EVAP System Operation

2000-02 Chevrolet Prizm
2003 Pontiac Vibe

For over three decades, vehicles have been equipped with EVAP systems. The purpose of the EVAP system has always been to collect evaporated gasoline (for instance during fill-up, while parked, and continuously while driving) and to burn the vapors during normal engine operation. This is a major factor in the reduction of unburned hydrocarbon emissions.

From the beginning, two things have remained constant. The vapors are collected in a canister containing activated charcoal granules. And manifold vacuum is used to draw the vapors into the engine. Everything else about the system has been refined, modified and improved to more effectively collect vapors, and to more precisely control when the vapors are drawn off and burned. And the specific details of operation also vary from one vehicle platform to another.

Today, the EVAP system is controlled by the PCM. And to meet OBD II requirements, the latest systems are largely self-diagnostic, and able to detect leaks as small as 0.020 inch (0.51 mm).

The EVAP system on the 2000-02 Chevrolet Prizm and the 2003 Pontiac Vibe (fig. 1) performs the same tasks and meets the same requirements as all other GM EVAP systems, but the control principles are somewhat different. This is explained in detail in the appropriate section of SI. As with all parts of SI, these sections are revised on a continuing basis. And an upcoming Service Manual update bulletin will itemize the latest revisions to SI.

Components
The Prizm/Vibe EVAP system consists of a vapor canister and three PCM-controlled solenoid valves. (This is one solenoid more than most EVAP systems use.) A fuel tank pressure sensor is used for diagnostics.

The vapor canister contains granules of carbon, which absorb gasoline vapors on contact. When air is drawn through the granules, the carbon gives up the vapors.

TIP: The canister in this system is unique in that it consists of two halves, or chambers. The chamber connected to the fuel tank is the vapor side of the canister, and the chamber connected to the air cleaner is the air supply side.

The Purge Solenoid valve is normally closed (no flow), and opens (flow) upon command from the PCM (fig. 2). This valve controls the application of manifold vacuum to purge the EVAP system.

The Vent Solenoid valve is normally open (flow), and closes (no flow) upon command from the PCM (fig. 3). This valve allows air from the air cleaner to enter the EVAP system.

The Pressure Switching Solenoid valve, located between the two chambers of the canister, is normally closed (no flow) (fig. 4). When necessary, it is opened (flow) by the PCM. When the valve is open, the vapor space in the fuel tank is connected to the canister.

Two additional valves are attached to the canister. They are operated by spring-loaded check balls and control flow into and out of the canister. The Evap Valve is on the vapor chamber side of the canister and the Atmospheric Valve is on the air chamber side.

The Fuel Tank Pressure Sensor is located on the top of the fuel tank (Vibe) or on the vapor canister (Prizm) (fig. 5).

EVAP System Components (fig. 6)

A  Canister
B  Vapor Chamber
C  Air Chamber
D  Fuel Tank
E  Purge Solenoid
F  Manifold Vacuum
G  Vent Solenoid
H  Pressure Switching Solenoid
J  Air Cleaner
K  Fuel Tank Pressure Sensor
L  EVAP Service Port
M  Evap Valve
N  Atmospheric Valve
P  Fuel Tank Vent Valve

Vapor Canister Fitting Identification (fig. 7)

A  From Vent Solenoid
B  From Fuel Tank
C  From Purge Solenoid
D  To Switching Solenoid (2)
E  From Fuel Tank (for refueling)
F  To Drain Hose

Operation
During shutdown, the valves assume their normal, relaxed positions.

Parked Shutdown (Cooldown) -- Both the purge valve and switching valve are closed and the vent valve is open. Under this condition, as vapors form in the fuel tank, they are routed to the canister. The calibration of the drain port passage check ball in the atmospheric valve is set at 5.5 in. H2O, and above that pressure, air is allowed to pass through the drain hose to atmosphere. On most other systems, this air is allowed to pass through the vent solenoid to atmosphere.

Normal Operation After Ambient Air (Cold) Start -- When engine coolant temperature reaches 74° C (165° F), the purge valve opens, applying manifold vacuum to the vapor chamber of the canister. Because the vent valve is already open, manifold vacuum draws air through the canister. This draws vapor into the engine to be burned. The switching valve remains closed.

As the fuel in the tank is heated by the nearby exhaust system, fuel evaporates and pressure within the tank increases.

TIP: This is an important fact to understand. During normal operation of the system, when the purge valve is turned on, and evacuation occurs, the pressure in the fuel tank does not drop. In fact, it may even increase. This does not indicate a problem during diagnosis.

After the vehicle reaches normal operating temperature, and other conditions are met, the PCM runs a series of EVAP self-diagnostic tests. The purpose of these tests is to identify whether each of the solenoid valves operates as commanded, and also to determine if there are any leaks in the system. Refer to the accompanying illustration as you read about the self-test processes.

Valve Positions Indicated by X = Closed, O = Open (fig. 8)

1. Normal Operation, During Purge
2. Large Leak Test, Vacuum Increase
3. Large Leak Test, Vacuum Decay
4. Small Leak Test
5. Final Test, Vent Solenoid
6. Final Test, Pressure Switching Solenoid

1. Normal Operation, During Purge -- Before these tests start, the vent valve is open, the switching valve is closed, and the purge valve is open.

2. Large Leak Test, Vacuum Increase -- First, the vent valve closes and the switching valve opens. The purge valve remains open. This causes vacuum to increase in the entire system. Vacuum is detected by the pressure sensor in the fuel tank. If the vacuum does not increase, or increases beyond the specified limit, P0440, P0441, and P0446 codes will set.

TIP: Because more than one code will set, it’s recommended that you begin diagnosis with the code set in Freeze Frame Failure Record.

3. Large Leak Test, Vacuum Decay -- The purge valve is now closed, trapping vacuum in the EVAP system. Now, the pressure sensor watches to see if, or how much, the vacuum decreases. A rapid decrease in vacuum indicates a large leak. This will cause a code P0440 to set. This could indicate a leaky filler cap, a loose fitting, or other large leak.

4. Small Leak Test -- If the system passes the large leak test, the pressure sensor continues to monitor the trapped vacuum. A slight vacuum decrease indicates a small leak. The EVAP system must be able to identify a leak as small as 0.5 mm (0.020 inch). If a small leak is detected, a code P0442 will set.

5. Final Test, Vent Solenoid -- Next, the system starts to open the vent valve, admitting air into the system once again. Vacuum should drop rapidly, indicating that the vent solenoid is working.

6. Final Test, Pressure Switching Solenoid -- Finally, the switching valve is closed. The indicated drop in vacuum is now not as rapid, because the pressure sensor in the tank is isolated from the rest of the system. This indicates that the switching valve is working.

After the test is completed, the solenoid valves return to the normal purge mode.

Once the system passes this final test, the EVAP system is declared OK, and the necessary “PASSED” flag sets in the PCM.

If the system fails any step of the self-test, diagnostic codes will set. SI contains the necessary steps to locate the cause(s) of the code(s).

Diagnostic Tips
IMPORTANT: Perform the necessary diagnostic steps before replacing any components.

If you find it necessary to use the J-41413-200 EVAP Tester (the “smoke machine”), you will need to plug the canister drain hose. Use plug J-41413-301 for this purpose. If you do not, smoke will blow from the opening. The check ball in the atmospheric valve is calibrated for 5.5 in. H2O, while the EVAP tester pressurizes the system to about 7-13 in. H2O.

TIP: One known place to check for leaks using the “smoke machine” was covered in the October 2002 TechLink. This involves the corrugated plastic vapor line between the top of the fuel tank and the vapor canister (fig. 9). It is possible that the O-ring seals used in this line are not functioning properly, or that the vapor line is not fully connected.

Remember, when the system is purging, with the purge valve open, pressure in the fuel tank does not drop as it does in other systems, and actually may increase. This is normal.

The Tech 2 contains several Service Bay tests, to expedite the diagnostic process.

The EVAP Purge/Seal Function Test allows you to simulate the leak portion of the test.

TIP: This test applies only to the Pontiac Vibe.

The test is performed with the engine running. At first the Tech 2 controls all three solenoid valves to see if it is possible to apply vacuum to the entire system, then it seals the system to see if it will hold vacuum. This checks valve operation and also checks for leaks.

The Check Mode is most often used while driving the vehicle to duplicate the customer concern.

TIP: This test applies both to Prizm and Vibe.

TIP: It’s important to capture and save any DTC or Freeze Frame information on the Tech 2 before entering the Check Mode. All DTC and Freeze Frame information is cleared when Check Mode is entered.

Using Check Mode temporarily makes the EVAP system much more sensitive to problems, so diagnostics will run quicker. It also temporarily turns all B codes into A codes, so the MIL will illuminate right away if a condition occurs.

- Thanks to Harry Cleaver, Frank Clark and Jeff Strausser

figure 9

Service Administrative
Messages on SI

http://service.gm.com is fast becoming the one-stop-shopping place for Service Information.

The following are now available to you in SI:
- Service manuals
- 2003 Owners Manuals
- Bulletins
- Service Administrative Messages (US)
- Campaigns
- Preliminary Information
- Service VMEs (US)

Here’s a little more detail on the latest addition, Service Administrative Messages.

Whenever GM sends out a Service Administrative Message over GM ACCESS, it will also be put on SI. You will no longer have to wait for the message to be relayed to you through your dealership’s communication system. You will have direct access to it through SI.

There are several ways to access the Service Administrative Messages.

If you know the number -- simply use the SI Number Search feature. You must type VSS followed by the Service Administrative Message number.

If you have already “built” the vehicle -- select Service Manuals/Bulletins, then use the keyword search. This will present you with a list of all documents in SI that use the keyword, pertaining to the specified vehicle. The Service Administrative Messages will be at the bottom of the list.

You also have another option if you have already “built” the vehicle -- select Service Manuals/Bulletins, then select Bulletins by Category (fig. 10), then select Service Administrative Message (fig. 11). This will present you a list of all Service Administrative Messages pertaining to the specified vehicle.

Updates
The Service Administrative Messages will be updated following the standard SI update schedule:
- update weekly on Internet
- update bi-weekly on broadcast
- update on CD whenever issued.

- Thanks to Bob Savo, Lisa Scott and Mark Stesney

Water in AIR System

Some 1999 - 2001 Jimmy, Blazer, and Bravada vehicles with the L35 4.3 L engine may experience a repeat DTC P0410 with evidence of water in the AIR pump. If there is evidence of water in the AIR pump, the pump must be replaced.

If the pump has been previously replaced, verify that the inlet and exhaust hoses are connected correctly before performing any additional diagnosis. Figure 14 shows the correct hose connection. Repeat failures have occurred because of these hoses being switched.

TIP: The inlet port on the pump is marked IN. As the hoses lie unconnected, it is very possible to assume that the reverse hose connection is correct.

If the hoses are connected correctly or this is the first repair of this concern on the vehicle, the source of the water could be either from the exhaust or the inlet side of the pump. To determine if the water originated from the exhaust side, follow the SI diagnosis for P0410 (Document ID 554347).

TIP: When you are at the step for testing the vacuum solenoid for proper operation, be sure to command the pump off and verify that the vacuum goes to zero. If not, the cause may be a stuck-open vacuum solenoid. Replace as necessary.

If you do not find an issue with the exhaust side of the system, water may be getting into the AIR system through the inlet hose and/or the pump itself. To prevent this, cut the existing inlet hose near the bend and attach a 2 foot (.6 m) length of heater hose, using a coupling (fig. 15).

TIP: For 1999 and early 2000 vehicles you will need 5/8-inch (15.9 mm) heater hose and coupling. For late 2000 and early 2001 you will need a 3/4-inch (19 mm) heater hose and coupling.

Route the hose along the right side of the engine compartment, ending at the evaporator core housing. Cut the hose at a 45° angle, with the angle pointing downward. This is a dry area, and it prevents kinking of the inlet hose, which can cause a restriction.

The exhaust check valves are also a source of water entry into the AIR pump. This can be diagnosed by inspection of the water found in the AIR pump. If the water has a yellow tint and has an exhaust odor, replace both check valves. Replacement of the shut-off valve is also recommended, due to the caustic nature of the exhaust water, which can cause failure of the diaphragm.

To insure no water enters the pump at the pump itself, add silicone sealer to the grommet at the wire harness leading into the pump.

- Thanks to Marty Case and Frank Tornambe

Typical Power Accessory Port
or Cigarette Lighter Removal

Park Brake Spring Kits

Vibe A/C Lack of Cooling

Door Switch Module Service

1999-2001 Cadillac Catera Transmission Control Module (TCM) DTCs P0601 and P0602

When diagnosing DTCs P0601 or P0602 set in the TCM, do not attempt to program the TCM. The TCM is not programmable and new replacement TCMs do not require programming. After replacing a TCM, clear all DTCs, using the Clear Eng/Trans DTC Info function on the scan tool. After replacing the TCM, if a DTC P0602 sets in the engine control module (ECM), clear all DTCs using the Clear Eng/Trans DTC Info function on the scan tool. If the DTC resets, update the ECM programming with the latest calibration available. The service manual information database has been updated to address this concern in SI.

- Thanks to Michael G. Van Houten

Folding Mirror Will Not Lock in Outboard Position

To duplicate a Pontiac Vibe key, use key blank p/n 88972631 and one of the key cutters in the accompanying chart. These key cutters are available from GM Dealer Equipment at 1.800.468.6657

- Thanks to Jeff Strausser

REMINDER
New Vehicle Prep -- Corvette Magnetic Selective Ride Control

Magnetic Selective Ride Control (RPO F55) is available on 2003 Corvettes. When the ignition is turned off, the dampers offer very little damping. So, plastic stuffers are inserted in the dampers for shipping from the factory (Techlink, June 2002).

The stuffers must be removed during new vehicle prep. Failure to do so will result in customer dissatisfaction with the vehicle’s ride quality. Refer to bulletin 02-03-11-002 for complete details.

You can recognize the presence of Ride Control three ways:
- Ride Control button on console
- Corrugated dust boots on dampers
- Yellow tabs protruding from dust boots

To remove the stuffers, lift the vehicle to allow the wheels to hang free. Reach from below, behind the tire. Compress the dust boot and pull the yellow tab to remove the stuffer (fig. 19).

TIP: There is a stuffer on each damper, front and rear.

After removing the stuffer, be sure to pull the dust boot down to cover the upper end of the damper tube (fig. 20).

- Thanks to Brad Thacher

Search Tip for Locating Product Information (PI) Documents on SI

Since June 17, 2002, it has been possible for you to search for PI documents on SI. However, some people are experiencing difficulties.

Here are some tips.

After entering SI, you must click on the blue line that says click here to enter a Vehicle Identification Number (VIN).

Next, input the vehicle’s VIN in the space provided. Be sure to include all 17 characters. Then click on Submit.

Next, choose Service Manual/Bulletins.

When the next screen comes up, you will see a keyword search box. Do not type anything in this box. The keyword search is not available for PI documents. Instead, look at the list at the bottom of the screen. Locate the line that says Preliminary Information and click on it (fig. 21).

You will now see a list of all PI documents that pertain to the VIN you input. You can then select any document for viewing (fig. 22).

- Thanks to GM Technical Assistance

4T65E
Automatic Transmission
Pump

figure 23

figure 24

Bulletins - October, 2002

This review of service bulletins released through mid-October lists the bulletin number, superseded bulletin number (if applicable), subject and models.

00 – General Information

02-00-89-016; Policy Reminder on New and/or Remanufactured GM Service Replacement Parts During Warranty Period; 2003 and Prior GM Passenger Cars and LD Trucks, Hummer H2

01 – HVAC

02-01-39-005; HVAC System Inoperative for a Drive Cycle, Poor HVAC System Performance in High Ambient Temperatures (Update HVAC Control Module Software); 2002-03 Chevrolet TrailBlazer, EXT, GMC Envoy, XL, Oldsmobile Bravada

03 – Suspension

01-03-10-010A; replaces 01-03-10-010; Inspection of Tire and Wheel Size Prior to Diagnosis of Transmission Shifts, Poor Performance, Speedometer, Cruise Control Concerns; 2001-02 Chevrolet, GMC Sierra with Duramax Diesel Engine and Allison Transmission

02-03-09-002A; replaces 02-03-09-002; Intermittent Boom, Rumbling Noise and/or Disturbance Heard in Passenger Compartment While Driving at Highway Speeds (Replace Rear Coil Springs); 2002-03 Chevrolet TrailBlazer, GMC Envoy with Rear Coil Springs

04 – Driveline Axle

02-04-95-001; Revised Differential Overhaul (11.5 Inch Axle) Procedure; 2001-02 Chevrolet Silverado, GMC Sierra Pickup Models

05 – Brakes

02-05-22-004A; replaces 02-05-22-004; Trailer Brakes Applied when Headlights/Park Lamps are On, Brake Controller Illumination (Modify Brake Controller Wiring Harness); 2002-03 Cadillac Escalade, EXT, Chevrolet Avalanche, 2001-03 Chevrolet Silverado, Suburban, Tahoe, GMC Sierra, Yukon, XL, 2003 Hummer H2

02-05-26-001; Rear Parking Brake Shoe Retaining Spring Clip Service Kit for Drum-in-Hat (DIH) Equipped Vehicles; Specified 1998-2003 vehicles

06 – Engine/Propulsion System

01-06-04-018A; replaces 01-06-04-018; Intermittent Malfunction Indicator Lamp (MIL) and PCM DTC P1404 (Recalibrate PCM); 2001 Buick Century, Chevrolet Impala, Malibu, Monte Carlo, Venture, Oldsmobile Alero, Silhouette, Pontiac Aztek, Grand Am, Grand Prix, Montana with 3.1L or 3.4L Engine (VINs J, E -- RPOs LG8, LA1)

02-06-01-023A; replaces 02-06-01-023; Oil Leak at Oil Cooler to Engine Block Mating Surface (Replace O-rings, Apply Sealant); 2001-03 Trucks with 6.6L Duramax Diesel Engine (VIN 1 -- RPO LB7)

02-06-01-029; Needle Bearings Found in Oil Pan (Replace Rocker Arms); Specified vehicles 1998-2003 with 4.8L, 5.3L, 5.7L or 6.0L V8 Engine (VINs V, T, G, S, U -- RPOs LR4, LM7, LS1, LS6, LQ4, LQ9)

02-06-02-008; New Engine Coolant Fill Procedure; 2003 Chevrolet Express, GMC Savana with 4.8L, 5.3L or 6.0L Gen III V8 Engine (VINs V, T, U -- RPOs LR4, LM7, LQ4)

02-06-04-046; Service Engine Soon Light On Intermittently and DTC P1441 Stored (Reprogram the PCM); 2002 Chevrolet Cavalier, Pontiac Grand Am with 2.2L Engine (VIN 4 -- RPO LN2)

02-06-04-047; Revised Eelctronic Ignition (EI) System Diagnosis; 2002 Chevrolet TrailBlazer, GMC Envoy, Oldsmobile Bravada with 4.2L Engine (VIN S -- RPO LL8)

02-06-04-048; Revised DTC P0540; 2001-02 Chevrolet Silverado, GMC Sierra Pickup Models with 6.6L Engine (VIN 1 -- RPO LB7)

02-06-04-049; Revised DTC P0201 -- P0208; 2001-02 Chevrolet Silverado, GMC Sierra Pickup Models with 6.6L Engine (VIN 1 -- RPO LB7)

07 – Transmission/Transaxle

99-07-30-016A; replaces 99-07-30-016; Diagnostic Information for Intermittent Transmission Downshift, Slip, Busy/Cycling TCC or Noisy Cooling Fan; 2003 and Prior LD Trucks, Hummer H2 with Automatic Transmission

02-07-30-029A; replaces 02-07-30-029; New Powertrain Quality Cener for Engine and Transmission Assembly Replacement; 2003 and Prior Passenger Cars and LD Trucks, Hummer H3

02-07-30-032; Allison Transmission Control Module Fast Learn Procedure Update Required After Transmission Repairs; 2002-03 Chevrolet Silverado, GMC Sierra with Allison 1000 Series Automatic Transmission

08 – Body and Accessories

01-08-46-008A; replaces 01-08-46-008; Information on Upgrading Factory Installed ONStar Generation 2.0 Equipped Vehicles to Generation 2.6; Specified 2000-01 Vehicles with Factory Installed OnStar

02-08-49-007; Center Console Lid Hard to Open or Close (Lubricate Center Console Lid Latch); 1999-2003 Chevrolet Silverado, Suburban, Tahoe, GMC Sierra, Yukon, XL with Split Front Seats (RPO AE7)

02-08-49-008; Latch Replacement -- Instrument Panel (IP Compartment) Procedure; 2000-03 Chevrolet Malibu

02-08-64-020; Passenger Door Outside Rearview Mirror Vibration (Install New Reinforcement Bracket); Specified 1997-2001 MD Tilt Cab Models

09 – Restraints

02-09-40-003; Passenger Seat Shoulder Belt Too Tight or Cinches Up (Replace Passenger Seat Belt Retractor Assembly); 2002 Chevrolet TrailBlazer, EXT, GMC Envoy, XL, Oldsmobile Bravada

02-09-40-004; Front Seat Belt Buckles May Interfere with Door Panels (Relocate New Buttons on Webbing); 2000-02 Chevrolet Monte Carlo

02-09-41-002; Air Bag Lamp On, Passenger Air Bag Indicator Always Reads OFF, DTC B0092 Set (Repair Passenger Presence System PPS Sensor Harness); 2003 Cadillac Escalade, EXT, Chevrolet Avalanche, Silverado, Suburban, Tahoe, GMC Sierra, Yukon, XL with Sensor Indicator Inflatable Restraint Front Passenger/Child Presence Detector (RPO ALO)