Engine Control System Testing & Engine Component Testing: Overview Pontiac Bonneville X

MODEL IDENTIFICATION

Vehicle model is identified by fourth character of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

MODEL IDENTIFICATION

Description

The boost control solenoid is a normally open valve. Under most conditions, the Powertrain Control Module (PCM) commands the boost control solenoid to operate at 100 percent duty cycle, which closes the solenoid valve to allow the system to boost. This is achieved by allowing manifold vacuum to reach the top port of the bypass valve actuator through the inlet vacuum signal hose. With the boost control solenoid closed, vacuum from the boost source hose can not reach the lower port of the bypass valve actuator to disable boost. However, if reverse gear is selected, the PCM detects deceleration, engine temperature is extremely high, or drive train abuse is detected, then reduced boost pressure is desired. Under these conditions the PCM commands the boost control solenoid to operate at 0 percent duty cycle, which opens the solenoid valve and allows vacuum to pass from the boost source hose, through the boost control solenoid and boost signal hose, to the bypass valve actuator lower port. This disables boost by opening the bypass valve. With the bypass valve open, boost pressure is reduced by recirculating intake air back through the supercharger inlet.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold which gives an indication of the engine load. The MAP sensor has the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low signal voltage. With high MAP such as ignition ON, with the engine OFF or Wide Open Throttle (WOT), the PCM should detect a high signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

Test Description

The number below refers to the step number in the diagnostic procedures.

1. 2 This step tests the MAP sensor's ability to correctly indicate BARO. The BARO varies with altitude and atmospheric conditions. 103 kPa is the approximate BARO displayed by the MAP sensor at or near sea level.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold which gives an indication of the engine load. The MAP sensor has the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low MAP such as during idle or deceleration, the PCM should detect a low signal voltage. With high MAP such as ignition ON, with the engine OFF or Wide Open Throttle (WOT), the PCM should detect a high signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the Barometric (BARO) pressure when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

The number below refers to the step number in the diagnostic procedures.

1. 2 This step tests the MAP sensor's ability to correctly indicate BARO. The BARO varies with altitude and atmospheric conditions. 103 kPa is the approximate BARO displayed by the MAP sensor at or near sea level.

The scan tool first energizes the fuel pump and then the injectors for a precise amount of time allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 The Engine Coolant Temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.
2. 4 The fuel pressure should be within the specified range. See «FUEL PRESSURE SPECIFICATIONS (EXCEPT SATURN)»(ref-150423-S22117630242002111200000) table or «FUEL PRESSURE SPECIFICATIONS (SATURN)»(ref-150423-S18200120992002111200000) table. If the fuel pressure is not within the specified range, see appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.
3. 5 The fuel pressure should reach a steady value. See appropriate FUEL SYSTEM PRESSURE TEST article under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES - CARS - EXCEPT PRIZM article.
4. 6 If the pressure drop value for each fuel injector is within 1.5 psi of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.

The Powertrain Control Module (PCM) enables the appropriate fuel injector on the intake stroke for each cylinder. A voltage is supplied directly to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high, or low, will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests each fuel injector resistance within a specific temperature range. If any of the fuel injectors display a resistance outside of the specified value, replace the fuel injector.
2. 4 This step determines if all of the fuel injectors are within 3 ohms of each other. If the highest resistance value is within 3 ohms of the lowest resistance value, then all of the fuel injector coil windings are okay.
3. 5 This step determines which fuel injector is faulty. After subtracting the highest and lowest resistance values from the average value, replace the fuel injector that has the greatest resistance difference from the average.

Lock-off relay is energized whenever Powertrain Control Module (PCM) supplies power to gasoline fuel pump circuit. PCM supplies power to gasoline fuel pump circuit for approximately 2 seconds at every ignition on cycle and whenever 7X reference pulses indicate engine is cranking or running. When energized, lock-off relay supplies power to high and low pressure lock-off solenoids. At initial ignition on cycle, PCM energizes gasoline fuel pump relay, supplying power to fuel pump power circuit for a two second prime pulse. When prime pulse is supplied to fuel pump power circuit, lock-off relay is energized.

When engine is started, PCM energizes gasoline fuel pump relay, supplying power to fuel pump power circuit. PCM will supply power to fuel pump power circuit, regardless of fuel system that in operation, as long as crankshaft pulses are monitored (engine is running).

High and Low Pressure Lock-Off (HPL and LPL) solenoids are energized by Alternate Fuel Engine Control Module (AF ECM) when vehicle is operating in CNG mode. At initial ignition on request, AF ECM will close the HPL solenoid control circuit driver (completing circuit path to ground) for a one second CNG prime pulse. Prime pulse occurs at same time as gasoline fuel pump prime pulse occurs. This ensures lock-off relay will be energized and supplying power to lock-off solenoids at the same time AF ECM closes driver and supplies ground path. When engine is cranking or running, AF ECM closes BOTH lock-off solenoid control circuit drivers, allowing engine to operate on CNG.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The System Check must be performed before proceeding with this diagnostic test. Failure to perform the System Check will result in misdiagnosis.
2. 2 This step checks the battery voltage supply from the lock-off relay to the LPL. The lock-off relay is energized regardless of which fuel system is operating the vehicle.
3. 3 This step checks the AF ECM and the Low Pressure Lock-Off Solenoid Control circuit for proper operation. The test lamp should illuminate for a few seconds then turn OFF as the engine cannot start on CNG with the LPL disconnected.
4. 4 This step checks the battery voltage supply from the lock-off relay to the HPL. The lock-off relay is energized regardless of which fuel system is operating the vehicle.
5. 5 This step check the AF ECM and the High Pressure Lock-Off Solenoid Control circuit for proper operation. The test lamp should illuminate for a few seconds then turn OFF as the AF ECM opens the HPL for system priming prior to cranking the engine.
6. 6 This step checks for proper battery voltage output from the lock-off relay.
7. 7 This step checks for proper relay coil positive voltage and ground supply.
8. 8 This step checks for proper battery voltage supply from the CNG fuse (20-amp) circuit to the lock-off relay. If the test lamp fails to illuminate the failure can only exist between the relay and the circuit splice. For example: a blown fuse would cause a lack of power to the AF ECM causing no scan tool communication in which the OBD System Check would have directed you to a different diagnostic procedure.
9. 9 This step checks for proper positive voltage supply from the gasoline fuel pump circuit to the lock-off relay.

Alternate Fuel Engine Control Module (AF ECM) supplies power to AF fuel pump relay coil when engine starts and runs on CNG. AF fuel pump relay allows AF ECM to turn off gasoline fuel pump and supply a voltage source for lock-off relay. At initial ignition on, AF fuel pump relay is not energized by AF ECM. Powertrain Control Module (PCM) energizes gasoline fuel pump relay, supplying power to fuel pump power circuit for 2 second prime pulse. When prime pulse is supplied to fuel pump power circuit, lock-off relay is energized and gasoline fuel pump receives 2 second prime pulse power. When the engine is started, PCM energizes gasoline fuel pump relay, supplying power to fuel pump power circuit. When engine is operating on CNG, AF ECM energizes AF fuel pump relay, turning off the gasoline fuel pump. Lock-off relay continues to be energized by gasoline fuel pump relay.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The Diagnostic System Check - Engine Controls must be performed before proceeding with this diagnostic test. Failure to perform the OBD System Check will result in misdiagnosis.
2. 2 This step tests if the engine will start and run. A failure that causes the engine to not start on either fuel can be isolated to the CNG harness or a base vehicle problem such as a malfunctioning gasoline fuel pump relay.
3. 3 This step tests the gasoline control modules ability to supply power to the gasoline fuel pump circuit.
4. 5 This step tests for voltage through the AF fuel pump relay. With the ignition ON and the engine OFF the AF ECM does not energize the AF fuel pump relay allowing voltage to flow through the relay and energize the gasoline fuel pump.
5. 6 This step tests the AF ECMs ability to energize the AF fuel pump relay and disable the gasoline fuel pump during CNG operation.
6. 7 This step tests for stuck AF fuel pump relay contacts or a shorted AF Fuel Pump Relay control circuit.
7. 10 If the engine did not operate on gasoline during the Diagnostic System Check - Engine Controls but now operates on gasoline inspect for intermittent terminal contact or a AF fuel pump relay with sticking contacts that may have been disturbed during testing.
8. 11 This step tests if the CNG harness is the cause of the no-start on gasoline.
9. 15 If the Fuel Pump Power circuit tests okay there is a base vehicle problem that is causing the no-start condition.

Alternative Fuel Engine Control Module (AF ECM) controls fuel system while vehicle is operating on alternative fuel. AF ECM receives signals from various engine sensors and determines correct amount of fuel required by engine. Full tank can contain fuel at 3600 psi (24,820 kPa). A High Pressure Lock-Off (HPL) solenoid in the tank and Low Pressure Lock-Off (LPL) solenoid in fuel line prevent fuel flow. AF ECM commands the HPL ONLY open for one second at every ignition ON for a CNG prime pulse. CNG prime pulse is performed charge fuel line and allow Fuel Pressure Sensor (FPS) to monitor amount of fuel pressure in tank. AF ECM commands both HPL and LPL open when engine RPM indicates engine is cranking or running on CNG.

This fuel delivery system uses 3 different pressure stages to lower fuel pressure from tank pressure down to a delivery pressure which is slightly above atmospheric pressure.

1. High Pressure (Tank) Stage - When AF ECM commands HPL open, fuel begins to flow through High Pressure Regulator (HPR). HPR reduces fuel pressure to 115-220 psi (793-1517 kPa). Outlet of HPR is intermediate pressure stage.
2. Intermediate Pressure Stage With pressure 115-220 psi (793-1517 kPa), fuel exiting HPR flows through intermediate fuel line to Low Pressure Lock-Off (LPL) solenoid. LPL is controlled by AF ECM. Fuel flows out of LPL through another portion of the intermediate fuel line and into Low Pressure Regulator (LPR). Inlet of LPR is the low pressure stage.
3. Low Pressure Stage Low pressure regulator is a 2 stage regulator. Fuel enters LPR at intermediate stage pressure of 115-220 psi (793-1517 kPa). Primary stage of LPR operation reduces fuel pressure down to 4-6 psi (28-41 kPa). Fuel pressure is then again reduced in the secondary stage of LPR, down to 2-5 in. H 2 0 (5.1-12.7 cm). Fuel exits LPR and flows through low pressure hose and into Gas Mass Sensor/Mixture Control Valve (GMS/MCV).

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests the fuel pressure output of the High Pressure Regulator (HPR).
2. 5 This step tests the fuel pressure output of the Primary Stage of the Low Pressure Regulator (LPR).
3. 6 CNG fuel may contain small amounts of fill station compressor oil. As the CNG fuel pressure drops in the LPR secondary chamber this oil separates from the CNG fuel and collects in the secondary chamber. Allow the oil to drain as this condition is normal and no repair is required. This step tests the fuel pressure output of the Secondary Stage of the Low Pressure Regulator (LPR).
4. 8 This step tests for the sound of a functioning LPL. A circuit failure to solenoid should set a DTC.
5. 9 This step tests for the sound of a functioning HPL. A circuit failure to solenoid should set a DTC.
6. 10 This step tests for a restricted High Pressure Regulator (HPR) filter. If a restricted HPR filter is found also inspect the fill valve filter for contamination, damage or restriction.
7. 11 This step inspects for a closed manual lock-down screw.
8. 12 This step inspects for damage to the fuel line between the HPL and the LPR.
9. 19 This step tests for a leaking LPL. A leaking LPL would allow CNG fuel to enter the engine after the ignition has been turned OFF. The leaking LPL could cause a hard or no-start condition during the next ignition cycle. A leaking LPL would cause the gauge to indicate fuel pressure for up to several minutes after the ignition has been turned OFF.
10. 20 This step tests for proper operation of the system after repairs are complete.

Alternate Fuel Engine Control Module (AF ECM) and Powertrain Control Module (PCM) are connected by the Alternative Fuels Operation (AFO) Enable circuit. For engine to switch-over to CNG operation, PCM must be commanded to disable gasoline fuel injectors, switch to a different ignition spark calibration and disable some PCM DTCs. AF ECM performs switch-over command by grounding AFO enable circuit when CNG operation is desired.

This vehicles primary fuel source is compressed natural gas (CNG). Vehicle will only switch-over to gasoline operation if one of the following conditions is present

1. Fuel Tank Pressure (FTP) sensor indicates CNG tank is empty.
2. A wide-open Mixture Control Valve (MCV) is detected.
3. System fault is detected by control module (AF ECM or PCM).
4. Manual shut-off valve is closed.
5. Engine crank time exceeds 8 seconds.
6. On every 100th start and also when coolant temperature is less than 10°F (-12°C), vehicle will start and run briefly on gasoline. A switch-over to CNG will occur only during a decel condition.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The System Check must be performed before proceeding with this diagnostic procedure. Failure to perform the System Check will result in misdiagnosis.
2. 2 This step inspects if the AF ECM has commanded the gasoline control module, using the AFO Enable circuit, to start on CNG. The AFO Signal Command parameter is the commanded state of the AFO Enable circuit from the AF ECM. The AFO Signal parameter is the monitored state of the AFO Enable circuit from the GASOLINE control module (PCM).
3. 3 This step inspects if the FIL is illuminated during CNG operation. The FIL should illuminate only during gasoline operation.
4. 5 This step inspects if the FTP sensor is monitoring adequate fuel tank pressure for the vehicle to start on CNG.
5. 6 This step tests the ability of the AF ECM to command Alternative Fuels Operation (AFO) and the gasoline control modules ability to monitor the command.
6. 7 This step indicates all the possibilities that cause a switch-over to gasoline operation.
7. 8 This step inspects the ignition system of the vehicle for proper operation. A vehicle that operates correctly on gasoline but not on CNG may have a faulty ignition system.
8. 9 Performing the Fuel System Diagnosis checks the basic AF fuel system for proper pressures and lock-off solenoid operation.
9. 10 A fuel system that is unable to retain fuel pressure after the ignition is turned OFF may cause an Unwanted Switch to Gasoline. The AF ECM commands the HPL open for about 1 second every time the ignition is turned ON. If the fuel line system leaks during ignition OFF the next ignition ON prime pulse will usually recharge the fuel lines and the FTP sensor. A sluggish HPL may not open enough during the 1 second prime pulse but will open when commanded with the scan tool.
10. 11 This step tests for proper fuel tank pressure sensor operation.
11. 12 This step tests for an inoperative HPL. After connecting to a CNG dispensing station the CNG fuel lines, the FTP sensor and the fuel tank will be charged by the station. The CNG fuel pressure in the lines and the FTP sensor will quickly drop if the engine is operating on CNG but the HPL fails to open.
12. 13 This step tests for proper operation of the AFO Enable circuit and the gasoline control module.
13. 15 This step tests for a leaking fuel system with a sluggish HPL.

The engine idle speed is controlled by the Idle Air Control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The valve consists of a movable pintle, driven by a gear attached to a two phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has two separate windings that are called coils. Each coil is fed by two circuits from the Powertrain Control Module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed Diagnostic Trouble Code (DTC) may set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 This test determines the ability of the PCM and IAC valve circuits to control the IAC valve.
2. 7 This test determines the ability of the PCM to provide the IAC valve circuits with a ground. On a normally operating system, the test lamp should not flash while the IAC counts are incrementing.

Ignition relay is positive voltage supply source for Gas Mass Sensor/Mixture Control Valve (GMS/MCV) and fuel gauge select switch. Ignition relay coil is energized when ignition switch is turned to Run or Start positions. Ignition relay switch contact is supplied voltage at all times.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 The System Check must be performed before proceeding with this diagnostic test. Failure to perform the System Check will result in misdiagnosis.
2. 3 This step tests the AF ECM fuses for opens and also tests the voltage supply to the fuses.
3. 5 This step tests the battery positive and switched ignition voltage circuits to the AF ECM.
4. 6 This step tests the AF ECM ground circuits.
5. 7 This step inspects for proper operation of the FIL. If the FIL illuminates then the ignition relay is ON.
6. 9 This step inspects the ignition relays ability to turn OFF.
7. 12 This step tests the Ignition Relay coils ground circuit. If the test lamp illuminates then the Ignition relay must be faulty.
8. 13 This step indicates the components or circuits that may have caused a fuse to blow. Some components may require they be turned ON in order to blow the fuse. An example would be depressing the fuel gauge select switch in order to test the select switch circuit for a short.

The numbers below refer to the step numbers on the diagnostic table.

7. An ignition coil, boots, or spark plugs may misfire only when moisture is present. Although difficult to test on this engine, selectively wetting down parts of the system and monitoring for misfire may isolate an intermittent condition. If moisture is present in the spark plug/ignition coil cavity of the cam cover, inspect the perimeter seal for damage. Repair any tears in the perimeter seal with an RTV sealant.

8. The J 26792 Spark Tester (ST 125) places a higher load on the secondary ignition than a normal spark plug.

13. Use the correct adaptor harness when connecting the Ignition Module Tester. Using an adaptor harness for a different engine application will result in incorrect tool operation.

The green Power LED should come on any time the ignition module tester is connected and the ignition switch is in the run position. This LED indicates that J 43298 Ignition Module Tester is receiving adequate power and ground to perform the test. The Test button is used as an LED check for the 4 red LEDs. In order to use this function, connect the tool, turn the ignition switch to run, then momentarily press the Test button. All 4 red LEDs should come on brightly. Then crank the vehicle. If the 4 red LEDs flash, this confirms proper operation of the primary ignition system, including the PCM, the wiring, the connections, and the ignition control module (ICM). The ignition module tester may get hot during actual testing. This is because the tester is attempting to simulate the load of the ignition coils primary windings.

If the LEDs flash, the module output drivers are operating. If one or more LEDs are inoperative, and no individual IC Circuit (DTC P0351-P0358) Group, or IC Circuit Group (DTC P1359 and/or P1360) DTCs are set, replace the module.

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

The fuel tank leak test is used to locate any fuel or fuel vapor escaping the fuel tank area. Fuel vapors escaping above the fuel level will be detected when the Evaporative (EVAP) emission diagnostics complete one test cycle. The Malfunction Indicator Lamp (MIL) will illuminate after the EVAP diagnostics complete two test cycles.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 Perform this procedure in order to determine that no EVAP diagnostic DTC is present.
2. 3 This test is to locate fuel leakage in the fuel lines.
3. 4 This tests for fuel leaks below the fuel tank fuel level.
4. 5 This test is to locate fuel vapors escaping above the fuel level in the fuel tank.