Engine Controls - 4.3L (Introduction): Other Chevrolet Silverado 3500

Temperature vs Resistance

Temperature vs Resistance

Altitude vs Barometric Pressure

Altitude vs Barometric Pressure

CKP System Variation Learn Procedure

1. Install a scan tool.
2. Monitor the powertrain control module (PCM) for DTCs with a scan tool. If other DTCs are set, except DTC P0315, refer to «Diagnostic Trouble Code (DTC) List»(ref-184132-S03934914592005082200000) for the applicable DTC that set.
3. Select the crankshaft position variation learn procedure with a scan tool.
4. The scan tool instructs you to perform the following: Accelerate to wide open throttle (WOT). Release throttle when fuel cut-off occurs. Engine should not accelerate beyond calibrated RPM value. Release throttle immediately if value is exceeded. Block drive wheels. Set parking brake. DO NOT apply brake pedal. Cycle ignition from OFF to ON. Apply and hold brake pedal. Start and idle engine. Turn A/C OFF. Vehicle must remain in Park or Neutral. The scan tool monitors certain component signals to determine if all the conditions are met to continue with the procedure. The scan tool only displays the condition that inhibits the procedure. The scan tool monitors the following components: Crankshaft position (CKP) sensors activity-If there is a CKP sensor condition, refer to the applicable DTC that set. Camshaft position (CMP) sensor activity-If there is a CMP sensor condition, refer to the applicable DTC that set. Engine coolant temperature (ECT)-If the engine coolant temperature is not warm enough, idle the engine until the engine coolant temperature reaches the correct temperature.
5. Enable the crankshaft position system variation learn procedure with the scan tool.
6. Accelerate to WOT.
7. Release when the fuel cut-off occurs.
8. The scan tool displays Learn Status: Learned this ignition. If the scan tool indicates that DTC P0315 ran and passed, the CKP variation learn procedure is complete. If the scan tool indicates DTC P0315 failed or did not run, refer to «DTC P0315»(ref-184243-S36198199912005082200000) . If any other DTCs set, refer to «Diagnostic Trouble Code (DTC) List»(ref-184132-S03934914592005082200000) for the applicable DTC that set.
9. Turn OFF the ignition for 30 seconds after the learn procedure is completed successfully.
10. The CKP system variation learn procedure is also required when the following service procedures have been performed, regardless of whether DTC P0315 is set. An engine replacement A PCM replacement A harmonic balancer replacement A CKP sensor replacement Any engine repairs which disturb the CKP sensor relationship

Throttle Body Cleaning Procedure

1. Remove the air cleaner outlet duct. Refer to «Air Cleaner Outlet Resonator Replacement»(ref-184141-S27322872682005082200000) .
2. Inspect the throttle body bore and throttle plate for deposits. You must open the throttle plate in order to inspect all of the surfaces.
3. Clean the throttle body bore and the throttle plate using a clean shop towel and top engine cleaner, GM P/N 1052626 (Canadian P/N 993026), or equivalent.
4. If the deposits are excessive, remove and disassemble the throttle body for cleaning. Refer to the following procedures: «Throttle Body Assembly Replacement»(ref-184141-S10374019962005082200000) «Throttle Position (TP) Sensor Replacement»(ref-184141-S24536292672005082200000) «Idle Air Control (IAC) Valve Replacement»(ref-184141-S03843010972005082200000)
5. After disassembly, clean the throttle body using a parts cleaning brush. DO NOT immerse the throttle body in any cleaning solvent.
6. If removed and disassembled for throttle body cleaning, assemble and install the throttle body. Refer to the following procedures: «Throttle Body Assembly Replacement»(ref-184141-S10374019962005082200000) «Throttle Position (TP) Sensor Replacement»(ref-184141-S24536292672005082200000) «Idle Air Control (IAC) Valve Replacement»(ref-184141-S03843010972005082200000)
7. Install the air cleaner outlet duct. Refer to «Air Cleaner Outlet Resonator Replacement»(ref-184141-S27322872682005082200000) .

Fuel Pressure Relief Procedure

Tools Required

J 34730-1A Fuel Pressure Gage. See Special Tools and Equipment .

1. Disconnect the negative battery cable. Refer to «Battery Negative Cable Disconnect/Connect Procedure (Single Battery)»(ref-184144-S12006988322005082200000) or «Battery Negative Cable Disconnect/Connect Procedure (Auxiliary Battery)»(ref-184144-S01033869922005082200000) in Engine Electrical.
2. Install the J 34730-1A . Refer to «Fuel Pressure Gage Installation and Removal»(ref-184136-S27071105092005082200000) .
3. Loosen the fuel fill cap in order to relieve fuel tank vapor pressure.
4. Open the valve on J 34730-1A in order to bleed the system pressure. The fuel connections are now safe for servicing.
5. Drain any fuel remaining in the gage into an approved container.
6. Once the system is completely relieved, remove the J 34730-1A .

Tools Required

J 34730-1A Fuel Pressure Gage. See Special Tools and Equipment .

J 41769 Fuel Line Quick Disconnect Tool. See Special Tools and Equipment .

J 44402 Fuel Tank Sending Unit Wrench. See Special Tools and Equipment .

Fuel System Cleaning

1. Remove the sending unit. Refer to «Fuel Sender Assembly Replacement»(ref-184141-S37316022562005082200000) .
2. Inspect the fuel strainer. Replace a contaminated strainer and inspect the fuel pump.
3. Inspect the fuel pump inlet for dirt and debris. Replace the fuel pump if you find dirt or debris in the fuel pump inlet.
4. Flush the fuel tank with hot water.
5. Pour the water out of the fuel sender assembly opening.
6. Rock the tank to be sure that removal of the water from the tank is complete.
7. Install the sending unit. Refer to «Fuel Sender Assembly Replacement»(ref-184141-S37316022562005082200000) .

Fuel Injector Cleaning Procedure

Tools Required

1. J 44466-12 CSFI Fuel Metering Body Jumper Block. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
2. J 44466-13 Screws. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
3. J 44466-11 IAFM Fuel Transfer Tube Recycling Block. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
4. J 41413 EVAP Pressure and Purge Station. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
5. J 44466-10 Regulator and Hose Assembly. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
6. J 39021 Fuel Injector Coil and Balance Tester. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
7. J 39021-210 Injector Tester Adapter Box. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
8. J 39021-301 V6 Fuel Injector Test Adapter. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .
9. J 38500-A Fuel Injector Cleaner. See «Special Tools and Equipment»(ref-184141-S19196316852005082200000) .

1. Loosen the fuel fill cap to relieve vapor pressure in the fuel tank.
2. Remove the positive crankcase ventilation (PCV) clean air tube from air inlet duct and set aside.
3. Remove the resonator and air inlet duct from throttle body.
4. Remove the brake booster vacuum hose and connector from intake manifold.
5. Remove the electrical connector from the central sequential fuel injection (CSFI) fuel metering body.
6. Remove the spark plug wires from 1, 3 and 5 from the distributor cap.
7. Remove the fuel line bolt (4) at the rear of intake manifold.
8. Relieve the fuel system pressure.
9. Remove the nuts (1) and clamp (2) from the fuel pipe.
10. Remove fuel pipes from the metering body.
11. Install the J 44466-12 (2) and the J 44466-13 (1) to the metering body and tighten.
12. Install the J 44466-11 (4), clamp (2) and J 44466-13 (1) to the fuel pipe and tighten.
13. Obtain the J 41413 , close the valve (2) on the tank (3), and remove the regulator assembly.
14. Install the J 44466-10 (5) to the J 41413 tank (3)
15. Connect the J 44466-10 hose (1) to the J 44466-12 (3).
16. Install the J 39021 , the J 39021-210 and J 39021-301 (4) to the metering body electrical connector.
17. Adjust the amperage selector switch on J 39021 to 0.5 amps.
18. Open the valve (2) on the tank (3).
19. Open the valve (4) on the J 44466-10 to pressurize the fuel system. Then close valve (4) before firing injectors. IMPORTANT: The minimum pressure required on the gage (6) is 150 psi. If 150 psi is not obtained, the tank (3) must be refilled prior to performing this procedure.
20. Fire one injector using the J 39021 . Observe a pressure drop on the gage (6) and verify the injector/poppet valve operation. An injector/poppet that is stuck and not operational will have no pressure drop on the gage. If an injector remains stuck, repeat the procedure multiple times (as required) until the injector is operational.
21. Repeat steps 19 and 20 for each individual injector to verify that all injector/poppet valve assemblies are unstuck and functional.
22. Shut off the pressure valve (2) on the tank (3) of the J 41413 .
23. Bleed off the pressure at the J 44466-10 .
24. Install the PCV fresh air tube to the air inlet duct.
25. Disconnect and remove the J 44466-10 (1) from the J 44466-12 (3) and the J 41413 .
26. Remove the J 39021-301 , J 39021-210 and J 39021 from the metering body.
27. Install the vehicle electrical connector to the metering body.
28. Install brake booster vacuum hose and connector to the intake manifold.
29. Install ignition wires 1, 3, and 5 to the distributor cap.
30. Install the resonator and air intake duct to the throttle body and hand tighten wing nut.
31. Obtain J 38500-A (2). IMPORTANT: Make sure the valve at the bottom of the canister (3) is closed.
32. Remove the canister top and add top engine cleaner GM P/N 1050002 (Canadian P/N 992872) to the canister.
33. Fill the remainder of the canister with regular unleaded gasoline and install the canister top.
34. Suspend J 38500-A from a convenient underhood location.
35. Connect the hose from J 38500-A (1) to the service port on the J 44466-12 (3).
36. Open valve (3) at the bottom of J 38500-A .
37. Connect a shop air source to the fitting at the top of J 38500-A and adjust the regulator (1) to 75 psi.
38. Let the vehicle run at idle until the canister is empty and the vehicle stalls.
39. Remove the shop air supply from J 38500-A .
40. Depressurize the J 38500-A .
41. Disconnect the J 38500-A hose from the J 44466-12 .
42. Remove the PCV clean air tube from the air inlet duct and set aside.
43. Remove the resonator and air inlet duct from the throttle body and set aside.
44. Remove ignition wires 1, 3, and 5 from the distributor cap.
45. Remove brake booster vacuum hose and connector from the intake manifold.
46. Bleed the residual pressure from J 44466-12 .
47. Remove J 44466-13 (1) and J 44466-12 (2) from the metering body.
48. Remove J 44466-13 (1), clamp (2) and J 44466-11 (4) from the fuel pipe (3).
49. Install the fuel pipe (3) to the metering body.
50. Install the clamp (2) and nuts (1). Tighten: Tighten the nuts to 3 N.m (27 lb ft).
51. Apply threadlock GM P/N 12345382 (Canadian P/N 10953489), or equivalent to the threads of the fuel pipe bolt (4).
52. Install the fuel pipe bolt. Tighten: Tighten the bolt to 6 N.m (53 lb ft).
53. Install the brake booster vacuum hose and connector to the intake manifold.
54. Install the resonator and air inlet duct to the throttle body.
55. Install the PCV clean air tube to the inlet duct.
56. Install brake booster vacuum hose and connector to the intake manifold.
57. Install ignition wires 1, 3, and 5 to the distributor cap.
58. Add 1 ounce of port fuel injector cleaner GM P/N 12345104 (Canadian P/N 12345515), or equivalent to the vehicle fuel tank for each gallon of gasoline estimated to be in the tank. IMPORTANT: Instruct the customer to add the remainder of the bottle of port fuel injector cleaner to the vehicle fuel tank at the next fill up.
59. Hand tighten the fuel tank filler cap.
60. Start the vehicle and check for fuel leaks.
61. Using a Tech II scan tool, check for any stored Powertrain DTC codes. Clear codes as required.
62. Disconnect Tech II scan tool. IMPORTANT: Advise the customer to change brands of fuel.

Powertrain

The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and fuel economy. The powertrain control module (PCM) is the control center of this system. The PCM monitors numerous engine and vehicle functions. The PCM constantly looks at the information from various sensors and other inputs, and controls the systems that affect vehicle performance and emissions. The PCM also performs the diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. Review the components and wiring diagrams in order to determine which systems are controlled by the PCM.

The following are some of the functions that the PCM controls

1. The engine fueling
2. The ignition control (IC)
3. The knock sensor (KS) system
4. The evaporative emissions (EVAP) system
5. The secondary air injection (AIR) system (if equipped)
6. The exhaust gas recirculation (EGR) system
7. The automatic transmission functions
8. The generator
9. The A/C clutch control
10. The cooling fan control

Powertrain Control Module Function

The powertrain control module (PCM) constantly looks at the information from various sensors and other inputs and controls systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the driver via the malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a buffered voltage to various sensors and switches. The input and output devices in the PCM include analog-to-digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that complete a ground or voltage circuit when turned on. Most PCM controlled components are operated via output drivers. The PCM monitors these driver circuits for proper operation and, in most cases, can set a DTC corresponding to the controlled device if a problem is detected.

Trip

A trip is an interval of time during which the diagnostic test runs. A trip may consist of only a key cycle to power up the powertrain control module (PCM), allow the diagnostic to run, then cycle the key off to power down the PCM. A trip may also involve a PCM power up, meeting specific conditions to run the diagnostic test, then powering down the PCM. The definition of a trip depends upon the diagnostic. Some diagnostic tests run only once per trip (i.e., catalyst monitor) while other tests run continuously during each trip (i.e., misfire).

Warm-Up Cycle

The powertrain control module (PCM) uses warm-up cycles to run some diagnostics and to clear any diagnostic trouble codes (DTCs). A warm-up cycle occurs when the engine coolant temperature increases 22° C (40° F) from the start-up temperature. The engine coolant must also achieve a minimum temperature of 71° C (160° F). The PCM counts the number of warm-up cycles in order to clear the malfunction indicator lamp (MIL). The PCM will clear the DTCs when 40 consecutive warm-up cycles occur without a malfunction.

Fuel Tank

The fuel tank stores the fuel supply. The fuel tank is located in the rear of the vehicle. The fuel tank is held in place by 2 metal straps that attach to the frame. The fuel tank is molded from high-density polyethylene.

Fuel Fill Pipe

The fuel fill pipe has a built-in restrictor in order to prevent refueling with leaded fuel.

Scheme 446

Note. If a fuel tank filler cap requires replacement, use only a fuel tank filler cap with the same features. Failure to use the correct fuel tank filler cap can result in a serious malfunction of the fuel and EVAP system.

The fuel fill pipe has a tethered fuel filler cap. A torque-limiting device prevents the cap from being over-tightened. To install the cap, turn the cap clockwise until you hear audible clicks. This indicates that the cap is correctly torqued and fully seated. A fuel filler cap that is not fully seated may cause a malfunction in the emission system.

Scheme 447

The fuel sender assembly consists of the following major components

1. The fuel level sensor (6)
2. The fuel tank pressure (FTP) sensor (1)
3. The fuel pump module (2)
4. The fuel strainer (3)

Scheme 448

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor card. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor which changes resistance in correspondence with the position of the float arm. The control module sends the fuel level information via the Class 2 circuit to the instrument panel cluster (IPC). This information is used for the IPC fuel gage and the low fuel warning indicator, if applicable. The control module also monitors the fuel level input for various diagnostics.

Fuel Pump

The fuel pump is mounted in the fuel sender assembly reservoir. The fuel pump is an electric high-pressure pump. Fuel is pumped to the fuel injection system at a specified flow and pressure. Excess fuel from the fuel injection system returns to the fuel tank through the fuel return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The control module controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

Fuel Strainer

The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel strainer normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or contamination.

Scheme 449

The fuel filter is located on the fuel feed pipe, between the fuel pump and the fuel injectors. The paper filter element (2) traps particles in the fuel that may damage the fuel injection system. The filter housing (1) is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature.

Fuel Feed and Return Pipes

The fuel feed pipe carries fuel from the fuel tank to the fuel injection system. The fuel return pipe carries fuel from the fuel injection system back to the fuel tank. The fuel pipes consist of 2 sections

1. The rear fuel pipe assemblies are located from the top of the fuel tank to the chassis fuel pipes. The rear fuel pipes are constructed of nylon.
2. The chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the fuel injection system. The chassis fuel pipes are constructed of steel.

Nylon Fuel Pipes

Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are 3 sizes of nylon pipes used

1. 9.53 mm (3/8 in) ID for the fuel feed
2. 7.94 mm (5/16 in) ID for the fuel return
3. 12.7 mm (1/2 in) ID for the vent

Heat resistant rubber hose or corrugated plastic conduit protect the sections of the pipes that are exposed to chafing, high temperature, or vibration.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if nylon fuel pipes are forced into sharp bends, the pipes kink and restrict the fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working on a vehicle with nylon fuel pipes.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female connector, provide the fuel seal. Integral locking tabs inside the female connector hold the fittings together.

Fuel Pipe O-Rings

O-rings seal the threaded connections in the fuel system. The fuel system O-ring seals are made of special material. Service the O-ring seals with the correct service part.

Scheme 450

The fuel meter body assembly (1) attaches to the lower intake manifold. The fuel meter body assembly performs the following functions

1. Distributes fuel evenly to the injectors (3)
2. Integrates the fuel pressure regulator (6) into the fuel metering system

Fuel Injectors

The Multec 2 fuel injector assembly is a solenoid device controlled by the control module that meters pressurized fuel to a single engine cylinder. The control module energizes the high-impedance, 12 ohms, injector solenoid to open a normally closed ball valve. This allows fuel to flow into the top of the injector, past the ball valve, and through a director plate at the injector outlet. The director plate has four machined holes that control the fuel flow, generating a spray of finely atomized fuel at the injector tip. Fuel from the injector tip is directed at the intake valve, causing the fuel to become further atomized and vaporized before entering the combustion chamber. This fine atomization improves fuel economy and emissions.

Scheme 451

The fuel pressure regulator is a diaphragm relief valve. The diaphragm has fuel pressure on one side and regulator spring pressure and intake manifold vacuum on the other side. The fuel pressure regulator maintains a constant pressure differential across the fuel injectors under all operating conditions. The fuel pressure regulator compensates for engine load by increasing fuel pressure as the engine vacuum drops.

Starting Mode

When the ignition is first turned ON, the control module energizes the fuel pump relay for 2 seconds. This allows the fuel pump to build pressure in the fuel system. The control module calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT), mass air flow (MAF), manifold absolute pressure (MAP), and throttle position (TP) sensors. The system stays in starting mode until the engine speed reaches a predetermined RPM.

Clear Flood Mode

If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the engine. When the TP sensor is at wide open throttle (WOT), the control module reduces the fuel injector pulse width in order to increase the air to fuel ratio. The control module holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the control module returns to the starting mode.

Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The control module ignores the signal from the heated oxygen sensor (HO2S). The control module calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions

1. The HO2S has varying voltage output, showing that the HO2S is hot enough to operate properly.
2. The ECT sensor is above a specified temperature.
3. A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the control module calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode

When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly. To prevent possible hesitation, the control module increases the pulse width to the injectors to provide extra fuel during acceleration. This is also known as power enrichment. The control module determines the amount of fuel required based upon the TP, the ECT, the MAP, the MAF, and the engine speed.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The control module monitors the corresponding changes in the TP, the MAP, and the MAF. The control module shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters.

Battery Voltage Correction Mode

When the battery voltage is low, the control module compensates for the weak spark delivered by the ignition system in the following ways

1. Increasing the amount of fuel delivered
2. Increasing the idle RPM
3. Increasing the ignition dwell time

Fuel Cutoff Mode

The control module cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability

1. The ignition is OFF. This prevents engine run-on.
2. The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
3. The engine speed is too high, above red line.
4. The vehicle speed is too high, above rated tire speed.
5. During an extended, high speed, closed throttle coast down-This reduces emissions and increases engine braking.
6. During extended deceleration, in order to prevent damage to the catalytic converters

Fuel Trim

The control module controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The control module monitors the HO2S signal voltage while in Closed Loop and regulates the fuel delivery by adjusting the pulse width of the injectors based on this signal. The ideal fuel trim values are around 0 percent for both short and long term fuel trim. A positive fuel trim value indicates the control module is adding fuel in order to compensate for a lean condition by increasing the pulse width. A negative fuel trim value indicates that the control module is reducing the amount of fuel in order to compensate for a rich condition by decreasing the pulse width. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the HO2S signal voltage. These changes fine tune the engine fueling. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. A scan tool can be used to monitor the short and long term fuel trim values. The long term fuel trim diagnostic is based on an average of several of the long term speed load learn cells. The control module selects the cells based on the engine speed and engine load. If the control module detects an excessively lean or rich condition, the control module will set a fuel trim diagnostic trouble code (DTC).

Check Gas Cap Message

The powertrain control module (PCM) sends a class 2 message to the driver information center (DIC) illuminating the Check Gas Cap message when any of the following occur

1. A malfunction in the evaporative emission (EVAP) system and a large leak test fails
2. A malfunction in the EVAP system and a small leak test fails

EVAP System Components

The evaporative emission (EVAP) system consists of the following components

EVAP Canister

The canister is filled with carbon pellets used to absorb and store fuel vapors. Fuel vapor is stored in the canister until the control module determines that the vapor can be consumed in the normal combustion process.

EVAP Purge Solenoid Valve

The EVAP purge solenoid valve controls the flow of vapors from the EVAP system to the intake manifold. The purge solenoid valve opens when commanded ON by the control module. This normally closed valve is pulse width modulated (PWM) by the control module to precisely control the flow of fuel vapor to the engine. The valve will also be opened during some portions of the EVAP testing, allowing engine vacuum to enter the EVAP system.

EVAP Vent Solenoid Valve

The EVAP vent solenoid valve controls fresh airflow into the EVAP canister. The valve is normally open. The control module commands the valve ON, closing the valve during some EVAP tests, allowing the system to be tested for leaks.

Fuel Tank Pressure Sensor

The fuel tank pressure (FTP) sensor measures the difference between the pressure or vacuum in the fuel tank and outside air pressure. The control module provides a 5-volt reference and a ground to the FTP sensor. The FTP sensor provides a signal voltage back to the control module that can vary between 0.1-4.9 volts. A high FTP sensor voltage indicates a low fuel tank pressure or vacuum. A low FTP sensor voltage indicates a high fuel tank pressure.

EVAP Service Port

The EVAP service port is located in the EVAP purge pipe between the EVAP purge solenoid valve and the EVAP canister. The service port is identified by a green colored cap.

Crankshaft Position (CKP) Sensor

The CKP sensor is a three wire sensor based on the magneto resistive principle. A magneto resistive sensor uses two magnetic pickups between a permanent magnet. As an element such as a reluctor wheel passes the magnets the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The PCM supplies a 12-volt, low reference, and signal circuit to the CKP sensor. The sensor returns a digital ON/OFF pulse 3 times per crankshaft revolution for the V6 engine, 4 times for the V8 engine. The CKP sensor reads the crankshaft mounted reluctor wheel to identify pairs of cylinders at top dead center (TDC).

Camshaft Position (CMP) Sensor

The CMP sensor is a hall-effect sensor located in the ignition distributor base, and uses the same type of circuits as the CKP sensor. The CMP sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The CMP sensor information is used by the PCM to determine the position of the valve train relative to the CKP.

Ignition Coil and ICM

The ICM is connected to the PCM by an ignition control (IC) circuit. The ICM also has a ground circuit and shares an ignition 1 voltage supply with the ignition coil. The coil driver in the ICM controls current through the ignition coil based on signal pulses from the PCM. There is no back-up or by-pass function in the ICM.

Secondary Ignition Components

The distributor is only used as a means to operate the CMP sensor and to distribute spark in the correct sequence. Since the distributor has no influence on base timing the distributor is not adjustable on V6 engines. The distributor position can be adjusted on V8 engines because the chance of crossfire between terminals is greater due to the proximity of the terminals. The spark is distributed through conventional carbon core wires to the spark plugs. The plugs are tipped with platinum for long wear and higher efficiency.

Powertrain Control Module (PCM)

The PCM controls all ignition system functions, and constantly corrects the basic spark timing. The PCM monitors information from various sensor inputs that include the following

1. The throttle position (TP) sensor
2. The engine coolant temperature (ECT) sensor
3. The mass airflow (MAF) sensor
4. The intake air temperature (IAT) sensor
5. The vehicle speed sensor (VSS)
6. The transmission gear position or range information sensors
7. The engine knock sensors (KS)

Purpose

The knock sensor (KS) system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The control module uses the KS system to test for abnormal engine noise that may indicate detonation, also known as spark knock.