V6/v8 Pfi Component Test Pontiac Fiero I

MODEL IDENTIFICATION

Note. The following conditions must be met before testing: Engine at operating temperature, Engine in closed loop operation, Engine idling ("Engine Run" column), Test terminal NOT grounded, and Scanner or ALDL tool NOT installed.

Repair procedures in this article are sometimes identified by a specific body code. The following table lists GM division, model name, and body types that apply to the body codes.

MODEL IDENTIFICATION

DESCRIPTION

The computerized engine control system monitors as many as 19 engine/vehicle functions. (Scheme 347) This system controls engine operation and lowers exhaust emissions while maintaining fuel economy and driveability. The Electronic Control Module (ECM) is the "brain" of the CCC system.

The computerized engine control system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When the ideal air/fuel ratio is maintained, the 3-way catalytic converter can control Oxides of Nitrogen (NOx), Hydrocarbon (HC) and Carbon Monoxide (CO) emissions.

ECM Conditions Sensed & Systems Controlled. Scheme 347

DIAGNOSTIC SYSTEM OPERATION

The ECM of computerized engine control system is equipped with a self-diagnostic system which detects system failures or abnormalities. As a bulb and system check, "SERVICE ENGINE SOON" light will glow when ignition switch is turned to "ON" position and engine is not running. When engine is started, light should go out. If not, a malfunction has been detected in the computerized engine control system or "SERVICE ENGINE SOON" light circuit is faulty.

When a malfunction occurs, ECM will illuminate the "SERVICE ENGINE SOON" light located on instrument panel. When malfunction is detected and light is turned on, a corresponding trouble code will be stored in ECM memory. Malfunctions are recorded as "hard failures" or as "intermittent failures".

"HARD FAILURES"

Hard failures cause "SERVICE ENGINE SOON" light to glow and remain on until the malfunction is repaired. If light comes on and remains on during vehicle operation, cause of malfunction must be determined using diagnostic charts. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is driveable, but loss of good driveability will most likely be encountered.

"INTERMITTENT FAILURES"

Intermittent failures cause "SERVICE ENGINE SOON" light to flicker or illuminate and go out about 10 seconds after the intermittent fault goes away. The corresponding trouble code, however, will be retained in ECM memory. If related fault does not reoccur within 50 engine restarts, related trouble code will be erased from ECM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in the CEC TESTS W/O CODES article in this section.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds. Others may require operation for 5 minutes or longer under engine load. For code testing procedures, refer to the V6 & V8 PFI TESTS/CODES article in this section.

BASIC DIAGNOSTIC PROCEDURE

Note. Most computerized engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoses. Before considering the computer system as a possible cause of problems, ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

Diagnosis of the computerized engine control system should be performed in the following order

1. Make sure that all engine systems not related to the computer system are operating properly. Do not proceed with testing unless all other problems have been repaired.
2. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If trouble codes were displayed (other than Code 12), decide whether codes are "hard" or "intermittent" trouble codes. "Hard" codes will cause the "SERVICE ENGINE SOON" light to illuminate continuously while engine is running. See ECM TROUBLE CODE DEFINITIONS table in the V6/V8 PFI TESTS/CODES article in this section.
3. If no trouble codes were displayed, perform FIELD SERVICE MODE CHECK procedures.
4. If no trouble is indicated by the FIELD SERVICE MODE check and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS and/or SCAN TESTER USAGE in the TROUBLE SHOOTING procedures in the CEC TESTS W/O CODES article in this section. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
5. After any repairs are made, clear any trouble codes and perform FIELD SERVICE MODE check again. For code clearing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

ALDL Connector Terminal Identification. Scheme 348

DIAGNOSTIC MATERIALS

Note. The charts described in the following paragraphs are arranged later in this article, by engine size and fuel system type.

DIAGNOSTIC CHARTS

The diagnostic charts are used to find and repair problems which the on-car diagnostics have found. These charts include

1. Charts which test the reliability of the self-diagnostic system.
2. Charts which help fix problems which are "SERVICE ENGINE SOON" light related.
3. Charts which test the computerized fuel control system performance.
4. Charts which help fix a problem when the on-car diagnostics don't work.
5. ENGINE CRANKS BUT WON'T RUN charts. Refer to the appropriate TROUBLE SHOOTING chart in the CEC TESTS W/O CODES article in this section.
6. Charts where a stored trouble code leads you to a particular problem. See ECM TROUBLE CODE DEFINITION and DIAGNOSTIC AIDS in the V6/V8 PFI TESTS/CODES article in this section. Charts which are used because the FIELD SERVICE MODE CHECK found a problem.

Note. Although there are many charts connected with computer diagnosis, only 2 charts are needed to prove system is operating properly. Normally, only 3 charts are necessary to find a problem, if one exists.

DIAGNOSTIC AIDS

Diagnostic aids (located in each "trouble code" chart box for each system) are additional tips used to help diagnose trouble codes when inspected circuit checks out okay. Diagnostic aids may help lead to a definitive solution to that trouble code problem. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

FIELD SERVICE MODE CHECK (FUEL INJECTED MODELS)

On fuel injected models, "SERVICE ENGINE SOON" light will indicate operational mode of engine if ALDL is grounded while engine is running. In closed loop mode, "SERVICE ENGINE SOON" light will flash at a rate of one flash per second. In open loop, light will flash at a rate of 2.5 flashes per second. If light is off all or most of the time, a lean exhaust is indicated. If light is on all or most of the time, a rich exhaust is indicated.

This test confirms proper operation of fuel system and verifies closed loop operation. Clear codes and perform this test after any repair is completed. When performing this check, always engage parking brake and block DRIVE wheels. Parking brake on front-wheel drive models does NOT hold drive wheels. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

Note. On some engines, oxygen sensor will cool off after only a short period of time while engine is idling. This will cause engine to go into open loop. To restore closed loop mode, run engine at part throttle several minutes and accelerate from idle to part throttle several times.

SPECIAL DIAGNOSTIC TOOLS

Note. Special "Scan" testers plugged into the ALDL may be used to read trouble codes and check voltages in the system on the serial data line (terminal "E" on EFI and terminal "M" on EFI with P-4 systems). These testers can save a great deal of time. For additional information see SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS table in this article. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

The computerized engine control system is most easily diagnosed using a "Scan" tester, however, other tools may aid in diagnosing problems if a "Scan" tester is unavailable. These tools are: a tachometer, a dwell meter, test light, ohmmeter, digital voltmeter with 10-megohm impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights (TBI and PFI) and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connector at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart.

Note. If engine operation seems to change when dwell meter is connected to Green wire, remove dwell meter and use another type. A few brands are not compatible with computerized engine control system.

When engine is at operating temperature and idling, dwell meter needle should vary between 10-50 degrees. This indicates closed loop operation. Before engine reaches operating temperature, dwell should be fixed between 10-50 degrees, indicating open loop operation. If after reaching normal operating temperature dwell is fixed between 10-50 degrees, less than 10 degrees or more than 50 degrees, refer to appropriate CHART A - DWELL FIXED diagnostic chart for that system.

SCAN TESTER USAGE

Note. Prior to connection of scan tester to vehicle, diagnostic system should be checked to determine if system is operating properly and if information received by scan tester will be accurate. This is done by performing appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If vehicle does not pass diagnostic circuit check, information received by scan tester may be invalid. CCC Scan tester is a specialized tester which, when plugged into ALDL, can be used to diagnose on- board computer control stems by providing instant access to circuit voltage information without need to crawl under dash or hood to back-probe sensors and connectors.

Scan testers cut down diagnostic time dramatically by furnishing input data (voltage signals) which can be compared to specification parameters. See SCAN TESTER - TEST DATA PARAMETERS table. They also furnish information on output device (solenoids and motors) status. Status parameters, however, are only an indication that output signals have been sent to devices by the ECM. It does not indicate if devices have responded properly to that signal. This will need to be verified at output device using a voltmeter or test light.

Note. Code 12 should always exist when ALDL is grounded with key on and engine not running but may not be indicated by all makes of scan tester.

If trouble codes are not present, this is not an indication that there is not a problem. CCC related problems are about 20 percent codes and 80 percent driveability. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Use of a scan tester is easiest method of checking sensor specifications and other data parameters. Tester is also useful in finding intermittent wiring problems by wiggling wiring harnesses and connections (key on, engine off) while observing data parameters. See the SCAN TESTER - TEST DATA PARAMETERS table below. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

Note. Information obtained by scan tester is only as accurate as the tester itself. If erroneous voltage signals are suspected, it will be necessary to verify tester information using a digital voltmeter and wiring schematic. If non- existent codes are evidenced, turn ignition off, remove tester, turn ignition on. Ground ALDL "DIAGNOSTIC TERMINAL". If same codes are not flashed by "SERVICE ENGINE SOON" light that were indicated by scan tester, tester cannot be used on vehicle as information obtained by it may not be accurate.

SCAN TESTER - TEST DATA PARAMETERS

Note. Information in the following tables is typical readings taken on vehicle with engine idling, upper radiator hose hot, closed throttle, transmission in Park or Neutral, "closed loop" status achieved and all accessories off (except as noted in tables). Data parameters are updated every 1 1/4 seconds. On systems using P-4 computers, parameter updates are virtually instantaneous. Not all devices & systems are used on all models.

PORT FUEL INJECTION

Note. This ECM voltage chart can be used with a digital voltmeter to help save time in diagnosis. Voltages on the car being tested my vary slightly from these due to battery or alternator charging level.

DIAGNOSTIC CIRCUIT CHECK (ALL ENGINES)

The diagnostic circuit check is an organized approach for identifying a problem caused by the fuel injection system. Driver comments normally fall into one of the following areas: steady "SERVICE ENGINE SOON" light, driveability problem and engine "CRANKS BUT WON'T RUN".

DIAGNOSTIC CIRCUIT CHECK PROCEDURES

1. Steady "SERVICE ENGINE SOON" light with the ignition on and engine not running confirms battery voltage to the ECM.
2. Code 12 should flash 3 times, followed by any other trouble codes stored in memory. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.
3. Record all stored trouble codes (except Code 12).
4. With the engine running and the diagnostic terminal grounded, the ECM will respond to the oxygen sensor signal voltage and use the "SERVICE ENGINE SOON" light to display this information as follows: Closed loop confirms the O2 sensor signal is being used by the ECM to control fuel delivery, and the system is working normally. Signal voltage will vary from below .35 to above .55 volts. Open loop indicates that oxygen sensor voltage is unusable to the ECM. Signal voltage is a constant value between .35 and .55 volts. System will flash open loop from 30 seconds to 2 minutes after engine starts or until sensor reaches normal operating temperature. If system fails to go to closed loop, see Code 13. "SERVICE ENGINE SOON" light out indicates lean exhaust. Oxygen sensor signal voltage will be less than .35 volts and steady. "SERVICE ENGINE SOON" light on steady indicates rich exhaust. O2 sensor signal voltage will be greater than .55 volts and steady.
5. Road test of the vehicle using field service mode must be done at steady speeds. In this mode, the following conditions may be observed and are considered normal: light on too long under acceleration, light off too long under deceleration, light on too long with idle below 1200 RPM.
6. Clearing codes. Ignition should be off. Remove continuous battery fuse for 30 seconds. Fuse and holder are located near battery.

"SCAN" DIAGNOSTIC CIRCUIT CHECK

The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an assembly line communication link (ALCL). This communication link can provide diagnostic information for display on any "SCAN" tester designed for this purpose.

1. If the "SCAN" tester is not operating, check tester on another vehicle. If okay, the cigar lighter socket should be checked for 12-volts and a good ground. With the ignition on, if the "SCAN" tester reads "no data" or "no ALCL", check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line should vary between 2-5 volts and the diagnostic line should have about 5 volts. See SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS in this article.

Flow Chart, Diagnostic Circuit Check. Scheme 349

Flow Chart, Diagnostic Circuit Check. Scheme 350

CHART A1 - NO "SERVICE ENGINE SOON" LIGHT (2.8L)

"SERVICE ENGINE SOON" light should be on steady when ignition is on and engine is not running. Battery voltage is supplied directly to the bulb. The ECM turns the light on by grounding circuit No. 419 at the ECM.

If both continuous battery supply voltages are lost at terminals No. "B1" and "C16" or the ignition feed to terminal No. "A6" is not present, the "SERVICE ENGINE SOON" light will not come on.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If the "SERVICE ENGINE SOON" fuse is blown, locate and correct short to ground in Code 54 circuit.
2. Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is present.

Engine Runs Okay, Check The Following

1. Faulty light bulb.
2. Circuit No. 419 has an open.
3. Fuel gauge fuse is blown. This will result in no stop, oil or alternator warning lights.

Engine Cranks But Will Not Run, Check The Following

1. Continuous battery power, fuse or fusible link is open.
2. ECM fuse has a open.
3. Battery circuit No. 340 to ECM is open.
4. Ignition circuit No. 439 to ECM is open.
5. Poor plug connection at ECM.

Flow Chart A1, No "Service Engine Soon" Light (2.8L). Scheme 351

Flow Chart A1, No "Service Engine Soon" Light (2.8L). Scheme 352

CHART A1 - NO "SES" LIGHT (5.0/5.7L)

There should always be a steady "SERVICE ENGINE SOON" ("SES") light with ignition on and engine stopped. Battery is supplied directly to the light bulb. The ECM controls the light and turns it on by providing a ground path through circuit No. 419 to the ECM.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test will determine if the ECM has the ability to ground circuit No. 419.
2. If both the continuous battery supply voltages are lost at terminals "B1" and "C16" or the ignition feed to terminal "A6" is not present, the "SERVICE ENGINE SOON" light will not come on with the ignition on.

Engine Runs Okay

1. Check for a faulty light bulb.
2. Check for an open in circuit No. 419.

Engine Cranks But Will Not Run

1. Continuous battery drain, check fusible link for open.
2. Check battery circuit No. 340 to ECM for open.
3. Check ignition circuit No. 439 to ECM for open.
4. Check for poor connection at ECM.
5. Check for faulty ECM ground circuits.

Flow Chart A1, No "Service Engine Soon" Light (5.0/5.7L). Scheme 353

Flow Chart A1, No "Service Engine Soon" Light (5.0/5.7L). Scheme 354

(ALL ENGINES)

Steady "SERVICE ENGINE SOON" light should be on with ignition on and engine not running. Battery voltage is supplied directly to the bulb. With the diagnostic terminal grounded the light should flash a Code 12 followed by any other trouble codes stored in memory. A steady light indicates a short to ground in light control circuit No. 419, or an open in circuit No. 451. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If there is a problem with the ECM that causes a "SCAN" tester not to read "Serial Data", the ECM should not flash a Code 12. If Code 12 is flashing, check for a short in circuit No. 451. If Code 12 does flash be sure that "SCAN" tester is working properly on another vehicle. If "SCAN" tester is functioning properly and circuit No. 461 is okay, the Mem-Cal or ECM may be at fault for the "NO ALDL" symptom.
2. If the light goes off when the ECM connector is disconnected, circuit No. 419 is not shorted to ground.
3. This test will check for an open in diagnostic circuit No. 451.
4. At this point the wiring to the "SERVICE ENGINE SOON" light is okay. The problem could be a faulty ECM or Mem-Cal. If Code 12 does not flash, the ECM should be replaced using the original Mem-Cal. Replace the Mem-Cal only after trying a new ECM unit. Solenoids are turned on and off by the ECM, using internal electronic switches called "Drivers". Each driver is part of a group of 4, called "Quad-Drivers". Failure of one driver can damage any other driver in the set.

Flow Chart A2, Won't Flash Code 12 "SES" Light On Steady (All Eng). Scheme 355

Flow Chart A2, Won't Flash Code 12 "SES" Light On Steady (All Eng). Scheme 356

CHART A3 (1 of 2) - ENGINE CRANKS, BUT WON'T RUN (2.8L)

Battery condition and engine cranking speed are okay, and there is adequate fuel in the tank. If engine starts but immediately stalls, see INTERMITTENTS in the TROUBLE SHOOTING tests of the CEC TESTS W/O CODES article in this section.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This chart assumes that battery, condition and engine cranking speed are okay, and there is adequate fuel in the tank. If engine starts but immediately stalls, see TROUBLE SHOOTING in the CEC TESTS W/O CODES article in this section. A "SERVICE ENGINE SOON" light is a basic check for ignition and battery supply to the ECM.
2. No spark indicates a basic HEI problem.
3. This test will determine if the ECM is receiving the reference signal and controlling the injectors. This test could also be performed at the 4-way injector connector by using a test light between terminals "A" and "D".
4. Using Pressure Gauge (J 34730 1), wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge.

An EGR valve sticking open can cause a low air/fuel ratio during cranking. Unless engine enters "Clear Flood" at the first indication of a flooding condition, it can result in a no start condition.

Check for fouled plugs. If the TPS is sticking or binding in the wide open throttle position, the ECM will be in the "Clear Flood" mode. A defective cold start circuit or water in fuel line can cause a no start in cold weather. To check cold start circuit, see CHART A9.

A defective MAF sensor may cause a no start or stall after start. To determine if the sensor is causing the problem, disconnect it. The ECM will then use a default value for the sensor, and if the condition is corrected and the connections are okay, replace the sensor. Also check that injectors on both side of engine will cause a test light to blink.

If above checks are okay, see "Hard Starting" in the CEC TESTS W/O CODES article in this section.

Flow Chart A3, (1 of 2) Engine Cranks, But Won't Run (2.8L). Scheme 357

Flow Chart A3, (1 of 2) Engine Cranks, But Won't Run (2.8L). Scheme 358

CHART A3 (2 of 2) - ENGINE CRANKS, BUT WON'T RUN (2.8L)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 5) Checks for 12-volts to injectors.
2. 6) This test will determine if the distributor module is not generating the reference pulse or if the wiring or ECM are at fault. By touching circuit No. 430 with a test light a reference signal is being generated. If the test light blinks at the injector, then the ECM and wiring are okay.
3. 7) Each time the test light touches circuit No. 430, the ECM should turn on the fuel pump for 2 seconds.
4. 8) All checks made to this point would indicate that the ECM is at fault. However, there is a possibility of circuits No. 467 or 468 being shorted to a voltage source either in the engine harness or in the injector harness.

To test for this condition, disconnect the 4-way injector connector. Turn ignition on. Probe circuits No. 467 and 468 on the ECM side of harness with a test light connected to ground. There should be no light. If okay, check the resistance of the injector harness between terminals "A"-"C", "A"-"D", "B"-"D" and "B"-"C". Ohm resistance should be more than 4 ohms.

If less than 4 ohms check harness for wires shorted together and check resistance of each injector. Resistance should be more than 10 ohms. If all is okay, replace ECM.

Flow Chart A3, (2 of 2) Engine Cranks, But Won't Run (2.8L). Scheme 359

Flow Chart A3, (2 of 2) Engine Cranks, But Won't Run (2.8L). Scheme 360

CHART A3 (1 of 2) - ENGINE CRANKS, BUT WON'T RUN (5.0/5.7L)

This chart assumes that battery condition and engine cranking speed are okay, and there is adequate fuel in the tank.

Note. Test numbers refer to test numbers on diagnostic chart.

1. A "SERVICE ENGINE SOON" light, is a basic test to determine if there is 12 volts to the ECM. No ALDL may be due to an ECM problem and CHART A2 will diagnose the ECM. If TPS is over 2.5 volts, the engine may be in the "Clear Flood" mode, which will cause starting problems. The engine will not start without reference pulses and, therefore, the "SCAN" tester should read RPM (reference) while cranking.
2. No spark may be caused by one of several components related to the ignition system. CHART C4 will cover all problems related to the causes of a no spark condition.
3. The test light should blink, indicating the ECM is controlling the injectors okay. How bright the light blinks is not important.
4. Using Fuel Pressure Gauge (J 34730 1), wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge.

An EGR valve sticking open can cause a low air/fuel ratio during cranking. Unless engine enters "Clear Flood" at the first indication of a flooding condition, it can result in a no start.

Check for fouled plugs. A defective cold start circuit or water in fuel line can cause a no start condition in cold weather. See CHART A9. A defective MAF sensor may cause a no start or a stall after start. To determine if the sensor is causing the problem, disconnect it. The ECM will then use a default value for the sensor, and if the condition is corrected and the connections are okay, replace the sensor.

Also check that injectors on both sides of engine will cause a test light to blink. If not okay, check injector fuses. If above checks are all okay, see the CEC TESTS W/O CODES article in this section.

Flow Chart A3, (1 of 2) Engine Cranks/Won't Run (5.0/5.7L). Scheme 361

Flow Chart A3, (1 of 2) Engine Cranks/Won't Run (5.0/5.7L). Scheme 362

CHART A3 (2 of 2) - ENGINE CRANKS, BUT WON'T RUN (5.0/5.7L)

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for 12 volts to injectors. Due to the injectors wired in parallel there should be a light on at both terminals.
2. Checks continuity of circuits No. 467 and 468.
3. All checks made to this point would indicate that the ECM is at fault. However, there is a possibility of circuits No. 467 or 468 being shorted to a voltage source either in the engine harness or in the injector harness.

To test for this condition, disconnect all injectors. Turn ignition on. Probe circuits No. 467 and 468 on the ECM side of injector harness with a test light connected to ground (test one injector harness on each side of engine). There should no light. If light is on, repair short to voltage. If okay, check resistance of the injectors. Resistance should be 10 ohms or more.

Check injector harness connector. Be sure terminals are not backed out of connector and contacting each other. If all is okay, replace ECM.

Flow Chart A3, (2 of 2) Engine Cranks/Won't Run (5.0/5.7L). Scheme 363

Flow Chart A3, (2 of 2) Engine Cranks/Won't Run (5.0/5.7L). Scheme 364

CHART A7 (1 OF 2) - FUEL SYSTEM DIAGNOSIS (2.8L)

With the ignition on, the ECM will turn on the in-tank fuel pump. It will remain on as long as the engine is cranking or running, and the ECM is receiving HEI distributor reference pulses.

If there are no reference pulses, the ECM will shut off the fuel pump within 2 seconds after the ignition is turned off or engine is stopped. The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled between 34-46 psi (2.3-3.0 kg/cm 2 ). Excess fuel is then returned to the fuel tank.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Use Pressure Gauge (J 34730 1). Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge. With the ignition on fuel pressure should about 40-47 psi (2.8-3.2 kg/cm 2 ). This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on barometric pressure, however, the pressure idling was less indicating a defective pressure regulator control.
3. Pressure that continues to fall is caused by one of the following conditions: In-tank fuel pump check valve not holding. Pump coupling hose or pulsator leaking. Fuel pressure regulator valve leaking. Injector sticking open.
4. Check for an injector sticking open by checking for a fouled or saturated spark plug. If a leaking injector can not be determined by a fouled or saturated spark plug the following procedure should be used Remove plenum, cold start valve and fuel rail bolts. Reconnect cold start valve. Connect a hose to valve nozzle and insert into a gasoline container. Lift fuel rail out just enough to leave injector nozzles in the ports. Pressurize fuel system. Lift each side of rail up and check for injector leaking.
5. See appropriate TROUBLESHOOTING procedures in the CEC TESTS W/O CODES article in this section.

Flow Chart A7, (1 of 2) Fuel System Diagnosis (2.8L). Scheme 365

Flow Chart A7, (1 of 2) Fuel System Diagnosis (2.8L). Scheme 366

CHART A7 (2 OF 2) - FUEL SYSTEM DIAGNOSIS (2.8L)

Note. Test numbers refer to test numbers on diagnostic chart.

1. If fuel pressure is less than 40 psi (2.8 kg/cm 2 ) check the following: System has regulated pressure but pressure is less than 40 psi (2.8 kg/cm 2 ). The Amount of fuel to the injectors is okay, but fuel pressure is too low. Fuel system will be lean running and may set Code 44. Also, vehicle is hard starting cold and has overall poor performance. Restricted fuel flow that causes pressure drop. Normally a vehicle with a fuel pressure of less than 24 psi (1.6 kg/cm 2 ) at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop as pressure begins to drop rapidly.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the pump test terminal, pressure should be above 60 psi (4.1 kg/cm 2 ).
3. This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Flow Chart A7, (2 Of 2) Fuel System Diagnosis (2.8L). Scheme 367

Flow Chart A7, (2 Of 2) Fuel System Diagnosis (2.8L). Scheme 368

CHART A7 (1 OF 2) - FUEL SYSTEM DIAGNOSIS (5.0/5.7L)

The ECM turns the in-tank fuel pump on for 2 seconds when the ignition is turned on. It will turn it on again during cranking and will keep it on as long as the engine is running or cranking and the ECM is receiving HEI distributor reference pulses. If there are no reference pulses, the ECM will shut the fuel pump off within 2 seconds after the key is turned on or engine is stopped. The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to 34-47 psi (2.4-3.3 kg/cm 2 ) with the ignition on, engine stopped or during wide open throttle (WOT). Excess fuel is returned to the fuel tank.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Install Pressure Gauge (J-34730-1). Wrap a shop towel around fuel pressure tap to absorb any fuel spillage when installing gauge. With ignition on, pump pressure should be 41-47 psi (2.8-3.3 kg/cm 2 ). This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure is low (high vacuum). Manifold pressure is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure. The idle pressure will vary slightly depending on barometric pressure, however, the pressure idling is less indicating pressure regulator control.
3. Pressure that continues to fall is caused by one of the following: in-tank fuel pump check valve not holding, pump coupling hose leaking, pressure regulator valve leaking or an injector is sticking open.
4. An injector sticking open can best be determined by checking for a fouled or fuel saturated spark plug(s). If a leaking injector can not be located by a fouled or fuel saturated spark plug the following procedure should be used: Remove plenum, cold start valve and fuel rail bolts. Reconnect cold start valve. Connect a hose to valve nozzle and insert into a gasoline container. Lift fuel rail out just enough to leave injector nozzles in the ports. Pressurize the fuel system. Lift each side of rail up and observe for injectors leaking.
5. See TROUBLESHOOTING in the CEC TESTS W/O CODES article in this section.

Flow Chart A7, (1 Of 2) Fuel System Diagnosis (5.0/5.7L). Scheme 369

Flow Chart A7, (1 Of 2) Fuel System Diagnosis (5.0/5.7L). Scheme 370

CHART A7 (2 OF 2) - FUEL SYSTEM DIAGNOSIS (5.0/5.7L)

Note. Test numbers refer to test numbers on diagnostic chart.

1. If fuel system has pressure, but less than 41 psi (2.8 kg/cm 2 ), perform the following tests: Regulated pressure, but less than 41 psi (2.8 kg/cm 2 ). Amount of fuel to injectors is okay but pressure is too low. System will be lean running and may set Code 44. Can also be hard starting cold and poor overall performance. Restricted flow causing pressure drop. Normally, a vehicle with a fuel pressure of less than 24 psi (1.7 kg/cm 2 ) at idle will not be driveable. If the pressure drop occurs only while driving, the engine will surge and then stop as pressure drops rapidly.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure. When battery voltage is applied to the ALCL pump terminal "G", pressure should be approximately 60 psi (4.2 kg/cm 2 ).
3. This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

Flow Chart A7, (2 Of 2) Fuel System Diagnosis (5.0/5.7L). Scheme 371

Note. Fuel system is under pressure. To avoid fuel spillage, refer to field service procedures for testing or making repairs requiring disassembly of fuel lines or fittings.

Flow Chart A7, (2 Of 2) Fuel System Diagnosis (5.0/5.7L). Scheme 372

CHART A9 - COLD START VALVE (ALL ENGINES)

The cold start valve is used to provide additional fuel during the crank mode to improve cold starts. This circuit is important when engine coolant temperature is low because the other injectors are not pulsed on long enough to provide the needed amount of fuel to start.

The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and is protected by a fuse. The system is controlled by a cold start fuel injection switch which provides a ground path for the valve during cranking when engine coolant is below 95°F (35°C).

The cold start fuel injection switch consist of a bi-metallic material which opens at a specified coolant temperature. This bi-metallic spring is also heated by the winding in the thermal switch which allows the valve to stay on for 8 seconds at -4°F (-20°C) coolant. The time the switch will stay closed varies with coolant temperature. In other words, as the coolant temperature goes up, the cold start valve on time goes down.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Disconnecting the distributor 4-way connector will disable the other injectors. The amount of pressure drop depends on the temperature of the engine. This test could also be performed by removing the 2 injector fuses.
2. This test will determine the continuity through the switch to ground.

Flow Chart A9, Cold Start Valve (All Engines). Scheme 373

Flow Chart A9, Cold Start Valve (All Engines, 1 Of 2). Scheme 374

Flow Chart A9, Cold Start Valve (All Engines, 1 Of 2). Scheme 375

CHART C1D - MAP OUTPUT CHECK (ALL ENGINES)

The MAP sensor measures manifold pressure (vacuum) and sends that signal to the ECM. The MAP sensor is mainly used for fuel calculation, when the ECM is running in the throttle body back-up mode. The MAP sensor is also used to determine the barometric vacuum to the sensor. The change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to the MAP hose.

Flow Chart C1D, MAP Output Check (All Engines). Scheme 376

Flow Chart C1D, MAP Output Check (All Engines). Scheme 377

POWER STEERING PRESSURE SWITCH (PSPS) CHECK (ALL ENGINES)

The power steering pressure switch (P/S) opens when P/S pressure goes high, such as on a full turn in either direction. When the P/S switch opens, it turns the A/C relay off, and sends a signal to the ECM. The ECM uses this signal for idle control.

1. A pressure switch that will not close, or an open in circuits No. 901 or 450, may cause the engine to stop when power steering loads are high.
2. A switch that will not open, or a circuit No. 901 shorted to ground, may affect idle quality and will cause the A/C relay to be de-energized.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Different makes of "SCAN" testers may display the state of this switch in different ways. Refer to "SCAN" tester manufacturer operator manuals to determine how this input is indicated.
2. Checks to determine if circuit No. 901 is shorted to ground.
3. This should simulate a closed switch.

Flow Chart C1E, PSPS Check (All Engines). Scheme 378

Flow Chart C1E, PSPS Check (All Engines). Scheme 379

CHART C2C - IDLE AIR CONTROL (IAC) (All ENGINES)

The ECM will control engine idle speed by moving the IAC valve to control air flow around the throttle plate. It does this by sending voltage pulses to the proper motor winding for each IAC motor. This will cause the motor shaft and valve to move in or out of the motor a given distance for each pulse received. The ECM pulses are referred to as counts.

To increase idle speed the ECM will send enough counts to retract the IAC valve and allow more air to flow through the idle air passage and bypass the throttle plate until idle speed reaches the proper RPM. This will increase the ECM counts. To decrease idle speed the ECM will send enough counts to extend the IAC valve and reduce air flow through the idle passage around the throttle plate. This will reduce the ECM counts.

Each time the engine is started and then the ignition is turned off the ECM will reset the IAC valve. This is down by sending enough counts to seat the valve. The fully seated valve is the ECM reference zero. A given number of counts are then calculated by the ECM. This is how the ECM knows what the motor position is for a given idle speed.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Continue with test even if engine will not idle. IF idle is too low, "SCAN" tester will display 80 or more counts, or steps. If idle is high it will display "O" counts. Occasionally an erratic or unstable idle may occur. Engine speed may vary 200 RPM or more up or down. Disconnect IAC. If the condition is unchanged, the IAC is not at fault. There is a system problem. Proceed to DIAGNOSTIC AIDS.
2. When the engine was stopped, the IAC valve retracted (more air) to a fixed "Park" position for increased air flow and idle speed during the next engine start. A "SCAN" tester will display 40 or more counts.
3. Be sure to disconnect the IAC valve prior to this test. The test light will confirm the ECM signals by a steady or flashing light on all circuits.
4. There is a remote possibility that one of the circuits is shorted to voltage which would have been indicated by a steady light. Disconnect ECM and turn the ignition on and probe terminals to check for this condition.

Engine idle speed can be adversely affected by the following

1. If ECM thinks the vehicle is always in neutral, then idle will not be controlled to the specified RPM when in drive range.
2. Leaking injectors will cause fuel imbalance and poor idle quality due to excess fuel. See CHART A7.
3. Vacuum or crankcase leaks can affect idle.
4. When the throttle shaft or throttle position sensor is binding or sticking in an open throttle position, the ECM does not know if the vehicle has stopped and does not control idle.
5. Check air management system for intermittent air to ports while in closed loop.
6. In addition to electrical control of EGR, be sure to examine the EGR valve for proper seating.
7. Faulty battery cables can result in voltage variations. The ECM will try to compensate, which results in erratic idle speeds.
8. The ECM will compensate for A/C compressor clutch loads. Loss of the signal would be most apparent in neutral.
9. Contaminated fuel can adversely affect idle.
10. Perform injector balance test, see CHART C2A. If all is okay, see the CEC TESTS W/O CODES article in this section.

Flow Chart C2C, Idle Air Control (IAC) (All Engines). Scheme 380

Flow Chart C2C, Idle Air Control (IAC) (All Engines). Scheme 381

CHART C3 - CANISTER PURGE CHECK (ALL ENGINES)

Canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when energized. The ECM supplies a ground to energize the solenoid.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks to see if the solenoid is opened or closed. The solenoid is normally energized in this step. It should be closed.
2. This test checks for open or grounded solenoid circuit.
3. Completes functional check by grounding test terminal. This should normally energize the solenoid and allow the vacuum to drop.

Flow Chart C3, Canister Purge Check (All Engines). Scheme 382

Note. This chart only covers the solenoid portion of the Canister Control Purge system. To test the control valve(s), see diagnosis under General Description.

Flow Chart C3, Canister Purge Check (All Engines). Scheme 383

CHART C4A - IGNITION SYSTEM CHECK (5.0/5.7L)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 1) This test checks for proper output from the ignition system. The spark plug tester requires a minimum of 25,000 volts to fire. This check can be used in case of an ignition miss because the DIS system may provide enough voltage to run the engine but not enough to fire a spark plug under heavy load.
2. 1A) If spark occurs with EST connector disconnected, pick-up coil is too low for EST operation.
3. 2) A spark indicates that the problem is a faulty distributor cap or rotor.
4. 3) Normally, there should be battery voltage at the "+" terminal. Low voltage would indicate an open or high resistance circuit from the distributor to coil or ignition switch.
5. 4) This test checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off so normal voltage should be about 12 volts. If the module is turned on, the voltage would be low, but should be above one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the battery to the tachometer terminal.
6. 5) This test checks for an open in the module or the circuit to it. Applying 12 volts to terminal "P" will turn the module on and the voltage should drop to about 7-9 volts.
7. 6) This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil because most module problems would have been found before this point in the test procedure. Using a module tester could determine which is at fault.

Flow Chart C4A, Ignition System Check (5.0/5.7L). Scheme 384

Flow Chart C4A, Ignition System Check (5.0/5.7L, 1 Of 2). Scheme 385

Flow Chart C4A, Ignition System Check (5.0/5.7L, 2 Of 2). Scheme 386

CHART C4B - IGNITION SYSTEM CHECK (2.8L)

Note. Test numbers refer to test numbers on diagnostic chart.

1. 1) This test checks 2 wires, to ensure that an open is not present in a spark plug wire.
2. 1A) If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
3. 2) A spark indicates the problem must be the distributor cap or rotor.
4. 3) There should be battery voltage at terminal "C" and at "+" terminals. Low voltage would indicate an open or a high resistance circuit from the distributor to the coil or ignition switch. If terminal "C" voltage was low, but "+" terminal voltage is 10 volts or more, check circuit from terminal "C" to ignition coil for open or check ignition coil primary winding for open.
5. 4) This test checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off, so normal voltage should be about 12 volts. If the module is turned on, the voltage would be low, but should be above one volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the battery to the tachometer terminal.
6. 5) Applying 1.5-8 volts to module terminal "P" should turn the module on and the tachometer terminal voltage should drop about 7-9 volts. This test will determine whether the module or coil is faulty or if the pick-up coil is not generating the proper signal to turn the module on. This test can be performed by using a DC battery with a rating of 1.5-8 volts. The use of the test light is mainly to allow the terminal "P" to be probed more easily.
7. 5A) Some digital multi-meters can also be used to trigger the module by selecting ohms, usually in the "diode" position. In this position the meter may have a voltage across the terminals which can be used to trigger the module. The voltage in the "ohm" position can be checked by using a second meter or by checking the manufacturer's specification of the tester being used.
8. 6) This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. Use a module tester to determine which is at fault.

Flow Chart C4B, Ignition System Check (2.8L). Scheme 387

Flow Chart C4B, Ignition System Check (2.8L, 1 Of 2). Scheme 388

Flow Chart C4B, Ignition System Check (2.8L, 2 Of 2). Scheme 389

CHART C4F - DIS MISFIRE (2.8L)

The direct ignition system (DIS) uses a waste spark method of distribution. In this type of system, the ignition module triggers the No. 1 and 4 ignition coil pair resulting in both No. 1 and 4 spark plugs firing at the same time. No. 1 cylinder is on the compression stroke at the same time No. 4 cylinder is on the exhaust stroke, resulting in a lower energy requirement to fire No. 4 spark plug. This leaves the remaining high voltage to be used to fire No. 1 spark plug. On this application, the crank sensor is mounted to the engine block and protrudes through the block to within about .050" (1.3 mm) of the crankshaft reluctor. Since the reluctor is a machined portion of the crankshaft and the crank sensor is mounted in a fixed position on the block, timing adjustments aren't possible or necessary.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for voltage output of ignition system. A spark tester must be used, as this tester requires 25,000 volts to trigger. This checks for a potentially weak coil.
2. If the spark tester fires on all wires, the ignition system, with the exception of the spark plugs, may be considered in good working order. If the spark plugs show no evidence of wear, damage or fouling, an engine mechanical fault should be suspected.
3. If the spark jumps the tester gap after grounding the opposite plug wire, it indicates excessive resistance in the spark plug which was by-passed. A faulty or poor connection at that plug could also result in the miss condition. Also check for carbon deposits inside the spark plug boot.
4. If carbon tracking is evident, replace coils and be sure plug wires relating to that coil are clean and tight. Excessive wire resistance or faulty connections could have caused the coil to be damaged.
5. If the no spark condition follows the suspected coil, that coil is faulty. Otherwise, the ignition module is the cause of no spark. This test could also be performed by substituting a known good coil for the one causing the no spark condition.

Flow Chart C4F, DIS Misfire (2.8L Engine). Scheme 390

Flow Chart C4F, DIS Misfire (2.8L Engine). Scheme 391

ELECTRONIC SPARK CONTROL (ESC) CHECK (ALL ENGINES)

The knock sensor is used to detect engine detonation and the ECM will retard the electronic spark timing based on the signal being received. The circuitry within the knock sensor causes the ECM's 5 volts to be pulled down so that under a no knock condition, circuit No. 496 would measure about 2.5 volts. The knock sensor produces an AC signal, which rides on the 2.5 volts DC voltage. The amplitude and frequency are dependent upon the knock level.

The Mem-Cal used with this engine, contains the functions which were part of remotely mounted ESC modules used on other General Motors vehicles. The ESC portion of the Mem-Cal sends a signal to other parts of the ECM which retards the spark timing and reduce detonation.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If a Code 43 is not set, but a knock signal is indicated while running at 1500 RPM, listen for an internal engine noise. Under a no load condition, there should be no detonation, and if knock is indicated, an internal engine problem may exist.
2. Usually a knock signal can be generated by tapping on the right exhaust manifold. This test can also be performed at idle. Test No. 1 was run at 1500 RPM to determine if a constant knock signal was present, which would affect engine performance.
3. This tests whether the knock signal is due to the sensor, a basic engine problem, or the ESC module.
4. If the module ground circuit is faulty, the ESC module will not function correctly. The test light should light indicating the ground circuits are okay.
5. Contacting circuit No. 496, with a test light to 12 volts, should generate a knock signal to determine if it is faulty, or if the ESC module can't recognize a knock signal.

The "SCAN" tester has 2 positions to diagnose the ESC system. The knock signal can be monitored to see if the knock sensor is detecting a knock condition and if the ESC module is functioning. The knock signal should display "yes", whenever detonation is present. The knock retard position on the "SCAN" tester displays the amount of spark retard the ECM is commanding. The ECM can retard the timing up to 20 degrees.

Flow Chart C5, Electronic Spark Control Check (All Engines). Scheme 392

Note. This chart should be used after all other causes of spark knock have been checked, i.e. timing, EGR, engine temperature or excessive engine noise, etc. If Code 43 is set, use that chart first.

Flow Chart C5, Electronic Spark Control Check (All Engines). Scheme 393

CHART C6A - ELECTRIC CONTROL (MAN. TRANS.) (2.8L)

This system uses a single bed converter. Air management is controlled by an air control valve (divert valve). When grounded by the ECM, the solenoid causes the valve to direct air to the exhaust ports. When de-energized, air diverts to the atmosphere. Air will go to the ports, provided the valve has a ground to the ECM and good manifold vacuum.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This is a system performance test. When vehicle goes to "ground loop", air will switch from the ports to the diverter.
2. Tests for a grounded electric diverter circuit. Normal system light will be off.
3. Checks for an open control circuit. Grounding test terminal will energize the solenoid if ECM and circuits are normal. In this test, if test light is on, circuits are normal. Fault is in valve connections or valve.

Flow Chart C6A, Electric Control (Man. Tans.) (2.8L). Scheme 394

Flow Chart C6A, Electric Control (Man. Tans.) (2.8L). Scheme 395

CHART C6B - AIR MANAGEMENT CHECK (5.0/5.7L)

Air management is controlled by a pressure operated port valve and a converter valve, each with an ECM controlled solenoid. When the solenoid is grounded by the ECM, air pressure will activate the valve and allow pump air to be directed as follows

1. Neither solenoid is grounded by the ECM air pump air to atmosphere.
2. Converter solenoid is grounded by the ECM air pump air to converter.
3. Port solenoid is grounded by the ECM air pump air to exhaust ports.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test is a system functional check. Air is directed to ports during "open loop" and all engines start in "open loop" even on a warm engine. Since the air to the ports may be very short, observe port air prior to engine start up. This can be done by squeezing air hose.
2. This should normally set a Code 22. When any code is set, the ECM opens the ground to the converter solenoid and allows air to divert. This checks for ECM response to a fault. A ground in the control valve circuit to the ECM would prevent divert action.
3. This checks for a grounded circuit to the ECM. Test light off is normal and would indicate that the circuit is not grounded.
4. Checks for an open in the solenoid control circuits. Grounding the test terminal should ground both solenoid circuits. Normally, the test light should be on, which indicates the problem is not in the ECM or wiring but at the solenoid connections or valve itself.
5. Checks for a grounded solenoid circuit. Test light off would indicate the circuit is normal and fault is in the valve.

Flow Chart C6B, Air Management Check (5.0/5.7L). Scheme 396

Flow Chart C6B, Air Management Check (5.0/5.7L). Scheme 397

CHART C7 - EGR VALVE CHECK (2.8L)

The integrated electronic EGR valve functions similarly to a port valve with a remote vacuum regulator. The internal solenoid is normally open, which causes the vacuum signal to be vented off to the atmosphere when EGR is not being commanded by the ECM. The EGR valve has a sealed cap and the solenoid valve opens and closes the vacuum signal. This controls the amount of vacuum vented to atmosphere and controls amount of vacuum applied to the diaphragm. The electronic EGR valve contains a voltage regulator, which converts the ECM signal, to provide different amounts of EGR flow by regulating the current to the solenoid. The ECM controls EGR flow with a pulse width modulated signal (turns on and off many times a second). This system also contains a pintle position sensor, which works similarly to a TPS sensor and as EGR flow is increased, the sensor output also increases.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Whenever the solenoid is de-energized, the solenoid valve should be closed, which should not allow the vacuum to move the EGR diaphragm. However, if the filter is plugged, the vacuum applied with the hand held vacuum pump will cause the diaphragm to move because the vacuum will not be vented to the atmosphere.
2. This test will determine if the EGR filter is plugged, or if the EGR valve itself is faulty. Use care when removing the filter, to avoid damaging the EGR assembly.
3. If the valve moves in this test, it is due to circuit No. 435 being shorted to ground.
4. Grounding the diagnostic terminal should energize the solenoid which closes off the vent and allows vacuum to move the diaphragm.
5. The EGR assembly is designed to have some leakage, and therefore 7 in. Hg of vacuum is all that should be held on the assembly. However, if too much of a leak exists (less than 4 in. Hg of vacuum), the EGR assembly is leaking and must be replaced.

The EGR position voltage can be used to determine that the pintle is moving. When no EGR is commanded (0% duty cycle), the position sensor should read between .5-1.5 volts and increase with the commanded EGR duty cycle.

Flow Chart C7, EGR Valve Check (2.8L). Scheme 398

Flow Chart C7, EGR Valve Check (2.8L, 1 Of 2). Scheme 399

Flow Chart C7, EGR Valve Check (2.8L, 2 Of 2). Scheme 400

CHART C7A - EGR CHECK (2.8L)

The EGR valve is controlled by a normally closed solenoid (allows vacuum to pass when energized). The ECM energizes the solenoid to turn the EGR on and monitors vacuum to the EGR with the EGR diagnostic switch. Code 32 will detect a faulty solenoid, vacuum switch or vacuum supply.

Note. Test numbers refer to test numbers on diagnostic chart.

1. With the ignition on and engine stopped, the solenoid should not be energized and vacuum should not pass to the EGR valve.
2. Grounding the diagnostic terminal will energize the solenoid and allow vacuum to pass the valve.
3. Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.
4. The EGR solenoid will not be energized in Park or Neutral. This will determine if the Park/Neutral switch input is being received by the ECM.

Flow Chart C7A, EGR Check (2.8L). Scheme 401

Flow Chart C7A, EGR Check (2.8L, 1 Of 2). Scheme 402

Flow Chart C7A, EGR Check (2.8L, 2 Of 2). Scheme 403

CHART C7B - EGR RECIRCULATION CHECK (5.0/5.7L)

The EGR valve is controlled by a normally open pulse width modulated solenoid (PWM). The ECM turns the solenoid off to allow vacuum to pass to the EGR and turns the solenoid on to prohibit EGR operation. When EGR is commanded, the solenoid is turned on and off many times a second (duty cycle).

The duty cycle is calculated by the ECM based on information from the coolant, MAT, TIPS and MAF sensors. Also, engine RPM and the Park/Neutral switch inputs affect EGR. There is no EGR when in Park or Neutral and TPS is below a calibrated value or TPS is indicating wide open throttle (WOT). With the ignition on and engine stopped, the EGR solenoid is de-energized. The solenoid, however, should be energized if the diagnostic terminal is grounded with the ignition on and engine not running.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This will test the solenoid value to determine if it is capable of closing off the manifold vacuum from the EGR valve. The vacuum may bleed off slowly but this should not be considered a fault.
2. As soon as back pressure is available at the EGR valve, the bleed portion in the valve should open and cause the valve to go to its heated position.
3. The EGR valve will be inoperative if the Park/Neutral switch is misadjusted or defective. Use "SCAN" tester and check Park/Neutral switch.

Flow Chart C7B, EGR Recirculation Check (5.0/5.7L). Scheme 404

Note. Before using this chart, check for ported vacuum to EGR solenoid, also check hoses for leaks and restrictions. Should be at least 7" Hg vacuum at 2000 RPM. This chart assumes there is no Code 32.

Flow Chart C7B, EGR Recirculation Check (5.0/5.7L). Scheme 405

TRANSMISSION CONVERTER CLUTCH (TCC) (ALL 2.8L)

The purpose of the transmission converter clutch feature is to eliminate the power loss of the transmission converter stage when the vehicle is in a cruise condition. This allows the convenience of the automatic transmission and the fuel economy of a manual transmission. Electrical power from the ignition circuit is supplied to the TCC solenoid through the brake switch and transmission 3rd gear switch. The ECM will engage TCC by grounding circuit No. 422 to energize the solenoid.

Note. Test numbers refer to test numbers on diagnostic chart.

1. If test light is off this confirms 3rd gear switch is open.
2. At 25 MPH, the 3rd gear switch should close. Test light will come on and confirm battery supply and closed brake switch.
3. Grounding the diagnostic terminal with ignition on and engine off should energize the TCC solenoid by grounding circuit No. 422. This test checks the ability of the ECM to supply a ground to the TCC solenoid. The test light connected from 12 volts to ALDL terminal "F" will turn on as circuit No. 422 is grounded.

The "SCAN" tester only indicates when the ECM has turned on the TCC driver and this does not confirm that the TCC has engaged. To determine if TCC is functioning properly, engine RPM should decrease when the "SCAN" tester indicates the TCC driver has turned on.

Flow Chart C8A, TCC (All 2.8L). Scheme 406

Using A Scan Tool, Check The Following And Correct If Necessary

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Should Indicate VSS With Wheels Turning
4. Codes - If 24 Is Present, See Code Chart 24

Flow Chart C8A, TCC (All 2.8L). Scheme 407

TRANSMISSION CONVERTER CLUTCH (TCC) (2.8L "F" BODY)

The purpose of the automatic transmission torque converter clutch feature is to eliminate power loss of the torque converter when the vehicle is in a cruise condition. This allows the convenience of an automatic and the fuel economy of a manual transmission. The heart of the system is a solenoid located inside the transmission, which is controlled by the ECM.

When the solenoid coil is activated, the torque converter clutch is applied, which results in straight through mechanical coupling from the engine to the wheels. When the transmission solenoid is deactivated, the torque converter clutch is released, which allows the torque converter to operate in the conventional manner (fluidic coupling between engine and transmission).

The transmission converter clutch will engage when the following conditions occur

1. Engine is warmed up.
2. Vehicle speed is above a calibrated value.
3. Throttle position sensor output is not changing, indicating a steady road speed.
4. Brake switch is closed.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks the continuity of the TCC circuit from the fuse to the ALDL connector.
2. When the brake pedal is released, the light should come back on and then go off when the diagnostic terminal is grounded. This will test circuit No. 422 and the TCC drive in the ECM.

The "SCAN" tester only indicates when the ECM has turned on the TCC driver, and this does not confirm that the TCC has engaged. To determine if TCC is functioning properly, engine RPM should decrease when the "SCAN" tester indicates the TCC driver has turned on.

Flow Chart C8B, TCC (2.8L "F" Body). Scheme 408

Using A Scan Tool Check The Following And Correct If Necessary

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Be Sure Scan Displays VSS With Drive Wheels Turning
4. Codes - If Code 24 Is Present, See Code Chart 24

Flow Chart C8B, TCC (2.8L "F" Body). Scheme 409

TRANSMISSION CONVERTER CLUTCH (TCC) (2.8L "A" BODY)

The 3rd gear switch is open both in 3rd and 4th gear. The 4th gear switch is open only in 4th gear, which allows for TCC when in 4th gear. The TCC will disengage during a 4-3 downshift.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Some "SCAN" testers display the state of these switches in different ways. Be familiar with the type of tester being used. Since both switches should be in the closed state during this test, the tester should read the same for either the 3rd or 4th gear switch.
2. Determines whether the switch or signal circuit is open. The circuit can be checked for an open by measuring the voltage (with a voltmeter) at the TCC connector. Should be about 12 volts.
3. Because the switch should be grounded in this step, disconnecting the TCC connector should cause the "SCAN" switch state to change.
4. The switch state should change when the vehicle shifts into 3rd gear.

If vehicle is road tested because of a TCC related problem, be sure the switch states do not change while in 4th gear because the TCC will disengage. If switches change state, carefully check wire routing and connections.

Flow Chart C8B, TCC (2.8L "A" Body). Scheme 410

Note. Checks performed in this chart will not prevent the TCC from working, but will affect engagement or disengagement points.

Flow Chart C8B, TCC (2.8L "A" Body). Scheme 411

TRANSMISSION CONVERTER CLUTCH (TCC) (5.0/5.7L) (1 OF 2)

The purpose of the automatic transmission torque converter clutch feature is to eliminate the power loss of the torque converter stage when the vehicle is in a cruise condition. This allows the convenience of the automatic transmission and the fuel economy of a manual transmission. The heart of the system is a solenoid located inside the automatic transmission which is controlled by the ECM.

When the solenoid coil is activated (on), the torque converter clutch is applied through a mechanical coupling from the engine to transmission. When the transmission solenoid is deactivated, the torque converter clutch is released which allows the torque converter to operate in the conventional manner (fluid coupling between engine and transmission). The ECM turns on the TCC when coolant temperature is above 149°F (65°C), TPS is not changing and vehicle speed is above a specified value.

Note. Test numbers refer to test numbers on diagnostic chart.

1. When a test light is connected from ALDL terminal "F" to ground, a test light on indicates battery voltage is okay and the TCC solenoid is disengaged.
2. When the diagnostic terminal is grounded, the ECM should energize the TCC solenoid and the test light should go out.

A "SCAN" tester only indicates when the ECM has turned on the TCC driver (grounded circuit No. 422) but this does not confirm that the TCC has engaged. To determine if TCC is functioning properly, engine RPM should decrease when the "SCAN" tester indicates the TCC driver has turned on. The switches will not prevent TCC from functioning but will affect TCC lock and unlock points. If the 4th gear switch circuit is always open the TCC may engage as soon as sufficient oil pressure is reached.

Flow Chart C8A (1 Of 2), TCC (5.0/5.7L). Scheme 412

Using A "Scan" Tool, Check The Following & Correct If Necessary

1. Coolant Temperature Should Be Above 65°C
2. TPS - Be Sure TPS Signal Is Not Erratic
3. VSS - Be Sure "Scan" Displays VSS With Drive Wheels Turning, If Code 24 Is Present, See Code Chart 24

Flow Chart C8A (1 Of 2), TCC (5.0/5.7L). Scheme 413

TRANSMISSION CONVERTER CLUTCH (TCC) (5.0/5.7L) (2 OF 2)

A 4th gear switch (mounted in the transmission) opens when the transmission shifts into 4th gear and this switch is used by the ECM to modify TCC lock and unlock points (when in a 4-3 downshift).

Note. Test numbers refer to test numbers on diagnostic chart.

1. Unless the switch or circuit No. 446 is open, the "SCAN" tester should display "NO", indicating the transmission is not in 4th gear. The 4th gear switch should only be open while in 4th gear.
2. This test determines if the ECM and wiring are okay. Grounding circuit No. 446 should cause the "SCAN" tester to display "NO", indicating the transmission is not in 4th gear.
3. Checks the operation of the 4th gear switch. When the transmission shifts into 4th gear the switch should open and the "SCAN" tester should display "YES".
4. Disconnecting the TCC connector simulates an open switch to determine if circuit No. 446 is shorted to ground or the problem is in the transmission.

A road test may be necessary to verify the problem. If the "SCAN" tester indicates TCC is turning on and off erratically, check the state of the 4th gear switch to be sure it is not changing under a steady throttle position. If the switch is changing, check connections and wire routing carefully. If the 4th gear switch is always open the TCC may engage as soon as sufficient oil pressure is reached.

Flow Chart C8A (2 Of 2), TCC (5.0/5.7L). Scheme 414

Note. Checks made in this chart will not prevent the TCC from working, but will affect engagement or disengagement points.

Flow Chart C8A (2 Of 2), TCC (5.0/5.7L). Scheme 415

CHART C8B - MAN. TRANS. SHIFT LIGHT (5.0/5.7L)

The shift light indicates the best transmission shift point for maximum fuel economy. The light is controlled by the ECM and is turned on by grounding circuit No. 456. The ECM uses information from the following inputs to control the shift light

1. Coolant temperature
2. TPS
3. VSS
4. RPM

The ECM uses the measured RPM and the vehicle speed to calculate what gear the vehicle is in. This calculation determines when the shift light should be turned on.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test should not turn on the shift light. If the light is on, there is a short to ground in circuit No. 456 wiring or a fault in the ECM.
2. When the diagnostic terminal is grounded, the ECM should ground circuit No. 456 and the shift light should come on.
3. This checks the shift light circuit up to the ECM connector. If the shift light illuminates, then the ECM connector is faulty or the ECM does not have the ability to ground the circuit.

Flow Chart C8B, Manual Transmission Shift Light (5.0/5.7L). Scheme 416

Flow Chart C8B, Manual Transmission Shift Light (5.0/5.7L). Scheme 417

CHART C10 - A/C CLUTCH CONTROL (2.8L)

The ECM control of the A/C clutch improves idle quality and performance by the following conditions

1. Delaying clutch application until idle air rate is increased.
2. Releasing clutch when idle speed is too low or during high power steering loads.
3. Releasing clutch at wide open throttle (WOT).
4. Smooths cycling of the compressor by providing additional fuel at the instant clutch is applied.

Voltage is supplied to the A/C clutch control relay on circuit No. 59 by the A/C control switch. This same voltage is supplied as a signal to ECM pin No. "B8". After a time delay of about a 1/2 second the ECM will ground terminal "A2", circuit No. 905 and close the A/C relay contacts. When the relay is energized by battery voltage from circuit No. 59. a signal is sent to the A/C clutch through the A/C clutch relay and circuit No. 959.

Note. Test numbers refer to test numbers on diagnostic chart.

1. The ECM will only energize the A/C relay when the engine is running. This test will determine if the relay or circuit No. 905 is faulty.
2. In order for the clutch to properly be engaged, the pressure cycling switch must be closed to provide 12 volts to the relay and the high pressure switch must be closed, so the A/C request (12 volts) will be present at the ECM.
3. Determines if the signal is reaching the ECM on circuit No. 59 from the A/C control panel. Signal should only be present when the A/C mode or defrost mode has been selected.
4. A short to ground in any part of the A/C request circuit No. 67, A/C clutch relay circuits No. 59 and 959, or the A/C clutch could be the cause of the blown fuse.
5. With the ignition on and the diagnostic terminal grounded, the ECM should be grounding circuit No. 905, which should cause the test light to be on.

If problem is insufficient cooling, this may be caused by an inoperative cooling fan. The engine cooling fan should turn on when A/C is on and A/C head pressure exceeds about 233 psi (16.4 kg/cm 2 ). If not, see CHART C12 below for diagnosing the cooling fan.

Flow Chart C10, A/C Clutch Control (2.8L Engine). Scheme 418

Flow Chart C10, A/C Clutch Control (2.8L Engine, 1 Of 2). Scheme 419

Flow Chart C10, A/C Clutch Control (2.8L Engine, 1 Of 2). Scheme 420

CHART C12 - COOLING FAN CONTROL CIRCUIT (2.8L) (1 OF 2)

The electric cooling fan is controlled by the ECM, based on inputs from the coolant temperature sensor, the A/C fan control switch, and vehicle speed sensor. The ECM controls the fan by grounding circuit No. 335, which energizes the fan control relay. Battery voltage is then supplied to the fan motor.

The ECM grounds circuit No. 335, when coolant temperature is over about 223°F (106°C), or when A/C has been turned on. This will cause the fan control switch to open with high A/C pressure, about 200 psi (13.8 kg/cm 2 ). Once the ECM turns the relay on, it will keep it on for a minimum of 30 seconds, or until vehicle speed exceeds 70 MPH. Also, if Code 14 or 15 sets, or the ECM is in throttle body back up, the fan will run at all times. On a vehicles not equipped with A/C, circuit No. 732 is jumpered to ground so that the fan does not run at all times.

Note. Test numbers refer to test numbers on diagnostic chart.

1. With the diagnostic terminal grounded, the cooling fan control driver will close, which should energize the fan control relay.
2. If the A/C fan control switch or circuit is open, the fan would run whenever the engine is running.
3. With the A/C clutch engaged, the A/C fan control switch should open when A/C high pressure exceeds about 200 psi (13.8 kg/cm 2 ). This signal should cause the ECM to energize the fan control relay.

If the problem is overheating, it must be determined if the overheating was due to an actual boil over, hot light or the temperature gauge indicating overheating.

If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using the "SCAN" tester and comparing its reading with the gauge reading.

If the engine is actually overheating, and the gauge indicates overheating, but the cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced. If the engine is overheating and the cooling fan is on, the cooling system should be checked.

Flow Chart C12 (1 Of 2), Cooling Fan Control Circuit (2.8L). Scheme 421

Flow Chart C12 (1 Of 2, Part 1), Cooling Fan Control Circuit (2.8L). Scheme 422

Flow Chart C12 (1 Of 2, Part 2), Cooling Fan Control Circuit (2.8L). Scheme 423

CHART C12 - COOLING FAN CONTROL CIRCUIT (2.8L) (2 OF 2)

Note. Test numbers refer to test numbers on diagnostic chart.

1. There should be 12 volts available to both terminals "E" and "C", when the ignition is on.
2. This test checks the ability of the ECM to ground circuit No. 335. The SES light should also be flashing at this point. If it isn't flashing see CHART A2.
3. If the cooling fan does not turn on at this point, circuit No. 936 or circuit No. 150 has an open, or the cooling fan motor is faulty.

Flow Chart C12 (2 Of 2), Cooling Fan Control Circuit (2.8L). Scheme 424

Flow Chart C12 (2 Of 2), Cooling Fan Control Circuit (2.8L). Scheme 425

CHART C12 - COOLING FAN CONTROL CIRCUIT (5.0/5.7L) (1 OF 2)

The cooling fan is totally controlled by the ECM based on inputs from the coolant sensor and fan control switch. The fan should run, if coolant temperature is more than 221°F (105°C). Battery voltage is supplied to the fan relay on terminal "E" and ignition voltage to terminal "C".

Grounding circuit No. 335 (relay terminal "B") will energize the relay and supply battery voltage to the fan motor. Once the fan relay is energized by the ECM, it will remain on for a minimum of 5 seconds. The ECM will remove the ground to circuit No. 335, if vehicle speed is over 40 MPH or the engine is overheating.

The fan control switch is mounted in the A/C high pressure line and will open when head pressure exceeds 233 psi (16 kg/cm 2 ) and this input causes the ECM to ground circuit No. 335. On a vehicle without A/C, circuit No. 732 is connected to ground to prevent the cooling fan from operating at all times. If Code 14 or 15 sets or the ECM is operating in the fuel back-up mode the ECM will turn on the cooling fan.

If there is a overheating problem, it must be determined if the complaint was due to an actual boil over or if the hot light or temperature gauge indicates overheating.

If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. The gauge accuracy can also be checked by comparing the coolant sensor reading using a "SCAN" tester and comparing it's reading with the gauge reading.

If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced. If the engine is overheating and the cooling fan is on, the cooling system should be checked.

Flow Chart C12 (1 Of 2), Cooling Fan Control Ckt (5.0/5.7L). Scheme 426

Flow Chart C12 (1 Of 2, Part 1), Cooling Fan Control Ckt (5.0/5.7L). Scheme 427

Flow Chart C12 (1 Of 2, Part 2), Cooling Fan Control Ckt (5.0/5.7L). Scheme 428

CHART C12 - COOLING FAN CONTROL CIRCUIT (5.0/5.7L) (2 OF 2)

The cooling fan is totally controlled by the ECM based on inputs from the coolant sensor and fan control switch. The fan should run if coolant temperature is more than 221°F (105°C). Battery voltage is supplied to the fan relay on terminal "E" and ignition voltage to terminal "C".

Grounding circuit No. 335 (relay terminal "B") will energize the relay and supply battery voltage to the fan motor. Once the fan relay is energized by the ECM, it will remain on for a minimum of 5 seconds. The ECM will remove the ground to circuit No. 335 if vehicle speed is over 40 MPH unless the engine is overheating.

The fan control switch is mounted in the A/C high pressure line and will open when head pressure exceeds 233 psi (16 kg/cm 2 ). This input causes the ECM to ground circuit No. 335. On a vehicle without A/C, circuit No. 732 is connected to ground to prevent the cooling fan from operating at all times. If Codes 14 or 15 sets or the ECM is operating in the fuel back-up mode the ECM will turn on the cooling fan. For code testing procedures, refer to the V6/V8 PFI TESTS/CODES article in this section.

If there is a problem of overheating, it must be determined if the problem was due to actual boil over or if the hot light or temperature gauge indicated overheating.

If the gauge or light indicates overheating, but no boil over is detected, the gauge circuit should be checked. the gauge accuracy can also be checked by comparing the coolant sensor reading using the "SCAN" tester and comparing its reading with the gauge reading.

If the engine is actually overheating and the gauge indicates overheating, but the cooling fan is not coming on, the coolant sensor has probably shifted out of calibration and should be replaced. If the engine is overheating and the cooling fan is on, the cooling system should be checked.

Flow Chart C12 (2 Of 2), Cooling Fan Control Ckt (5.0/5.7L). Scheme 429

Flow Chart C12 (2 Of 2), Cooling Fan Control Ckt (5.0/5.7L). Scheme 430

PFI Component Location (2.8L A Body). Scheme 431

PFI Component Location (2.8L F Body). Scheme 432

PFI Component Location (2.8L P Body). Scheme 433

PFI Component Location (5.0L & 5.7L). Scheme 434

PFI ECM Terminal ID (2.8L Except Fiero). Scheme 435

PFI ECM Terminal ID (2.8L Fiero). Scheme 436

PFI ECM Terminal ID (5.0L & 5.7L). Scheme 437

PFI Wiring Diagram (2.8L Beretta & Corisca 2.8L). Scheme 438

PFI Wiring Diagram (2.8L Camaro & Firebird). Scheme 439

PFI Wiring Diagram (2.8L Cavalier & Firenza). Scheme 440

PFI Wiring Diagram (2.8L Century, Celebrity, Ciera & 6000). Scheme 441

PFI Wiring Diagram (2.8L Fiero). Scheme 442

PFI Wiring Diagram (5.0L & 5.7L Camaro & Firebird). Scheme 443

PFI Wiring Diagram (5.7L Corvette). Scheme 444