Engine Control System & Engine Component Tests - 4.3L: Other Oldsmobile Bravada II

AIR INDUCTION SYSTEMS

Note. Manufacturer does not supply many individual component tests. For component tests not listed, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. See TROUBLE CODE DEFINITION table.

CONTROL UNIT

Note. To identify circuits referenced in the following ground and power tests, use wiring diagram in WIRING DIAGRAMS - 4.3L article.

Ground Circuits

1. Using an ohmmeter, check for continuity to ground on PCM/VCM ground terminals. See «POWERTRAIN CONTROL MODULE (PCM)»(ref-131391-S37823730892001121900000) table. Resistance should be zero ohms. If not, repair open to ground.
2. Connect negative lead of a voltmeter to a good ground. Backprobe positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is more than one volt, check for open, short to voltage, corrosion or loose connection on ground circuit.

Power Circuits

1. Using a voltmeter, check for battery voltage between PCM/VCM continuous power terminal(s) and ground. See «POWERTRAIN CONTROL MODULE (PCM)»(ref-131391-S37823730892001121900000) table. If battery voltage is not present, check for blown fuse or open fusible link. If okay, check for open in wire between PCM/VCM terminal and power source.
2. Turn ignition switch to RUN position. Using a voltmeter, check for battery voltage between PCM/VCM ignition power terminals and ground. If battery voltage is not present, check IGN fuse. If fuse is okay, check for an open in wire between battery and ignition switch, and between ignition switch and PCM/VCM terminal. If okay, check for a defective ignition switch.
3. Connect voltmeter between ground and PCM/VCM starter (crank) signal terminal. On vehicles with manual transmission/transaxle, depress clutch pedal. On vehicles with automatic transmission/transaxle, position gear shift lever in Park. On all vehicles, turn ignition switch to START position. Battery voltage should be present ONLY when ignition switch is in START position.
4. If voltage is not present, check CRANK fuse or fusible link between ignition switch and PCM/VCM terminal. If fuse or fusible link is okay, check for an open in wire between ignition switch and PCM/VCM terminal, or check for a defective ignition switch.

ENGINE SENSORS & SWITCHES

Note. Manufacturer does not supply many individual component tests. For component tests not listed, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. See TROUBLE CODE DEFINITION table.

Engine Coolant Temperature (ECT) Sensor

If an ECT sensor-related code is present, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test sensor calibration. Disconnect ECT sensor harness connector. Measure resistance between ECT sensor terminals. Sensor resistance should be as specified. See ECT SENSOR RESISTANCE VALUES table. Resistance should be high when engine is cold and drop as engine warms. With vehicle sitting overnight, IAT sensor and coolant sensor should have close to the same resistance reading.

ECT SENSOR RESISTANCE VALUES

Note. Intake Air Temperature (IAT) sensor may also be referred to as Manifold Air Temperature (MAT) sensor.

Intake Air Temperature (IAT) Sensor

If an IAT sensor-related code is present, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. An out-of-calibration sensor may not set a trouble code. Use following procedure to test calibration. Disconnect IAT sensor harness connector. Measure resistance between IAT sensor terminals. Sensor resistance should be as specified. See IAT SENSOR RESISTANCE VALUES table. Resistance should be high when air temperature is cold and drop as air temperature warms. With vehicle sitting overnight, IAT sensor and coolant sensor should have close to the same resistance reading.

IAT SENSOR RESISTANCE VALUES

Scheme 7

Note. Ensure oil is okay before performing engine oil level sensor/switch diagnosis.

MODULES, MOTORS, RELAYS & SOLENOIDS

Note. Manufacturer does not supply many individual component tests. For component tests not listed, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. See TROUBLE CODE DEFINITION table.

A/C Clutch Relay

See A/C SYSTEM GENERAL SERVICING article in AIR CONDITIONING & HEAT section.

Fuel Pump Relay

See BASIC TESTING - 4.3L article.

Canister Purge Solenoid

See EMISSION SYSTEMS & SUB-SYSTEMS .

Idle Air Control (IAC) Valve

See FUEL SYSTEM .

FUEL SYSTEM

Note. Manufacturer does not supply many individual component tests. For component tests not listed, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. See TROUBLE CODE DEFINITION table.

FUEL DELIVERY

Note. For fuel system pressure testing, see BASIC TESTING - 4.3L article.

Fuel Pressure Regulator (CSI)

Fuel pressure regulator is mechanically controlled by internal spring pressure. Regulator is adjusted at factory and is not serviceable. If fuel pressure is too low, check for restricted delivery line. Also, check fuel pump pressure and volume. If fuel pressure is too high, check for restricted fuel tank return line or fuel filter. If no faults are found and pressure is too high or too low, replace fuel pressure regulator.

Fuel Pressure Regulator (SFI)

Fuel pressure regulator is a vacuum-controlled diaphragm type, which uses manifold vacuum to modify fuel pressure to compensate for engine load fuel requirements. Connect fuel pressure gauge to fuel pressure service port. Start engine and note fuel pressure. Disconnect vacuum hose from fuel pressure regulator. Fuel pressure should increase 4-10 psi (.28-.70 kg/cm 2 ). If pressure does not increase 4-10 psi (.28-.70 kg/cm 2 ), check for presence of manifold vacuum at signal line. If vacuum is not present, check for kinked, cut or split vacuum hose or plugged throttle body vacuum port. If vacuum is present and no pressure change occurs, replace fuel pressure regulator.

Fuel Pump Oil Pressure Switch (Back-Up Circuit)

To test fuel pump oil pressure switch (fuel pump back-up circuit), start engine. With engine running, disconnect fuel pump relay. If engine stalls, fuel pump oil pressure switch is faulty. If vehicle continues to run, switch is okay.

FUEL CONTROL

Note. If injectors are dirty, they should be cleaned using approved injector cleaning procedure before performing INJECTOR BALANCE TEST.

IGNITION SYSTEM

Note. Manufacturer does not supply many individual component tests. For component tests not listed, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. See TROUBLE CODE DEFINITION table.

Note. For basic ignition system checks, see BASIC TESTING - 4.3L article.

Ignition Control Circuit

An open or short to ground in Ignition Control (IC) or by-pass circuit will cause PCM/VCM to turn on Malfunction Indicator Light (MIL) and confirm fault by setting a related trouble code. See TESTS W/CODES - 4.3L article.

Knock Sensor Circuit (Models Using External Spark Controller Module)

1. An open or short circuit on IC module control wire to PCM/VCM will cause a loss of 12-volt IC module signal. This will cause PCM/VCM to fully retard ignition timing.
2. If a scan tool is available, connect tester to Data Link Connector (DLC). Using a metal object, tap on engine next to knock sensor and note knock parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, backprobe PCM/VCM knock sensor signal terminal with a DVOM. With engine idling, 8-12 volts should be present at this terminal. Using a metal object, tap on engine close to knock sensor. Voltage signal at PCM/VCM terminal should drop to zero volts, and return to original voltage when knock signal ceases.
4. If voltage signal does not respond as described, check knock sensor-to-module-signal. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur.

Knock Sensor Circuit (Models Using Knock Sensor With Internal Spark Controller Module)

1. An open or short circuit on knock sensor wire to PCM/VCM will set a related trouble code. A false detonation signal will not cause PCM/VCM to set a code.
2. If a scan tool is available, connect it to Data Link Connector (DLC). Tap on engine next to knock sensor and note "knock" parameter. Knock should be indicated on scan tool.
3. If a scan tool is not available, connect tachometer to engine. Start engine and hold RPM above idle. Using a metal object, tap on engine close to knock sensor. A noticeable decrease in engine RPM should occur. If no RPM decrease occurred, check knock sensor to PCM/VCM circuit.
4. On vehicles equipped with automatic transmission, it may be necessary to place transmission in Drive for timing change to occur.

EMISSION SYSTEMS & SUB-SYSTEMS

Note. Manufacturer does not supply many individual component tests. For component test not listed, perform appropriate DTC test. See TESTS W/CODES - 4.3L article. See TROUBLE CODE DEFINITION table.

Exhaust Gas Recirculation (EGR) System Check

1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in «TESTS W/CODES - 4.3L»(ref-33422) article.
2. Remove heated oxygen sensor. Install exhaust backpressure tester in place of oxygen sensor. Start engine and let idle. If pressure reading is not 1.25 psi or greater, go to next step. If pressure reading is within specification, go to step 4).
3. Increase engine speed to 2000 RPM. If pressure reading is greater than 3 psi (.2 kg/cm 2 ), go to next step. If pressure reading is not within specification, go to step 6).
4. Check exhaust system for crushed pipe, internal muffler damage or heat distress. If problem does not exist, go to next step. If problem exists, repair as necessary and go to step 6).
5. Replace catalytic converter and go to next step.
6. Operate vehicle within conditions under which original symptom was noted. If system operate properly, system is okay at this time. If system does not operate properly, go to step 2).

POSITIVE CRANKCASE VENTILATION

Required Service - The PCV system may require service for obstructions if any of the following conditions exist

1. Rough Idle
2. Stalling Or Low Idle Speed
3. Oil Leaks
4. Oil In Air Cleaner
5. Sludge In Engine

A leaking PCV valve or hose could cause

1. Rough Idle
2. Stalling
3. High Idle Speed

If engine idles rough, check for clogged PCV valve and for plugged or broken PCV hoses before adjusting idle. Check for correct PCV valve application. Replace PCV valve if required.

Checking PCV Valve Function

1. Remove PCV valve from rocker cover. Start engine and let idle. Place thumb over open end of valve to check for vacuum. If there is no vacuum at valve, check for obstruction in manifold port, hoses or PCV valve. Repair or replace as necessary.
2. Turn ignition switch to LOCK position. Remove PCV valve. Shake valve and listen for rattle of check valve inside PCV valve. If a clear rattle is not heard, replace PCV valve.
3. Visually inspect valve for varnish or deposits that may make PCV valve sticky, restricted or incompletely seated. Replace if necessary.
4. 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.
5. Since an engine operating without any crankcase ventilation can be damaged, it is important to replace PCV valve and air cleaner breather at regular intervals (at least every 30,000 miles). Check all hoses and clamps for failure or deterioration.

MISCELLANEOUS PCM/VCM CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

Note. Manufacturer does not supply many individual component tests. For component tests that are not listed, perform appropriate DTC test. See TROUBLE CODE DEFINITION table in TESTS W/CODES - 4.3L article.

TRANSMISSION

Note. To identify circuits referenced in the following tests, use appropriate wiring diagram in WIRING DIAGRAMS - 4.3L article. PCM/VCM transmission controls are also covered in greater detail in TRANSMISSION SERVICING A/T article in AUTOMATIC TRANS SERVICE section or TRANSMISSION SERVICING M/T article in MANUAL TRANS SERVICE section REPAIR manual.

Converter Lock-Up Signal At Transmission

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Disconnect converter clutch connector at transmission. Connect a test light across converter clutch harness terminals. Start engine and place transmission in Drive. Accelerate vehicle to 45 MPH and note test light.
3. If test light is not on, check solenoid power supply wire of harness for open or short to ground. Check ground circuit for open between harness connector and PCM/VCM. If harness is okay, see CONVERTER LOCK-UP SIGNAL FROM PCM/VCM.

Converter Lock-Up Signal From PCM/VCM

1. Warm engine to operating temperature. Raise vehicle and support drive wheels. Support suspension where necessary to prevent damage to drive axles.
2. Connect a test light to battery voltage. Touch TCC control driver terminal with test light. Accelerate vehicle to 45 MPH and note test light. If test light does not illuminate, problem is a faulty PCM/VCM connector or PCM/VCM.

Shift Light (Manual Transmission)

1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK in «TESTS W/CODES - 4.3L»(ref-33422) article.
2. Turn ignition switch to LOCK position. Connect scan tool to data link connector. Turn ignition switch to RUN position. Using scan tool, command shift light on. If shift light does not illuminate, go to next step. If shift light illuminates, go to step 4).
3. Turn ignition switch to LOCK position. Disconnect PCM harness connector that contains shift light circuit. Turn ignition switch to RUN position. Using a fused jumper wire, ground shift light control circuit (Tan/Black wire) at PCM harness connector. If shift light illuminates when grounded, go to step 5). If shift light does not illuminate, go to step 6).
4. Using scan tool, command shift light off then on. If shift light operates as expected, system is okay at this time. If shift light does not operate as expected, go to step 8).
5. Check for poor connection at PCM. If poor connection exists, go to step 7). If poor connection does not exist, go to step 10).
6. Repair open in shift light control circuit and go to step 11).
7. Repair poor connection as necessary and go to step 11).
8. Turn ignition switch to LOCK position. Disconnect PCM harness connector that contains shift light circuit. Turn ignition switch to RUN position. If shift light illuminates, go to next step. If shift light does not illuminate, go to step 10).
9. Repair short to ground in shift light control circuit (Tan/Black wire) between PCM and instrument cluster. After repair is complete, go to step 11).
10. Replace PCM. Program PCM, perform VTD password relearn procedure and perform crankshaft variation learn procedure. See «COMPUTER RELEARN PROCEDURES»(ref-33335) in GENERAL INFORMATION article. After repair is complete, go to next step.
11. Start engine and let idle until normal operating temperature is obtained. Select DTC FAILED THIS IGNITION on scan tool. If DTCs do not exist, system is okay at this time. If DTCs exist, perform appropriate DTC test. See «TESTS W/CODES - 4.3L»(ref-33422) article.

Compressor Clutch Controls (RWD Trucks)

The A/C clutch relay is controlled by PCM. The PCM improves idle quality by delaying compressor clutch engagement until idle speed is increased, or disengages compressor clutch when idle speed is too low. Compressor clutch is cycled by PCM. The PCM smooths cycling of compressor clutch by adding fuel the instant compressor clutch is applied.

ELECTRIC COOLING FAN CONTROL

Note. For electric cooling fan circuit testing, see ELECTRIC COOLING FAN article in ENGINE COOLING section.

All FWD and some RWD vehicles use an electric cooling fan. The electric cooling fan is used for radiator and A/C condenser cooling. Cooling fan operates when A/C is on and when engine coolant temperature exceeds a specific value. One or more cooling fan relays may be used. Some RWD trucks are equipped with an auxiliary electric cooling fan.