COMPUTERIZED ENGINE CONTROLS
Note. To identify circuits referenced in the following ground and power tests, see WIRING DIAGRAMS article.
Ground Circuits
- Using DVOM, check for continuity to ground at PCM ground terminals. see scheme 1 Resistance should be zero ohms. If resistance is not zero ohms, repair open in ground circuit. If resistance is as specified, go to next step.
- Connect negative lead to a known-good ground. Backprobe positive lead to each PCM ground terminal. With vehicle running, DVOM should indicate less than one volt. If DVOM indicates more than one volt, check for open, short to voltage, corrosion or loose connection in ground circuit. If DVOM indicates less than one volt, see «POWER CIRCUITS»(ref-128963-S04636505912001110800000).
Power Circuits
- Using DVOM, check for battery voltage between PCM power terminals and ground. see scheme 1 See WIRING DIAGRAMS article. If battery voltage is not present, check for open fuse or fusible link. If fuse or fusible link is okay, go to next step.
- Turn ignition switch to ON position. Using DVOM, check for battery voltage at PCM ignition power terminals. If battery voltage is not present, check IGN fuse. If fuse is okay, check for open circuit between battery, ignition switch, and PCM ignition power terminals. If circuits are okay, check for faulty ignition switch.
- Check PCM START signal terminal. On vehicles with manual transmission, depress clutch pedal. On vehicles with automatic transmission, place gearshift lever in Park. Turn ignition switch to START position. Battery voltage should be present only when ignition switch is in START position.
- If voltage is not present, check CRANK fuse or fusible link between ignition switch and PCM START signal terminal. If fuse or fusible link is okay, check for open circuit between ignition switch and PCM START signal terminal, or check for faulty ignition switch.
ENGINE SENSORS & SWITCHES
Note. For additional sensor testing specifications, see appropriate SENSOR OPERATING RANGE CHARTS article.
Manufacturer does not provide testing procedures for many individual systems and components. For sensor and switch testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.
CAMSHAFT POSITION SENSOR
A malfunction in Camshaft Position (CMP) sensor can set DTC P0340. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
CRANKSHAFT POSITION SENSOR
A malfunction in Crankshaft Position (CKP) sensor can set DTC P0335. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
ENGINE COOLANT TEMPERATURE SENSOR
A malfunction in Engine Coolant Temperature (ECT) sensor can set DTCs P0116, P0117 or P0118. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article. An out-of-calibration ECT sensor may not set a DTC. Use the following procedure to test sensor calibration.
Locate and remove ECT sensor from thermostat housing. Using DVOM, measure resistance of ECT sensor at specified temperatures. See ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE table. If resistance is not within specification, replace ECT sensor.
| Temperature - °F (°C) | Ohms |
|---|---|
| 176 (80) | 315 |
| 158 (70) | 435 |
| 140 (60) | 580 |
| 122 (50) | 810 |
| 113 (45) | 940 |
| 104 (40) | 1150 |
| 95 (35) | 1360 |
| 86 (30) | 1600 |
| 77 (25) | 2000 |
| 68 (20) | 2400 |
| 59 (15) | 3000 |
| 50 (10) | 3600 |
| 41 (5) | 4600 |
| 32 (0) | 5700 |
| 23 (-5) | 7400 |
| 14 (-10) | 9800 |
| 5 (-15) | 12,700 |
| 4 (-20) | 16,000 |
| (1) Measure resistance across sensor terminals. | |
| (1) | Measure resistance across sensor terminals. |
ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE (1)
FUEL LEVEL SENSOR
A malfunction in fuel level sensor circuit can set DTCs P0461 and P0463. For testing procedures with DTC set, see appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
FUEL TANK PRESSURE SENSOR
A malfunction in fuel tank pressure sensor circuit can set DTCs P0450 and P0451. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
INTAKE AIR TEMPERATURE SENSOR
A malfunction in Intake Air Temperature (IAT) sensor can set DTCs P0111, P0112 or P0113. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article. An out-of-calibration IAT sensor may not set a DTC. Use the following procedure to test sensor calibration.
Locate and remove IAT sensor from air cleaner assembly. Using DVOM, measure resistance of IAT sensor at specified temperatures. See INTAKE AIR TEMPERATURE SENSOR RESISTANCE table. If resistance is not within specification, replace IAT sensor.
| Temperature - °F (°C) | Ohms |
|---|---|
| 176 (80) | 315 |
| 158 (70) | 435 |
| 140 (60) | 580 |
| 122 (50) | 810 |
| 113 (45) | 940 |
| 104 (40) | 1150 |
| 95 (35) | 1360 |
| 86 (30) | 1600 |
| 77 (25) | 2000 |
| 68 (20) | 2400 |
| 59 (15) | 3000 |
| 50 (10) | 3600 |
| 41 (5) | 4600 |
| 32 (0) | 5700 |
| 23 (-5) | 7400 |
| 14 (-10) | 9800 |
| 5 (-15) | 12,700 |
| 4 (-20) | 16,000 |
| (1) Measure resistance across sensor terminals. | |
| (1) | Measure resistance across sensor terminals. |
INTAKE AIR TEMPERATURE SENSOR RESISTANCE (1)
HEATED OXYGEN SENSOR NO. 1
A malfunction in Heated Oxygen Sensor No. 1 (HO2S 1) circuit can set a related DTC. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article. Use the following procedure to diagnose HO2S 1.
A voltage is produced in response to amount of oxygen in exhaust gases. A lean mixture (high oxygen content) will produce a low voltage of about 100 mV. A rich mixture (low oxygen content) will produce a high voltage of about 900 mV. Voltage reading (activity) should vary above idle.
HEATED OXYGEN SENSOR NO. 2
A malfunction in Heated Oxygen Sensor No. 2 (HO2S 2) circuit can set a related DTC. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article. Use the following procedure to diagnose HO2S 2.
A voltage is produced in response to amount of oxygen in exhaust gases. A lean mixture (high oxygen content) will produce a low voltage of about 100 mV. A rich mixture (low oxygen content) will produce a high voltage of about 900 mV. Unlike HO2S 1, HO2S 2 voltage reading (activity) should seem lazy if TWC is operating properly.
MANIFOLD ABSOLUTE PRESSURE SENSOR
A malfunction in Manifold Absolute Pressure (MAP) sensor circuit can set DTC P1408. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
MASS AIRFLOW SENSOR
A malfunction in Mass Airflow (MAF) sensor circuit can set DTCs P0101, P0102 or P0103. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
THROTTLE POSITION
Note. Throttle Position (TP) sensor is not adjustable. Replace TP sensor as necessary.
A malfunction in TP sensor circuit can set DTCs P0121, P0122 or P0123. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
TRANSMISSION RANGE SWITCH
Disconnect Transmission Range (TR) switch harness connector. Switch is located on side of transmission. Using a DVOM, check for continuity between specified terminals in accordance with shift lever position. See TRANSMISSION RANGE SWITCH CONTINUITY table. (Scheme 20) If continuity is not as specified, replace TR switch.
| Shift Lever Position | Continuity Between Terminals No. |
|---|---|
| "P" | 2 & 3, 6 & 7 |
| "R" | 6 & 8 |
| "N" | 2 & 3, 6 & 10 |
| "D" | 6 & 9 |
| "2" | 4 & 6 |
| "L" | 5 & 6 |
TRANSMISSION RANGE SWITCH CONTINUITY
Scheme 20
VEHICLE SPEED SENSOR
A malfunction in Vehicle Speed sensor (VSS) circuit can set DTC P0500. For testing procedures with DTC set, see appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS.
MODULES, MOTORS, RELAYS & SOLENOIDS
Note. Manufacturer does not provide testing procedures for many individual systems and components. For module, motor, relay and solenoid testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.
FUEL PUMP RELAY
Fuel pump relay is located in underhood fuse/relay block. To test fuel pump relay, see FUEL PUMP RELAY CIRCUIT DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
MAIN RELAY
Main relay is located in underhood fuse/relay block. To test main relay, see MAIN RELAY CIRCUIT DIAGNOSIS under BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
EGR VALVE
A malfunction in EGR system can set DTCs P0400 or P0403. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
EVAP CANISTER PURGE VALVE
See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS.
EVAP CANISTER VENT SOLENOID
See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS.
EVAP TANK PRESSURE CONTROL SOLENOID VACUUM VALVE
See FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS.
IDLE AIR CONTROL VALVE
See IDLE AIR CONTROL VALVE under IDLE CONTROL SYSTEM.
FUEL SYSTEM
Note. For fuel system pressure testing, see appropriate BASIC DIAGNOSTIC PROCEDURES article.
Manufacturer does not provide testing procedures for many individual systems and components. For fuel system testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.
FUEL CONTROL
Note. Retrieve DTCs and perform appropriate DTC test before performing FUEL INJECTOR CIRCUIT DIAGNOSIS. See appropriate SELF-DIAGNOSTICS article. Ensure all mechanical and ignition coil/module circuit malfunctions are repaired before performing fuel injector circuit diagnosis.
See MODULES, MOTORS, RELAYS & SOLENOIDS .
Fuel Pressure Regulator
Fuel pressure regulator is located on fuel rail. Fuel pressure regulator maintains fuel pressure applied to fuel injector at 30-37 psi (2.1-2.6 kg/cm 2 ) at idle. To test fuel pressure regulator, see FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
IDLE CONTROL SYSTEM
Note. For idle control system testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.
IGNITION SYSTEM
Note. For basic ignition checks, see appropriate BASIC DIAGNOSTIC PROCEDURES article.
Electronic Ignition Timing Control
Ignition timing is calculated by PCM based on current engine status. PCM provides 3 modes of ignition timing control. Each ignition timing mode provides the most suitable spark advance for optimal engine performance. The 3 modes are as follows
- Initial Timing Control (At Engine Start) Initial Timing Control ignition advance provides better starting performance during start-up when engine speed is less than 500 RPM. PCM sets initial ignition timing advance to 5 degrees BTDC.
- Basic Timing Control (After Engine Start) After engine is running, ignition timing advance is determined by combining Basic Timing Control and Compensating Timing Control. Basic Timing Control ignition advance is based on engine coolant temperature, engine speed and intake air volume. Ignition timing advance value calculated from ECT sensor, CMP sensor and MAF sensor input is added to the 5 degrees BTDC initial advance and then modified by the Compensating Timing Control value.
- Compensating Timing Control Compensating Timing Control is added to Basic Timing Control value and varies according to engine and vehicle conditions. Conditions utilized for determining Compensating Timing Control value, are engine coolant temperature, intake air temperature and engine idling demands.
PCM cannot operate ignition system without engine speed signal from camshaft position sensor. PCM controls ignition timing by controlling ignition coils. Ignition timing is controlled by PCM and is adjustable. See IGNITION TIMING in appropriate ON-VEHICLE ADJUSTMENTS article.
EMISSION SYSTEMS & SUB-SYSTEMS
Note. For emission and subsystem testing not listed, perform related DTC testing procedure. See appropriate SELF-DIAGNOSTICS article.
EXHAUST GAS RECIRCULATION
A malfunction in EGR system can set a related DTC. For testing procedures with DTC set, see appropriate SELF-DIAGNOSTICS article.
FUEL EVAPORATION
| WARNING | DO NOT suck air through Evaporative Emission (EVAP) system hoses or components. Fuel vapor inside EVAP canister and hoses is harmful. |
Required Service
PCV system may require service for obstructed PCV valve or hose if any of the following conditions exist
- Excessive exhaust emissions.
- High crankcase pressure.
- Oil leaks.
- Oil in air cleaner.
- Oil consumption.
- Rough idle.
- Sludge in engine.
- Stalling or low idle speed.
A leaking PCV valve or hose could cause
- Excessive exhaust emissions.
- Incorrect crankcase pressure.
- High idle speed.
- Rough idle.
- Stalling.
If engine idles roughly, check for clogged PCV valve, or plugged or broken hoses. Check PCV valve application to ensure correct valve is fitted. Replace PCV valve as necessary.
Checking PCV Valve Function
Note. An engine must be sealed for PCV system to function as designed. If leakage, sludging or dilution of oil is noted and PCV system is functioning properly, check engine for cause and repair as required to ensure PCV system will continue to function properly.
- Disconnect PCV valve vacuum hose from cylinder head cover. Run engine at idle. Place thumb over end of PCV valve vacuum hose to check for vacuum. If vacuum does not exist, remove hose and check for obstruction. If PCV valve vacuum hose is okay, go to next step.
- Turn ignition off. Remove PCV valve. Visually inspect valve for varnish or deposits which may cause PCV valve operation to be sticky, restricted, or cause incomplete seating of valve. Shake valve and listen for rattle of check valve inside. If a clear rattle is not heard, replace PCV valve.
MISCELLANEOUS CONTROLS
Note. Although some controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.
TRANSMISSION
Note. Computerized transmission controls are also covered in greater detail in appropriate ELECTRONIC CONTROLS article in AUTOMATIC TRANSMISSIONS. For component circuit identification, see WIRING DIAGRAMS article.