensor as necessary.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR SPECIFICATIONS

Scheme 50

FUEL TANK PRESSURE SENSOR

1. Connect NGS scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Turn ignition on. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD. Select FTP V PID.
2. With 2 psi (6.7 kPa) of pressure applied to sensor, voltage should be 4-5 volts. With 0 psi (0 kPa) of pressure applied to sensor, voltage should be 2.3-2.8 volts. With 2 in. Hg of vacuum applied to sensor, voltage should be.45-.55 volt. If all voltage readings are as specified, fuel tank pressure sensor is functioning properly. If any voltage reading is not as specified, go to next step.
3. Turn ignition off. Check continuity of circuits between fuel tank pressure sensor wiring harness connector and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity exists in all circuits, go to next step. If continuity does not exist in one or more circuits, repair wiring harness as necessary.
4. Turn ignition on. Measure voltage at terminal "B" at fuel pressure sensor wiring harness connector. (Scheme 51) Voltage should be less than one volt. Measure voltage at terminal "C" at fuel tank pressure sensor wiring harness connector. Voltage should be 4.5-5.5 volts. If voltage is as specified, replace fuel tank pressure sensor. If voltage is not as specified, locate and repair short circuit in wiring harness. See appropriate wiring diagram in WIRING DIAGRAMS article.

Scheme 51

Miata

1. Warm engine to normal operating temperature. Connect NGS scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD.
2. Turn ignition on. Select FHO2S PID for front sensor or RHO2S PID for rear sensor. See «HO2S VOLTAGE (MIATA)»(ref-91104-S15473984812001030200000) table. If voltage is not as specified, check wiring harness between PCM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are found, replace HO2S.
3. To test HO2S heating element, allow sensor to cool to room temperature. Disconnect HO2S connector. Using ohmmeter, measure resistance between sensor terminals "C" and "D". (Scheme 52) Resistance should be about 16 ohms with sensor temperature at 68°F (20°C). If resistance is not as specified, replace HO2S.

HO2S VOLTAGE (MIATA)

Scheme 52

1. Warm engine to normal operating temperature. Connect scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD.
2. Turn ignition on. Select HO2S PID to be checked. See «HO2S PID IDENTIFICATION (MILLENIA)»(ref-91104-S34930923412001030200000) table. Voltage should be.5-1.0 volt under acceleration and 0-.5 volt under deceleration. If voltage is not as specified, check wiring harness and connector between PCM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are found, replace HO2S.
3. To test HO2S heating element on 2.5L, go to next step. To test HO2S heating element on 2.3L, allow sensor to cool to room temperature. Disconnect HO2S connector. Using ohmmeter, measure resistance between sensor terminals "B" and "C" for front sensor or terminals "C" and "D" for rear sensor. (Scheme 53) Resistance should be about 6 ohms with sensor temperature at 68°F (20°C). If resistance is not as specified, replace HO2S.
4. To test HO2S heating element on 2.5L, allow sensor to cool to room temperature. Disconnect HO2S connector. Using ohmmeter, measure resistance between sensor terminals "C" and "D". (Scheme 54) Resistance should be about 6 ohms with sensor temperature at 68°F (20°C). If resistance is not as specified, replace HO2S.

HO2S PID IDENTIFICATION (MILLENIA)

Scheme 53

Scheme 54

Protege

1. Warm engine to normal operating temperature. Connect NGS scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD.
2. Turn ignition on. Select FHO2S PID for front sensor or RHO2S PID for rear sensor. See «HO2S VOLTAGE (PROTEGE)»(ref-91104-S36259218292001030200000) table. If voltage is not as specified, check wiring harness between PCM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are found, replace HO2S.
3. To test HO2S heating element, allow sensor to cool to room temperature. Disconnect HO2S connector. On 1.6L, measure resistance between HO2S terminals "B" and "C" for front sensor or "C" and "D" for rear sensor. (Scheme 55) Resistance should be about 6 ohms at 68°F (20°C). If resistance is not as specified, replace HO2S.
4. On 1.8L, measure resistance between HO2S terminals "D" and "C". (Scheme 52) Resistance should be about 16 ohms. On all models, if resistance is not as specified, replace HO2S.

HO2S VOLTAGE (PROTEGE)

Scheme 55

626 2.0L (Using Breakout Box)

1. Warm engine to normal operating temperature. Turn ignition off. Connect 104-Pin Breakout Box (49 UN01 130) to PCM. Measure voltage at PCM terminal No. 60 for front sensor or No. 35 for rear sensor. See «HO2S VOLTAGE (626 2.0L)»(ref-91104-S11704172062001030200000) table.
2. If voltage is not as specified, check wiring harness and connector between PCM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are found, replace HO2S.
3. To test HO2S heating element, allow sensor to cool to room temperature. Disconnect HO2S connector. Using ohmmeter, measure resistance between terminals "C" and "D" for 4-terminal sensor or "B" and "C" for 3-terminal sensor. (Scheme 56) Resistance should be about 6 ohms at 68°F (20°C). If resistance is not as specified, replace HO2S.

HO2S VOLTAGE (626 2.0L)

Scheme 56

626 (2.5L)

1. Warm engine to normal operating temperature. Connect NGS scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD.
2. Turn ignition on. Select HO2S Parameter Identification (PID) to be checked and note voltage reading. See «HO2S PID IDENTIFICATION (626 2.5L)»(ref-91104-S41486001042001030200000) table. See PIN VOLTAGE/PID VALUE CHARTS article. If voltage is not as specified, check wiring harness and connector between PCM and HO2S. Also check intake manifold system, fuel system and self-diagnostic system. Repair as necessary. If no problems are found, replace HO2S.
3. To test HO2S heating element, allow sensor to cool to room temperature. Disconnect HO2S connector. Using ohmmeter, measure resistance between terminals "C" and "D" for rear sensor. (Scheme 57) Resistance should be about 6 ohms at 68°F (20° C). If resistance is not as specified, replace HO2S.

HO2S PID IDENTIFICATION (626 2.5L)

Scheme 57

Miata, Millenia 2.5L, Protege 1.6L & 626

Locate and remove IAT sensor from air cleaner housing. Place IAT sensor and thermometer in a container of water. Connect ohmmeter between IAT sensor terminals. Slowly heat water. Observe resistance at specified temperatures. See INTAKE AIR TEMPERATURE SENSOR SPECIFICATIONS (MIATA, MILLENIA 2.5L, PROTEGE 1.6L & 626) table. If resistance is not as specified, replace IAT sensor.

INTAKE AIR TEMPERATURE SENSOR SPECIFICATIONS (MIATA, MILLENIA 2.5L, PROTEGE 1.6L & 626)

1. Vehicle is equipped with 3 different IAT sensors. Each IAT sensor has unique resistance characteristics. One IAT sensor is located in air filter housing, another sensor is located in dynamic chamber at right rear of engine, and remaining IAT sensor is located in Lysholm compressor on top right of engine.
2. Remove IAT sensor(s) to be tested. Place IAT sensor and thermometer in a container of water. Connect ohmmeter between IAT sensor terminals. Slowly heat water. Observe resistance reading at specified temperatures. See «IAT SENSOR RESISTANCE (MILLENIA 2.3L)»(ref-91104-S27351087112001030200000) table. If resistance is not as specified, replace IAT sensor.

IAT SENSOR RESISTANCE (MILLENIA 2.3L)

IAT sensor is part of Mass Airflow (MAF) sensor. Disconnect MAF sensor connector. Using ohmmeter, measure resistance between MAF sensor terminals "C" and "D". (Scheme 58) Resistance should be 2210-2690 ohms. If resistance is not as specified, replace MAF sensor.

Scheme 58

Miata, Millenia & 626 2.5L

Disconnect knock sensor connector. Using ohmmeter, measure resistance between knock sensor terminal "A" (Red wire on Millenia 2.3L, White wire on all others) and knock sensor body. Resistance should be about 560,000 ohms at 68°F (20°C). If resistance is not as specified, replace knock sensor.

1. MAP sensor is located in right rear of engine compartment. Connect NGS scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Turn ignition on. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD. Select MAP V PID.
2. With 29.5 psi (100 kPa) of pressure applied to sensor, voltage should be 4-5 volts. With 0 psi (0 kPa) of pressure applied to sensor, voltage should be 2.3-2.8 volts. With 25.6 in. Hg of vacuum applied to sensor, voltage should be.9-1.1 volts. If all voltage readings are as specified, MAP sensor is functioning properly. If any voltage reading is not as specified, go to next step.
3. Turn ignition off. Check continuity of circuits between MAP sensor wiring harness connector and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity exists in all circuits, go to next step. If continuity does not exist in one or more circuits, repair wiring harness as necessary.
4. Turn ignition on. Measure voltage at terminal "B" at MAP sensor wiring harness connector. (Scheme 51) Voltage should be 4.5-5.5 volts. Measure voltage at terminal "C" at fuel tank pressure sensor wiring harness connector. Voltage should be less than one volt. If voltage is as specified, replace MAP sensor. If voltage is not as specified, locate and repair short circuit in wiring harness. See appropriate wiring diagram in WIRING DIAGRAMS article.

MASS AIRFLOW (MAF) SENSOR

1. Visually check MAF sensor for cracks or damage. If any damage is present, replace MAF sensor. If no damage is present, turn off all accessories. Connect New Generation Star (NGS) scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Turn ignition on.
2. Using scan tool, select PID/DATA MONITOR AND RECORD function. Select MAF V PID and record value while operating vehicle under specified conditions. See «MASS AIRFLOW (MAF) SENSOR VOLTAGE»(ref-91104-S40949555122001030200000) table. If voltage is not as specified, check continuity of each circuit between MAF sensor and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If continuity exists in all circuits, replace MAF sensor.

MASS AIRFLOW (MAF) SENSOR VOLTAGE

Protege & 626

Disconnect neutral switch. Using ohmmeter, check continuity between switch terminals. Ensure continuity exists with transmission in Neutral and does not exist in any other gear. Replace switch as necessary.

Millenia, Protege & 626

Disconnect power steering pressure switch connector. Connect ohmmeter between PSP switch and ground. Start engine and operate at idle. Turn steering wheel from side to side and observe ohmmeter. Continuity should exist when steering wheel is turned. Continuity should not exist when steering wheel is straight ahead. If continuity is not as specified, replace PSP switch.

THROTTLE POSITION SENSOR

See ON-VEHICLE ADJUSTMENTS article for TP sensor testing and adjustment procedures.

626 2.0L A/T

See appropriate article in TRANSMISSIONS for testing and adjustment procedures.

Miata, Millenia, Protege & 626 2.5L

1. Check for starter operation with ignition switch in START position and shift lever in "P" and "N" position only. Ensure back-up lights illuminate with ignition in ON position and selector lever in "R".
2. To test switch, disconnect transmission range switch connector. Check for continuity between specified terminals at transmission range switch. (Scheme 59), (Scheme 60) or (Scheme 61). If continuity is not as specified, replace switch.

Scheme 59

Scheme 60

Scheme 61

Miata, Millenia, Protege & 626

VSS is located on side of transaxle (transmission on Miata). Disconnect negative battery cable. Disconnect VSS connector. Rotate front wheels (rear wheels on Miata) and measure voltage between sensor terminals. (Scheme 62) If voltmeter needle does not fluctuate, replace sensor.

Scheme 62

Note. The fuel pump relay mounting lock is easily broken when relay is removed. Test relay in place and remove relay only for replacement.

Disconnect negative battery cable. Disconnect fuel pump relay connector, located above accelerator pedal. Check continuity between relay terminals "A" and "B". (Scheme 63) Continuity should exist. Using jumper wires, connect positive battery terminal to relay terminal "A". Connect relay terminal "B" to battery negative terminal. Continuity should exist between relay terminals "C" and "D". Replace relay if continuity is not as specified.

Scheme 63

Remove fuel pump relay. See FUEL PUMP RELAY LOCATIONS table. Using ohmmeter, check for continuity between relay terminals "C" and "D". (Scheme 64) Continuity should not exist. Apply battery voltage to terminal "A" and ground terminal "B". Again, check for continuity between relay terminals "C" and "D". Continuity should exist with battery voltage applied. If continuity is not as specified, replace fuel pump relay.

FUEL PUMP RELAY LOCATIONS

Scheme 64

1. Fuel pump resistor and relay (speed) is located in left rear corner of engine compartment. Disconnect fuel pump resistor and relay connector. To check fuel pump resistor, measure resistance between relay terminals "A" and "B". (Scheme 65) Resistance should be.38-.42 ohm. If resistance is not as specified, replace fuel pump resistor and relay.
2. To check relay, check for continuity between terminals "E" and "F". (Scheme 65) Continuity should not exist. Using jumper wires, apply battery voltage to connector terminals "C" and "D". Continuity should exist between terminals "E" and "F". If continuity is not as specified, replace fuel pump resistor and relay (speed).

Scheme 65

MAIN RELAY

1. Ensure main relay clicks when ignition is turned on and off. If no sound is heard, locate and remove main relay from main fuse block, in left side of engine compartment. Using ohmmeter, check continuity between terminals "C" and "D". (Scheme 64) Continuity should not exist.
2. Using jumper wires, apply battery voltage to relay terminal "A" and ground terminal "B". Check continuity between relay terminals "C" and "D". Continuity should exist with battery voltage applied. If continuity is not as specified, replace main relay.

Air By-Pass Valve (ABV) Vacuum Solenoid Valve (Millenia 2.3L)

See AIR CHARGING PRESSURE CONTROL (MILLENIA 2.3L) under AIR INDUCTION SYSTEMS.

Air By-Pass Valve (ABV) Vent Solenoid Valve (Millenia 2.3L)

See AIR CHARGING PRESSURE CONTROL (MILLENIA 2.3L) under AIR INDUCTION SYSTEMS.

By-Pass Air Solenoid Valve (Millenia 2.3L)

1. Solenoid valve is located in right rear of engine compartment. To identify solenoid valve, see appropriate illustration in VACUUM DIAGRAMS article. Disconnect vacuum hoses and connector from solenoid valve.
2. Apply air pressure to a solenoid valve port. Air should not flow from other port on valve. Using jumper wires, apply battery voltage to solenoid valve terminals. Air should flow through valve. Replace solenoid valve as necessary.

Charge Air Cooler By-Pass Solenoid Valve (Millenia 2.3L)

See AIR CHARGING PRESSURE CONTROL (MILLENIA 2.3L) under AIR INDUCTION SYSTEMS.

EGR Vent Solenoid Valve

See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS.

EGR Vacuum Solenoid Valve

See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS.

Manifold Absolute Pressure (MAP) Sensor Solenoid Valve (Millenia 2.3L)

Remove MAP sensor solenoid valve. Solenoid valve is mounted on top of right shock tower. Apply air pressure to port "B" of solenoid valve. (Scheme 41) Air from port "B" should flow from "C" only. Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to port "A" of solenoid valve. Air should flow from port "B" only. Replace solenoid valve as necessary.

Pressure Regulator Control (PRC) Solenoid Valve

Disconnect vacuum hose from PRC solenoid valve. See PRC SOLENOID VALVE LOCATIONS table. Apply air pressure to solenoid port "A". (Scheme 66) Air should flow from port "B". Using jumper wires, apply battery voltage to solenoid terminals. Apply air pressure to solenoid port "A". Air should flow through valve air filter. Replace solenoid valve as necessary.

PRC SOLENOID VALVE LOCATIONS

Scheme 66

Purge Control Solenoid

See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS.

VICS Solenoid

See appropriate VARIABLE INERTIA CHARGING SYSTEM (VICS) under AIR INDUCTION SYSTEMS .

VRIS Solenoid

See VARIABLE RESONANCE INDUCTION SYSTEM (VRIS) - MILLENIA 2.5L & 626 2.5L under AIR INDUCTION SYSTEMS.

FUEL PRESSURE RELEASE

On all models except Protege, disconnect fuel pump relay. See FUEL PUMP RELAY LOCATIONS table. On Protege, disconnect fuel pump connector located behind rear seat. On all models, start engine (if possible) and allow to die. Turn ignition off. Reconnect fuel pump relay or fuel pump connector (Protege).

FUEL PUMP RELAY LOCATIONS

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC DIAGNOSTIC PROCEDURES article.

Fuel Pump Circuit

See FUEL PRESSURE under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article.

Fuel Pressure Regulator

See FUEL PRESSURE under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article.

Pressure Regulator Control Solenoid

See PRESSURE REGULATOR CONTROL (PRC) SOLENOID VALVE under SOLENOIDS.

Fuel Injectors

Using stethoscope, listen for normal clicking sound at each injector during idle and acceleration. If clicking sound is not heard, check injector wiring circuit, or main relay and circuit.

Fuel Injector Leakage

1. Using mechanics wire, secure each fuel injector to fuel rail. Disconnect fuel injector connectors. Remove fuel rail assembly from intake manifold. See REMOVAL, OVERHAUL & INSTALLATION article. Reconnect fuel lines to fuel rail. Locate underhood Data Link Connector (DLC) in left side of engine compartment.
2. Connect a jumper wire between underhood DLC terminals F/P and GND. (Scheme 67) Turn ignition on. Tilt injectors about 60 degrees and check injector nozzles for fuel leaks. Fuel leakage should be less than one drop every 2 minutes. If fuel leakage exists, replace injector.

Scheme 67

Fuel Injector Resistance (Except Millenia)

Disconnect fuel injector connector. Using ohmmeter, measure resistance between injector terminals. Resistance should be about 13.8 ohms (Protege 1.6L) or 12-16 ohms (all others). Replace injector as necessary.

Fuel Injector Resistance (Millenia)

Disconnect fuel injector connectors. Using ohmmeter, measure resistance between injector terminals. See CHECKING FUEL INJECTOR RESISTANCE (MILLENIA) table. (Scheme 68) With sensor temperature at 68°F (20°C), resistance should be about 13.8 ohms. Replace injectors as necessary.

CHECKING FUEL INJECTOR RESISTANCE (MILLENIA)

Scheme 68

Fuel Injector Volume (Miata)

1. Disconnect battery. Remove fuel rail assembly and injectors from intake manifold. See REMOVAL, OVERHAUL & INSTALLATION article.
2. Using mechanics wire, secure each fuel injector to fuel rail. Disconnect fuel injector connectors. Reconnect fuel lines to fuel rail.
3. Using Service tool (49L018901), connect battery to each injector in turn. Using a jumper wire, connect data link connector terminals F/P and GND. Turn ignition on for 15 seconds. Measure fuel injector volume.
4. If injector output volume is less than 66-82 cc's, replace suspect injector, then check next injector. If injector output volume is 66-82 cc's or more, check next injector.
5. When all injectors have been checked, reinstall all components. Recheck system.

Fuel Cut Control System (Millenia)

1. To check system operation, connect New Generation Star (49 T088 0A0) scan tool to Data Link Connector (DLC) No. 2. DLC 2 is located under left side of instrument panel, right of steering column. Ensure engine is at normal operating temperature. Allow engine to idle. Turn A/C switch off.
2. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD. Select INJR and INJL. Scan tool will measure and display fuel injector pulse width. Increase engine speed to 4000 RPM, then quickly close throttle valve.
3. Fuel injection pulse width should be zero milliseconds until engine speeds drops to about 1200 RPM, then pulse width should return to specification noted prior to increasing engine speed. If pulse width is as specified, A/C cutoff system is functioning properly.
4. If pulse width is not as specified, measure voltage at PCM terminals 3Q (ECT sensor circuit), 3X (closed throttle position switch circuit), 4AH and 4AL (crankshaft position sensor circuit). See PIN VOLTAGE/PID VALUE CHARTS article. Repair as necessary.

1. On Millenia 2.3L, BAC valve is located on rear of front cylinder head. (Scheme 69) On Millenia 2.5L, BAC valve is located underneath throttle body. (Scheme 70)
2. On all models, ensure engine is cold. Start engine and let it idle. Idle speed should gradually decrease as engine reaches normal operating temperature. If idle speed does not decrease, check coolant hose to BAC valve. Repair as necessary. If coolant hose is okay, replace BAC valve.

Scheme 69

Scheme 70

Disconnect IAC valve connector. Using an ohmmeter, measure resistance between IAC valve terminals. See IAC VALVE RESISTANCE SPECIFICATIONS table. If resistance is not within specification, replace IAC valve.

IAC valve is part of By-Pass Control (BAC) valve. Disconnect IAC valve connector. Using an ohmmeter, measure resistance between IAC valve terminals. See IAC VALVE RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace BAC valve.

IAC VALVE RESISTANCE SPECIFICATIONS

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC DIAGNOSTIC PROCEDURES article.

System Check (Except Miata & Protege)

Check all connectors and vacuum hose routing. Check for cracks, leakage and restrictions, and repair as necessary. Start engine and operate throttle. Diaphragm of EGR control valve should not move while engine is cold. Warm engine to operating temperature. Increase engine speed to about 2000 RPM, EGR control valve diaphragm should move. If no movement is detected, check EGR system components.

System Check (Miata)

1. While listening to EGR valve, turn ignition on. If initial operation of EGR valve is present, go to next step. If initial operation of EGR valve is not present, check for DTCs. See appropriate SELF-DIAGNOSTICS article. Check EGR valve. See «EGR Valve (Miata, Protege & 626)»(ref-91104-S15054793592001030200000) .
2. Start engine. Connect scan tool and select SIMULATION TEST. Using scan tool, increase EGR step value from 0 to 40. If idle speed does not change, go to next step. If engine stumbles or stalls, go to step 4 .
3. Turn ignition off. Remove EGR valve. Reconnect EGR electrical connector. Turn ignition on. Using scan tool, increase EGR step value from 0 to 40. If EGR valve operates, clean EGR valve and passages. Install and retest. If EGR valve does not operate, replace EGR valve and retest.
4. Warm engine to operating temperature. Raise and support vehicle with drive wheels off the ground, or place vehicle on a chassis dynamometer. Using scan tool, select PID/DATA MONITOR function. Select SEGRP, RPM, VS, TP V, and ECT V PIDs. Start engine and allow vehicle to idle in gear. Ensure SEGRP PID is 0. Raise engine speed and check SEGRP. If SEGRP does not change, go to next step. If SEGRP changes, go to step 6 .
5. Check TP PID for change when throttle is depressed. Check VS PID for change when vehicle speed is increased. Check ECT PID for proper voltage when engine is at operating temperature. If any problems exist, repair component or wiring as necessary and retest.
6. Stop vehicle. Check SEGRP PID at idle. Ensure SEGRP PID is 0.

1. Connect NGS scan tool to Data Link Connector (DLC). DLC is located under left side of instrument panel, right of steering column. Turn ignition on. Using scan tool, access DIAGNOSTIC DATA LINK menu, and select PCM. Highlight and select PID/DATA MONITOR AND RECORD. Select BARO V PID.
2. Apply vacuum to sensor and monitor voltage. See «EGR BOOST SENSOR SPECIFICATIONS»(ref-91104-S14305202842001030200000) table. If all voltage readings are as specified, EGR boost sensor is functioning properly. If any voltage reading is not as specified, go to next step.
3. Turn ignition off. Check continuity of circuits between EGR boost sensor wiring harness connector and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity exists in all circuits, go to next step. If continuity does not exist in one or more circuits, repair wiring harness as necessary.
4. Turn ignition on. Measure voltage at terminal "B" at fuel pressure sensor wiring harness connector. (Scheme 71) Voltage should be less than one volt. Measure voltage at terminal "C" at fuel tank pressure sensor wiring harness connector. Voltage should be 4.5-5.5 volts. If voltage is as specified, replace fuel tank pressure sensor. If voltage is not as specified, locate and repair short circuit in wiring harness. See appropriate wiring diagram in WIRING DIAGRAMS article.

Scheme 71

EGR BOOST SENSOR SPECIFICATIONS

EGR Boost Solenoid (Millenia 2.5L, Protege & 626)

Remove EGR boost solenoid. See EGR BOOST SOLENOID LOCATIONS table. Apply air pressure to port "B" of solenoid valve. (Scheme 41) Air should flow from port "C" only. Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to port "A" of solenoid valve. Air should flow from port "B" only. Replace solenoid valve as necessary.

EGR BOOST SOLENOID LOCATIONS

EGR Position Sensor (Millenia)

EGR position sensor is part of EGR valve. Disconnect EGR position sensor connector. Disconnect vacuum hose from EGR control valve. Measure resistance between EGR position sensor terminals. See EGR POSITION SENSOR RESISTANCE table. (Scheme 72) Apply 5.9 in. Hg of vacuum to EGR position sensor and recheck resistance. If resistance is not as specified, replace EGR valve.

EGR POSITION SENSOR RESISTANCE

Scheme 72

EGR Vacuum Solenoid Valve (Millenia)

Remove EGR vacuum solenoid. See EGR VACUUM/VENT SOLENOID VALVE LOCATIONS table. Apply air pressure to a solenoid valve port. (Scheme 74) Air should not flow from other solenoid port. Using jumper wire, apply battery voltage to solenoid valve terminals. Air should flow with voltage applied. If solenoid valve does not operate as specified, replace valve.

EGR Valve (Miata, Protege & 626)

1. Using a stethoscope, listen for EGR valve initialization noise (clicks) when starting and stopping engine. If clicking noise is heard, EGR valve is functioning properly. If clicking noise is not heard, go to next step.
2. Turn ignition off. Disconnect EGR valve connector. Using an ohmmeter, measure resistance between EGR valve terminals "C" and "E", "C" and "A", "D" and "B" and between "D" and "F". (Scheme 73) Each resistance reading should be about 22 ohms.
3. If resistance is as specified, check wiring harness between EGR valve and PCM. See appropriate wiring diagram in WIRING DIAGRAMS article. If resistance is not as specified, replace EGR valve.

Scheme 73

EGR Valve (Millenia)

Warm engine to normal operating temperature and operate at idle. Disconnect and plug vacuum hose at EGR valve. Engine should run smoothly. Connect vacuum pump to EGR valve, and apply vacuum. Engine should run rough or stall. If engine does not operate as specified, replace EGR valve.

EGR Vent Solenoid Valve (Millenia & 626)

Remove EGR vent solenoid valve. See EGR VACUUM/VENT SOLENOID VALVE LOCATIONS table. Apply air pressure to port "A". (Scheme 74) Air should flow from ports "B" and "C". Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to port "A". Air should flow from port "B" only. Replace solenoid valve as necessary.

EGR VACUUM/VENT SOLENOID VALVE LOCATIONS

Scheme 74

FUEL EVAPORATION

Note. For system testing, see appropriate SELF-DIAGNOSTICS article.

Charcoal Canister (Miata)

Remove charcoal canister. Plug two smaller ports. Blow air into large port. If canister leaks, replace canister.

Charcoal Canister (Millenia & Protege)

Charcoal canister is located under rear of vehicle. Plug Canister Drain Cut Valve (CDCV) port and purge solenoid valve port. (Scheme 75)or (Scheme 76). Apply small amount of air pressure to fuel tank port on charcoal canister. If air leaks, replace charcoal canister.

Scheme 75

Scheme 76

Charcoal Canister (626)

Check for loose, missing, cracked and broken connections and parts. Repair or replace as necessary. No liquid should exist in canister.

Catch Tank (Miata)

Remove catch tank, located in right front of engine compartment. Blow air into tank and check for leaks. Replace if any leaks are present.

One-Way Check Valve (Millenia)

One-way check valve is located on top of fuel tank. Note direction of valve installation. Remove check valve. Apply air pressure to check valve port "A". (Scheme 77) Air should flow from port "B". Apply air pressure to port "B". Air should not flow from port "A". If check valve does not operate as specified, replace check valve.

Scheme 77

2-Way Check Valve (Protege)

Remove check valve, located at rear of vehicle by fuel filler. Apply air pressure to port "B". (Scheme 78) Air should flow from port "C". Apply air pressure to port "C". Air should flow from port "A". Replace 2-way check valve as necessary.

Scheme 78

Fuel Vapor Rollover Valve (Miata)

Vehicle is equipped with 1 fuel vapor valve located in top of fuel tank. Remove rear package tray trim, service cover, evap hose and valve. With valve in upright position, air should flow through valve. With valve turned upside down, air should not flow through valve. If valve does not operate as specified, replace fuel vapor rollover valve.

Fuel Vapor Rollover Valve (Millenia)

Vehicle is equipped with 2 fuel vapor valves, built into top of fuel tank. With valve in upright position, air should flow through valve. With valve turned upside down, air should not flow through valve. If fuel vapor valve does not operate as specified, replace fuel tank.

Fuel Vapor Rollover Valve (Protege & 626)

Two fuel vapor rollover valves are located in top of fuel tank. Remove fuel vapor valve. It may be necessary to remove fuel tank to access valve. Hold valve in level upright position. Blow air into port (hose barb). Air should flow through valve to lower port. Turn valve upside down. Air should not flow through valve. Replace valve as necessary.

Purge Control Solenoid Valve

Disconnect purge control solenoid valve connector. See PURGE CONTROL SOLENOID VALVE LOCATIONS table. Ensure air does not flow through solenoid valve vacuum ports. Using jumper wires, apply battery voltage to solenoid valve terminals. Apply air pressure to a solenoid valve port. Air should flow from other port. If valve does not operate as specified, replace solenoid valve.

PURGE CONTROL SOLENOID VALVE LOCATIONS

Tank Pressure Control Valve (Miata)

1. Remove Tank Pressure Control Valve (TPCV), located above fuel tank.
2. Apply air pressure to inlet port (on same side as electrical connector). At pressures less than .03 psi (.20 kPa), air should not flow. At pressures more than .14 psi (.98 kPa), air should flow through valve.
3. Using a vacuum pump, apply vacuum to inlet port. With vacuum at more than .3 in. Hg (-.98 kPa), air should flow through valve. Replace TPCV as necessary.

Tank Pressure Control Valve (Protege)

1. Remove Tank Pressure Control Valve (TPCV), located on top of fuel tank.
2. Apply air pressure to inlet port (on same side as electrical connector). At pressures less than .03 psi (.20 kPa), air should not flow. At pressures more than .14 psi (.98 kPa), air should flow through valve.
3. Using a vacuum pump, apply vacuum to inlet port. With vacuum at more than .3 in. Hg, air should flow through valve. Replace TPCV as necessary.