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Engine Control System - Basic Engine Testing Pontiac Trans Sport II

Testing & Diagnostics ~4741 words

INTRODUCTION

The following diagnostic steps help prevent overlooking simple problems. This is also where to begin diagnosis for no-start condition.

The first step in diagnosing any driveability problem is verifying the customer's complaint by test driving vehicle under the conditions in which the problem reportedly occurred.

Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.

Note. Unless otherwise instructed in test procedures, perform all voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.

System Or ComponentDiagnostic Information Location
Malfunction Indicator Light (MIL)See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
DLC & MIL On SteadySee ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
No Scan Tool DataSee ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
No-Start DiagnosisSee NO START - ENGINE CRANKS OKAY
Injector Circuit DiagnosisSee BASIC FUEL SYSTEM CHECKS
Fuel Pump RelaySee MODULES, MOTORS, RELAYS & SOLENOIDS in SYSTEM/COMPONENT TESTS article
Fuel System DiagnosisSee BASIC FUEL SYSTEM CHECKS
Injector Balance TestSee FUEL SYSTEM in SYSTEM/COMPONENT TESTS article
MAP SensorSee ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article
Transmission Range SwitchSee ENGINE SENSORS & SWITCHES in SYSTEM/COMPONENT TESTS article
IAC ValveSee IDLE CONTROL SYSTEM under FUEL SYSTEM in SYSTEM/COMPONENT TESTS article
Fuel Evaporation ControlSee EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article
Ignition Control CircuitSee IGNITION SYSTEM in SYSTEM/COMPONENT TESTS article
Knock Sensor CheckSee IGNITION SYSTEM in SYSTEM/COMPONENT TESTS article
EGR SystemSee EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article
Torque Converter Clutch(1) See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article
Manual Trans. Shift Lights(1) See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article
A/C Clutch ControlSee MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article
Elec.Cooling Fan Control(2) See MISCELLANEOUS PCM/VCM CONTROLS in SYSTEM/COMPONENT TESTS article
(1) Complete coverage in TRANSMISSION SERVICING article. (2) Covered in entirety in A/C-HEATER SYSTEM article.
(1)Complete coverage in TRANSMISSION SERVICING article.
(2)Covered in entirety in A/C-HEATER SYSTEM article.

GENERAL MOTORS REFERENCE

VISUAL INSPECTION

Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see VACUUM DIAGRAMS article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Compression

Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see the SPECIFICATIONS article.

WARNINGBecause fuel injectors on many models are triggered by ignition switch during cranking mode, DO NOT use ignition switch during compression tests. Use a remote starter to crank engine to prevent fire hazard or engine's oiling system contamination.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (0-5 psi) gauge to check exhaust system.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Partially open throttle and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.

If using a low pressure gauge, connect gauge in the following manner

  1. Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.

Diagnosis

  1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
  2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as required.

NO-START DIAGNOSIS

Note. For terminal and circuit ID, see the WIRING DIAGRAMS article.

DEFINITION

No-start is defined as engine cranks okay but does not start. Engine may fire a few times.

NO START - ENGINE CRANKS OKAY

Note. Before performing following tests, check battery condition, engine cranking speed and fuel supply.

General Inspection

  1. Ensure proper starting procedure is being used. Visually check vacuum hoses for splits, kinks and proper connections, as shown on Vehicle Emission Control Information label. Check ignition wires for cracking, hardness and proper connections at both coil pack and spark plugs.
  2. Remove spark plugs. Check and replace as necessary. In very cold temperatures, ensure oil is proper viscosity and not contaminated with gasoline.

Ignition System

  1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
  2. Install Tech 1 scan tool. Using scan tool, select FAILED SINCE CODE CLEAR function. If Diagnostic Trouble Code (DTC) P0101, P0123, P0601/P0602, P1200, P1374, P1626 or P1629 is present, diagnose DTC. See the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article. If DTC(s) are not present, go to next step.
  3. Turn ignition on with engine off. Using scan tool, monitor Manifold Absolute Pressure (MAP) sensor. If MAP sensor value is less than 65 kPa, go to step 27). If MAP sensor value is more than 65 kPa, go to next step.
  4. Turn ignition off. Disconnect MAP sensor connector. Attempt to start engine. If engine starts and continues to run, go to step 27). If engine does not start, go to next step.
  5. Turn ignition off. Reconnect MAP sensor connector. Install fuel pressure gauge. Turn ignition on and observe fuel pressure. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is as specified, go to step 7). If fuel pressure is not as specified, go to next step.
  6. If fuel pressure is present, but not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing) . If fuel pressure is not present, go to FUEL SYSTEM.
  7. Turn ignition off. Disconnect 10-pin fuel injector/engine harness connector. Using a test light connected to battery voltage, probe each injector driver circuit while cranking engine. If test light flashes, go to next step. If test light does not flash, go to step 9).
  8. Remove fuel injection fuse from underhood fuse block. Install Spark Tester (J-26792) to cylinder No. 2, 4 and 6 (one at a time). Connect the spark plug wire of companion cylinder to ground. Crank engine and observe spark tester. If spark is present, go to step 19). If spark is not present, go to step 11).
  9. Check fuel injector feed circuit fuse. If fuse is faulty, check for an open or shorted circuit, or shorted injector. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuit and injector are okay, go to next step.
  10. Check for open in fuel injector feed circuit or ignition main relay feed circuits. Check for open in ignition main relay ground circuit. Check for stuck open ignition main relay or corroded contacts. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuits or relay are okay, testing is complete.
  11. Check fuse to Ignition Control Module (ICM) ignition feed circuit. If fuse is faulty, check for short between ICM feed circuit and engine ground, module ground, IC control circuit or reference low circuit. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If fuse is okay, go to next step.
  12. Check for open in ICM feed and ground circuits. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuits are okay, go to next step.
  13. Disconnect 7X Crankshaft Position (CKP) sensor connector from ICM. Connect DVOM between CKP sensor harness connector terminals. Set DVOM to 2-volt AC scale. Crank engine and observe DVOM. DVOM should read about 2-volts AC. If voltage is as specified, go to step 15). If voltage is not as specified, go to next step.
  14. Turn ignition off. Check 7X CKP sensor circuit for open or short to voltage or ground. Check for poor 7X CKP sensor connection. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuit is okay, go to step 28).
  15. Check for poor ICM connection. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If connection is okay, go to next step.
  16. Remove and inspect coil that did not produce a spark. Check for cracks or carbon tracking. Replace as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If coil(s) are okay, go to next step.
  17. Check secondary resistance to ignition coil that did not produce a spark. Resistance should be 5000-7000 ohms. If resistance is not as specified, replace ignition coil. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If coil resistance is as specified, go to next step.
  18. Connect a test light across affected ICM primary terminals. Crank engine and observe test light. If test light flashes while cranking engine, go to step 29). If test light does not flash, go to step 30).
  19. Check cylinders No. 2, 4 and 6 spark plug wires. Check for carbon tracking or damaged insulation. Replace as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If wire(s) are okay, go to next step.
  20. Check spark plug wire resistance of cylinders No. 2, 4 and 6. Resistance should be 7000 ohms. If resistance is not as specified, replace wire(s). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If wire(s) are okay, go to next step.
  21. Remove spark plugs from cylinders No. 2, 4 and 6. Check spark plug electrodes for excessive fouling. If excessive fouling is present, go to step 26). If excessive fouling is not present, go to next step.
  22. Check cylinders No. 1, 3 and 5 spark plug wires. Check for carbon tracking or damaged insulation. Replace as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If wire(s) are okay, go to next step.
  23. Check spark plug wire resistance of cylinders No. 1, 3 and 5. Resistance should be 7000 ohms. If resistance is not as specified, replace wire(s). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If wire(s) are okay, go to next step.
  24. Remove spark plugs from cylinders No. 1, 3 and 5. Check spark plug electrodes for excessive fouling. If excessive fouling is present, go to step 26). If excessive fouling is not present, go to next step.
  25. Test fuel for contamination. If fuel is contaminated, clean fuel system. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If fuel is not contaminated, check for poor or damaged PCM connector, for faulty engine coolant temperature sensor, or mass air flow miscalculated due to faulty throttle position sensor or manifold absolute pressure sensor. See the «SYSTEM/COMPONENT TESTS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) article.
  26. Check for engine mechanical problem. Check for bent push rods, faulty camshaft, leaking or sticky valves or rings, excessive valve deposits, loose or worn rocker arms, weak valve springs, incorrect valve timing or leaking head gasket. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  27. Replace MAP sensor. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  28. Replace 7X CKP sensor. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  29. Replace ignition coil(s) associated with cylinder that did not produce a spark. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  30. Replace ICM. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  31. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .

Fuel System

  1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
  2. Turn ignition off. Install fuel pressure gauge to fuel pressure test port. Connect a fused jumper wire between battery voltage and fuel pump test terminal. Note fuel pressure. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 10).
  3. Disconnect jumper wire from fuel pump test terminal. Remove fuel pump relay. Connect a test light between fuel pump relay harness connector terminals No. 87 (Red wire) and No. 85 (Black/White wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
  4. Turn ignition off. Connect a test light between fuel pump relay harness connector terminals No. 86 (Dark Green/White wire) and No. 85 (Black/White wire). Turn ignition on. Test light should illuminate for about 2 seconds. If test light illuminates as specified, go to step 8). If test light does not illuminate or stays illuminated for greater than 2 seconds, go to next step.
  5. Turn ignition off. Disconnect PCM harness connector. Using a test light connected to battery voltage, probe fuel pump relay circuit (Dark Green/White wire) at PCM connector. If test light illuminates, go to step 15). If test light does not illuminate, go to next step.
  6. Check for continuity in fuel pump relay circuit between PCM and fuel pump relay. If circuit is open, repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuit is okay, go to next step.
  7. Check fuel pump relay circuit for poor terminal connection at PCM. Replace as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If terminal connection is okay, go to step 20).
  8. Check for poor terminal connection at fuel pump relay. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If connection is okay, go to step 18).
  9. Using test light connected to ground, probe battery feed circuit (Red wire) at fuel pump relay harness connector. If test light illuminates, go to step 17). If test light does not illuminate, go to step 16).
  10. Remove fuel filler cap and listen for fuel pump operation. If fuel pump is operating, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing) . If fuel pump is not operating, go to next step.
  11. Raise vehicle (leave fuel pump circuit jumpered). Disconnect fuel pump harness connector. Connect a test light between fuel pump harness connector terminals. If test light illuminates, go to step 19). If test light does not illuminate, go to next step.
  12. Connect test light to chassis ground. Probe fuel pump harness connector terminal (Gray wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
  13. Locate and repair open in fuel pump ground circuit (Black wire). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  14. Locate and repair open in fuel pump feed circuit (Gray wire). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  15. Locate and repair short to ground in fuel pump relay PCM feed circuit (Dark Green/White wire). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  16. Locate and repair open in ignition feed to fuel pump relay circuit (Red wire). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  17. Locate and repair open in ground circuit to fuel pump relay (Black/White wire). After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  18. Replace fuel pump relay. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  19. Replace fuel pump. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  20. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .

FUEL SYSTEM PRESSURE RELIEF

WARNINGBegin fuel system trouble shooting and diagnosis with fuel system pressure test. Relieve fuel system pressure before disconnecting any components or installing fuel pressure gauge.

Fuel system is under pressure, which must be relieved before servicing fuel system.

Fuel pressure may be relieved by the following method

  1. Disconnect negative battery cable. Loosen fuel filler cap. Install Fuel Pressure Gauge (J-34730-1A) to fuel pressure test head. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Place gauge bleed hose in container. Open bleed valve to relieve fuel pressure.

FUEL SYSTEM PRESSURE TEST

WARNINGBegin fuel system trouble shooting and diagnosis with fuel system pressure test. Relieve fuel system pressure before disconnecting any components or installing fuel pressure gauge.
  1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
  2. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__fuel-system-pressure-relief) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure connector. Turn ignition on with engine off. With fuel pump running, fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 12).
  3. Wait for fuel pump to stop running. Observe fuel pressure after 10 minutes. Fuel pressure should remain within 5 psi (.35 kg/cm 2 ) of specified pressure. If pressure drops more than 5 psi (.35 kg/cm 2 ), go to step 10). If pressure remains within 5 psi (.35 kg/cm 2 ) of specified pressure, go to next step.
  4. Relieve fuel pressure until pressure is 10 psi (.7 kg/cm 2 ). Observe fuel pressure after 10 minutes. Fuel pressure should remain within 2 psi (.14 kg/cm 2 ) of specified pressure. If pressure drops more than 2 psi (.14 kg/cm 2 ), go to step 19). If pressure remains within 2 psi (.14 kg/cm 2 ) of specified pressure, go to next step.
  5. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to next step. If fuel pressure is as specified, go step 8).
  6. Inspect fuel filter and fuel supply line. Repair or replace as necessary. After repairs, go to step 24). If fuel filter and fuel supply line are okay, go to next step.
  7. Remove fuel sending unit from fuel tank. Inspect fuel pump strainer for restriction, position of fuel pump strainer, fuel pump flex pipe for leaks, or verify if fuel pump is of right application. Repair or replace as necessary. After repairs, go to step 24). If no problems are found, go to step 19).
  8. Turn ignition off for 10 seconds. Turn ignition on. Start and warm engine to normal operating temperature. Allow engine to idle. Observe fuel pressure gauge. Fuel pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). If fuel pressure drop is as specified, see the «TESTS W/O CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wo-codes) article. If fuel pressure drop is not as specified, go to next step.
  9. Disconnect vacuum hose to fuel pressure regulator. With engine at idle, apply 12-14" Hg vacuum to fuel pressure regulator, using a vacuum pump. Fuel pressure should drop 3-10 psi (.2-.7 kg/cm 2 ). If fuel pressure drop is as specified, go to step 20). If fuel pressure drop is not as specified, go to step 21).
  10. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__fuel-system-pressure-relief) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure connector. Install Fuel Pipe Shut-Off Adapter (J-37287) between fuel feed line and return line. Open valve on shut-off adapter. Using scan tool, pressurize fuel system. Bleed air out of fuel gauge. Wait for pressure to build up. Close valve in fuel shut-off adapter. If fuel pressure remains constant, go to step 19). If fuel pressure does not remain constant, go to next step.
  11. Open fuel shut-off adapter valve. Using scan tool, pressurize fuel system. Wait for pressure to build up. Close shut-off valve. If fuel pressure remains constant, go to step 21). If fuel pressure does not remain constant, go to step 22).
  12. If fuel pressure is greater than 47 psi (3.3 kg/cm 2 ), go to next step. If fuel pressure is less than 47 psi (3.3 kg/cm 2 ), go to step 15).
  13. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__fuel-system-pressure-relief) . Disconnect fuel return line from fuel rail. Attach a piece of fuel hose to return line and place in a container. Turn ignition off for about 10 seconds. Turn ignition on. Observe fuel pressure with fuel pump operating. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is as specified, go to step 23). If fuel pressure is not as specified, go to next step.
  14. Inspect fuel rail return/outlet passage for restriction. If restriction is present, go to step 24). If restriction is not present, go to step 21).
  15. If fuel pressure is not present, go to next step. If fuel pressure is present, go to step 17). CAUTION: DO NOT allow fuel pressure to exceed 65 psi (4.5 kg/cm 2 ).
  16. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__fuel-system-pressure-relief) . Connect Fuel Pressure Gauge (J-34730-1A). Install Fuel Pipe Shut-Off Adapter (J-37287) between fuel feed line and return line. Open valve on shut-off adapter. Using scan tool, pressurize fuel system. Bleed air out of fuel gauge. Wait for pressure to build up. Slowly close valve on fuel shut-off adapter. Fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure increases to greater than specification, go to step 21). If fuel pressure does not increase to greater than specification, go to step 7).
  17. Check fuel system electrical circuits. See FUEL SYSTEM under «NO-START DIAGNOSIS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__no-start-diagnosis) . If fuel pump circuit is faulty, go to step 24). If fuel pump circuit is okay, go to next step.
  18. Inspect fuel filter for obstruction, fuel supply line for restriction, fuel pump strainer for correct installation, fuel pump strainer for obstructions or fuel pump flex pipe for leaks. Repair or replace as necessary. After repairs, go to step 24). If problem was not found, go to next step.
  19. Replace fuel sending unit. After repairs, go to step 25).
  20. Locate and repair vacuum leak to fuel pressure regulator. After repairs, go to step 25).
  21. Replace fuel pressure regulator. After repairs, go to step 25).
  22. Locate and replace and leaking fuel injector(s). After repairs, go to step 25).
  23. Locate and correct restriction in fuel return line. After repairs, go to step 25).
  24. Repair problem as necessary. After repairs, go to step 25).
  25. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__fuel-system-pressure-relief) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure connector. Turn ignition on with engine off. With fuel pump running, fuel pressure should be 41-47 psi (2.9-3.3 kg/cm 2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 11).
  26. Wait for fuel pump to stop running. Observe fuel pressure after 10 minutes. Fuel pressure should remain within 5 psi (.35 kg/cm 2 ) of specified pressure. If pressure drops more than 5 psi (.35 kg/cm 2 ), go to step 10). If pressure remains within 5 psi (.35 kg/cm 2 ) of specified pressure, system is okay.

BASIC IGNITION SYSTEM CHECKS

Note. To diagnose ignition system, see appropriate IGNITION SYSTEM test in NO-START DIAGNOSIS .

IDLE SPEED & IGNITION TIMING

Ensure idle speed and ignition timing are set to specifications. For specifications, see SPECIFICATIONS article. For adjustment procedures, see ADJUSTMENTS article.

ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK

Note. Use of Tech 1 scan tool is required to perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK .

The OBD System Check determines

  1. If Malfunction Indicator Light (MIL) works.
  2. If PCM/VCM is operating and can recognize a fault.
  3. If any Diagnostic Trouble Codes (DTCs) are stored.

After performing procedures in PRELIMINARY INSPECTION & ADJUSTMENTS, BASIC FUEL SYSTEM CHECKS and BASIC IGNITION SYSTEM CHECKS, this is the starting point for utilizing the self-diagnostic system for determining computer-related problems. After performing necessary tests as described in the OBD system circuit check, if no codes are indicated and driveability problems still exist, see testing procedures in the TESTS W/O CODES article and SCAN TOOL usage in the TESTS W/CODES article.

  1. Turn ignition on with engine off. Observe Malfunction Indicator Light (MIL). If MIL illuminates, go to next step. If MIL does not illuminate, go to «MALFUNCTION INDICATOR LIGHT (MIL)»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__malfunction-indicator-light-mil) .
  2. Turn ignition off. Install Tech 1 scan tool and follow scan tool manufacturer's instructions to proceed with test. Turn ignition on. If scan tool displays PCM data, go to next step. If scan tool does not display PCM data, go to «DLC DIAGNOSIS OR NO SCAN TOOL DATA»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__dlc-diagnosis-or-no-scan-tool) .
  3. Attempt to start engine. If engine starts and runs, go to next step. If engine does not start, or starts and dies, go to «NO-START DIAGNOSIS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__no-start-diagnosis) .
  4. Using scan tool, observe DTC status LAST TST FAIL function. If any DTC is stored, save freeze frame and fail record information using CAPTURE INFO feature. If a DTC is indicated as last test failed, diagnose affected DTC. See the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article. If DTC is not indicated, go to next step.
  5. Using scan tool, display DTC fail records. If a DTC fail record is stored, save freeze frame and fail record information using scan tool CAPTURE INFO feature. If a fail record is stored, diagnose affected DTC. See the «TESTS W/CODES»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-tests-wcodes) article. If DTC is not indicated, go to next step.
  6. Compare scan tool engine data with actual control system data values. If value is within limits, system is okay. If value is not within limits, go to the «SYSTEM/COMPONENT TESTS»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-systemcomponent-tests) article.

MALFUNCTION INDICATOR LIGHT (MIL)

  1. Perform On-Board Diagnostic (OBD) System Check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . After performing OBD system check, go to next step.
  2. Attempt to start engine. If engine starts, go to next step. If engine does not start, go to step 6).
  3. Check instrument cluster ignition feed circuit fuse. See the «WIRING DIAGRAMS»(/pontiac/trans-sport/ii-1996-1999/remont/wiring-diagrams-engine-performance/#engine-performance-wiring-diagrams) article. If fuse is okay, go to next step. If fuse is faulty, go to step 15).
  4. Turn ignition on. Using test light connected to ground, probe ignition feed circuit at cluster connector. See the «WIRING DIAGRAMS»(/pontiac/trans-sport/ii-1996-1999/remont/wiring-diagrams-engine-performance/#engine-performance-wiring-diagrams) article. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
  5. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Using a fused jumper wire, connect MIL driver circuit at PCM to ground. See the «WIRING DIAGRAMS»(/pontiac/trans-sport/ii-1996-1999/remont/wiring-diagrams-engine-performance/#engine-performance-wiring-diagrams) article. If MIL illuminates, go to step 10). If MIL does not illuminate, go to step 11).
  6. Check PCM ignition feed and battery feed fuses. If both fuses are okay, go to step 7). If fuse(s) are faulty, go to step 14).
  7. Turn ignition off. Disconnect PCM harness connector. Using a test light connected to ground, probe ignition feed circuit at PCM harness connector terminal. See the «WIRING DIAGRAMS»(/pontiac/trans-sport/ii-1996-1999/remont/wiring-diagrams-engine-performance/#engine-performance-wiring-diagrams) article. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
  8. With test light connected to ground, probe battery feed circuit at PCM harness connector terminal. See the «WIRING DIAGRAMS»(/pontiac/trans-sport/ii-1996-1999/remont/wiring-diagrams-engine-performance/#engine-performance-wiring-diagrams) article. If test light illuminates, go to next step. If test light does not illuminate, go to step 13).
  9. Check for faulty PCM or poor PCM ground connection. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuit is okay, go to next step.
  10. Check for poor PCM connection. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If PCM connection is okay, go to step 16).
  11. Check for open in MIL driver circuit. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If circuit is okay, go to step 17).
  12. Repair open in ignition feed circuit to instrument cluster indicators. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  13. Locate and repair open in PCM battery feed circuit or PCM ignition feed circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  14. Locate and repair short to ground in PCM ignition feed circuit or PCM battery feed circuit. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  15. Locate and repair short to ground in feed circuit to instrument cluster indicators. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  16. Replace PCM. Perform PCM relearn procedures. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  17. Check for poor connection at MIL driver circuit in instrument cluster connector. Repair as necessary. After repairs, perform «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . If MIL driver circuit connections are okay, diagnose instrument panel. See the INSTRUMENT PANEL article in the ACCESSORIES/SAFETY EQUIPMENT section.

DLC DIAGNOSIS OR NO SCAN TOOL DATA

  1. Perform On-Board diagnostic (OBD) System check. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) . Turn ignition on. Using test light, probe between DLC battery feed terminal No. 16 (Orange wire) and ground terminal No. 4 or No. 5 (Black wire). If test light illuminates, go to step 3). If test light does not illuminate, go to next step.
  2. Using test light, probe between DLC battery feed terminal No. 16 (Orange wire) and ground. If test light illuminates, repair open circuit between DLC terminal No. 4 or No. 5 (Black wire) and ground. If test light does not illuminate, repair open or short to ground in DLC battery feed circuit. Recheck system. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  3. Turn ignition on. Using DVOM, check voltage between DLC connector terminal No. 2 (Purple wire) and ground. If voltage does not exist, go to next step. If voltage exists, go to step 6).
  4. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using DVOM, check voltage between DLC connector terminal No. 2 (Purple wire) and battery voltage. If voltage does not exist, go to next step. If voltage exists, repair short to ground between DLC connector terminal No. 2 and PCM connector C1 terminal No. 59 (Purple wire). Recheck system. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  5. Check for open circuit between DLC connector terminal No. 2 and PCM connector C1 terminal No. 59 (Purple wire). If no problem was found, go to step 7). If problem was found, repair as necessary and recheck system. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  6. Check for short to battery voltage between DLC connector terminal No. 2 and PCM connector C1 terminal No. 59 (Purple wire). If no problem was found, go to step 7). If problem was found, repair as necessary and recheck system. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .
  7. Replace PCM. Program PCM. Recheck system. See «ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK»(/pontiac/trans-sport/ii-1996-1999/remont/testing-diagnostics/#engine-control-system-basic-engine-testing__on-board-diagnostic-obd-system-check) .

SUMMARY

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, no trouble codes (or only intermittent ones) were found while performing ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK and driveability problems exist, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.

More articles — Engine Performance