Engine Control System - Trouble Shooting - No Codes - 4.2L: Other Chevrolet TrailBlazer I

Possible Causes & Corrections

Check the following items

1. Low engine coolant level.
2. Correct coolant mixture.
3. Proper tension on the drive belts.
4. Restricted air flow through the radiator or restricted coolant flow.
5. Faulty thermostat.
6. Inspect for an Engine Coolant Temperature (ECT) sensor that has a shift in value. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the problem.
8. If system is lean, the long term fuel trim will be more than 150 on scan tool.
9. Test fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
10. Inspect for a poor fuel quality and a proper octane rating.
11. If fuel trim readings are normal and there are no engine mechanical concerns, fill fuel tank with a known-good fuel and re-evaluate vehicle performance.
12. Inspect spark plugs for proper heat range and gap.
13. Inspect Knock Sensor (KS) system operation.
14. Inspect ignition timing.
15. Inspect for carbon build up. Remove carbon with a top engine cleaner.
16. Test the combustion chamber pressure by performing a compression test. See CYLINDER COMPRESSION PRESSURE under «MECHANICAL INSPECTION»(ref-152692-S27774824292003021900000) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
17. Test the Torque Converter Clutch (TCC) operation. TCC applying too soon can cause engine to spark knock. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
18. Search for Service Bulletins for calibration updates.

Check the following items

1. Inspect ignition system.
2. Inspect engine for engine compression. See CYLINDER COMPRESSION PRESSURE under «MECHANICAL INSPECTION»(ref-152692-S27774824292003021900000) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. A low compression can be caused by improper valve timing, faulty manifold gaskets, or sticking/leaking valves.
3. Inspect intake and exhaust system for fresh air entering the exhaust upstream of the catalytic converter or restrictions.
4. Inspect fuel system. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Perform the fuel injector balance test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

Check the following items

1. Test for a cylinder misfire. Start engine and allow to stabilize. DO NOT perform this test for more than 2 minutes to prevent damaging catalytic converter. Perform Cylinder Power Balance Test with a scan tool. If there is an RPM drop on all cylinders, equal to within 50 RPM, refer to «ROUGH, UNSTABLE OR INCORRECT IDLE AND STALLING»(ref-152936-S09724193992003030500000) . If there is no spark, refer to «NO-START- ENGINE CRANKS OKAY»(ref-152692-S35433692032003021900000) under NO-START DIAGNOSIS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If there is spark, remove spark plugs in affected cylinders and inspect for insulation cracks, wear, improper gap, burned electrodes, or heavy deposits. Check ignition system for moisture, dust, cracks, burns, etc.
2. Perform Fuel Injector Balance Test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Perform a cylinder compression check. See CYLINDER COMPRESSION PRESSURE under «MECHANICAL INSPECTION»(ref-152692-S27774824292003021900000) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Inspect the engine for improper valve timing, worn rocker arms, worn camshaft lobes, broken or weak valve springs, and intake and exhaust manifold passages for casting flash.
5. Test fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
6. Inspect for water contamination in fuel.
7. Perform the fuel injector coil test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
8. Perform the fuel injector balance test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

Check for the following

1. Inspect the Evaporative Emission (EVAP) system and fuel tank venting.
2. Inspect fuel injectors for leakage. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
3. Perform a fuel system diagnosis. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

Check the following items

1. Search for bulletins.
2. Ensure vehicle operator is using the correct starting procedure.
3. Monitor Engine Coolant Temperature (ECT) sensor with scan tool. Compare engine coolant temperature with the ambient air temperature on a cold engine. If coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sensor circuit.
4. Inspect for a restricted exhaust.
5. Inspect the fuel pump relay for proper operation. The fuel pump should operate for the first 2 seconds after turning ignition on. Refer to Fuel Pump Electrical Circuit Diagnosis under «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
6. Test fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Inspect for water contamination in fuel.
8. Perform fuel injector coil test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
9. Perform fuel injector balance test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
10. Inspect fuel pump check valve. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
11. Inspect the spark plugs for wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
12. Inspect for loose ignition coil connections
13. Inspect for loose ignition control module connections.
14. Inspect for a faulty control module or ignition system grounds.
15. Improper valve timing.
16. Low compression.
17. Worn rocker arms.
18. Broken or weak valve springs.
19. Worn camshaft lobes.
20. Proper Cam Phaser operation.
21. Inspect for a restricted exhaust.

Check for the following items

1. Test fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
2. Inspect Throttle Position (TP) sensor for binding or sticking. Voltage should increase at a steady rate as the throttle moves toward Wide Open Throttle (WOT) position.
3. Inspect Manifold Absolute Pressure (MAP) sensor response and accuracy. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Test for water contamination in fuel.
5. Test canister purge system for proper operation.
6. Perform fuel injector coil test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
7. Perform fuel injector balance test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
8. Test for low fuel pressure after a cold start or during a moderate or full throttle acceleration.
9. Inspect for fouled spark plugs.
10. Inspect for proper ignition system performance.
11. Search for Service Bulletins for calibration updates.
12. Test generator output voltage.
13. Inspect for a restricted exhaust.

Check the following items

1. Compare customer vehicle with a similar unit. Verify the customer's concern.
2. Remove air filter and check for dirt or a restriction.
3. Inspect transmission shift pattern and downshift operation.
4. Inspect for a restricted fuel filter, contaminated fuel, or improper fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
5. Perform the fuel injector balance test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
6. Inspect exhaust system for a possible restriction.
7. Inspect exhaust system for damaged or collapsed pipes. Inspect the muffler for heat distress or a possible internal failure.
8. Inspect control module grounds for being clean, tight, and in their proper location.
9. Inspect Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
10. Inspect A/C operation.
11. Test generator output voltage.
12. Monitor Knock Sensor (KS) system for retarded timing.
13. Engine compression. See CYLINDER COMPRESSION PRESSURE under «MECHANICAL INSPECTION»(ref-152692-S27774824292003021900000) under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. Low compressions can be caused by faulty valve timing or improper or worn camshaft.
14. Camshaft Phaser for proper operation.

Check the following items

1. Inspect the air cleaner element or filter, for dirt or being plugged.
2. Visually and physically check the vacuum hoses for splits, kinks, and proper connections as shown on the underhood Vehicle Emission Control Information label.
3. Discuss the driving habits with the owner. Check if A/C is ON full time or if defroster mode is ON? Check tires for proper inflation. Check that wheel and tires are the correct size. Check for excessively heavy loads being carried or an aggressive driving habits
4. Suggest to owner to fill the fuel tank and to inspect the fuel economy.
5. Suggest to driver to refer to Important Facts on Fuel Economy in the owner manual.
6. Inspect fuel type, quality and alcohol content.
7. Test fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
8. Inspect spark plugs. Remove and check for wet plugs, cracks, wear, improper gap, burned electrodes or heavy deposits.
9. Inspect for an open Ignition Control (IC) circuit.
10. Inspect Knock Sensor (KS) system operation.
11. Inspect engine coolant level.
12. Inspect engine thermostat for being open or for wrong heat range.
13. Inspect transmission shift pattern.
14. Inspect Torque Converter Clutch (TCC) operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
15. Inspect for proper calibration of the speedometer.
16. Inspect for dragging brakes.

Possible Cause & Correction

Check the following items

1. Check valve stuck closed.
2. Fill limiter vent valve stuck closed.
3. Restricted Evaporative Emission (EVAP) canister.
4. EVAP vent valve stuck closed.
5. Restricted vapor lines.
6. High Reid Vapor Pressure (RVP) or high fuel temperature.
7. Fuel filler hose is pinched or kinked.
8. Ignition is on.

Check the following items

1. Pressure relief valve in fill limiter vent valve stuck open.
2. Pressure relief valve in fill limiter vent valve is leaking.
3. Fill limiter vent valve stuck open.
4. Fill limiter vent valve is leaking.

Check the following items

1. Fill limiter vent valve stuck closed.
2. EVAP canister restricted.
3. EVAP vent valve stuck closed or restricted vapor lines.
4. Restricted vapor lines.
5. High Reid Vapor Pressure (RVP) or high fuel temperature.
6. Ignition is on.

Check the following items

1. Check valve stuck open.
2. Check valve stuck closed or check valve is leaking.
3. Check valve leaking.
4. High Reid Vapor Pressure (RVP) or high fuel temperature.

Check the following items

1. Fill limiter vent valve stuck open.
2. Fill limiter vent valve leaking.

Check the following items

1. Pressure relief valve in fill limiter vent valve stuck open or leaking.
2. Fuel filler hose loose or torn.
3. Fill limiter vent valve stuck open.

Check the following items

1. Pressure relief valve in fuel limiter vent valve stuck open or leaking.
2. Saturated EVAP canister.

Check the following items

1. Inspect the Heated Oxygen Sensor (HO2S). Check for silicone contamination from fuel or improperly used sealant. The sensor will have a White powdery coating. The sensor will result in a high but false signal voltage or rich exhaust indication. The control module will reduce the amount of fuel delivered to the engine causing a severe driveability condition.
2. Inspect Engine Coolant Temperature (ECT) sensor using scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. If coolant temperature reading is more than 5 degrees more than or less than the ambient air temperature on a cold engine, test for a high resistance in the coolant sensor circuit or the sensor itself. Inspect the manifold absolute pressure (MAP) sensor response and accuracy.
3. Test fuel pressure. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
4. Inspect to determine if a rich or lean system causes the condition. Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the condition. Using scan tool, observe fuel trim conditions. A lean condition will indicate a long term fuel trim of more than 150. A rich condition will indicate a long term fuel trim of less than 115.
5. Perform fuel injector balance test. Refer to «FUEL SYSTEMS»(ref-153168-S03975234652003032100000) in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
6. Test fuel injector driver circuit. Disconnect injector harness connector. Connect an injector test light between the terminals of each injector connector and observe test light while cranking. If test light fails to blink at any connector, injector drive circuit harness connector or terminal is faulty.
7. Perform fuel injector coil test. Refer to «SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-153168) article.
8. Inspect Evaporative Emission (EVAP) control system.
9. Inspect the overall ignition system.
10. Inspect spark plugs. Check for wet plugs, cracks, wear, improper gap, burned electrodes, blistered insulators or heavy deposits.
11. Inspect for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low Idle Air Control (IAC) counts.
12. Inspect control module grounds for being clean, tight and in their proper locations.
13. Observe scan tool to determine if the control module is receiving an A/C signal. If a condition exists with the A/C ON, inspect the A/C system operation.
14. Inspect battery cables and ground straps for being clean and secure.
15. Inspect the crankcase ventilation valve for proper operation by placing a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace PCV.
16. Broken motor mounts.
17. Improper valve timing.
18. Low compression.
19. Worn rocker arms.
20. Broken or weak valve springs or worn camshaft lobes.

Check for the following items

1. Ensure driver understands the torque converter clutch operation and A/C compressor operation.
2. Ensure that the transmission fluid is at the proper level.
3. Display scan tool parameters for the various engine controls sensors. Inspect for any abnormal readings.
4. Inspect for a rich or lean symptom that causes the condition. Drive vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the condition.
5. Lean condition. The long term fuel trim will be more than 150 displayed on scan tool.
6. Rich condition. The long term fuel trim will be less than 115 displayed on scan tool.
7. Test fuel pressure while the condition exists. Refer to «FUEL SYSTEMS»(ref-152692-S00601502122003021900000) in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
8. Inspect the in-line fuel filter for a restrictions.
9. Inspect spark plugs. Remove plugs and inspect for wetness, cracks, wear, improper gap, burned electrodes or heavy deposits.
10. Inspect the control module grounds for being clean, tight, and in their proper locations.
11. Test the generator output voltage.
12. Inspect vacuum hoses for kinks or leaks.
13. Inspect TCC operation. See appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS.
14. Inspect exhaust system for a possible restriction.

RESTRICTED EXHAUST

For dual exhaust systems a quick check of exhaust flow will help determine which side of the exhaust system is restricted. The side that has less exhaust flow is the side that will be suspect, and diagnosis should begin there. To diagnose exhaust system, refer to EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

INTERMITTENTS

Note. Intermittent is a DTC or symptom, with a condition that cannot be duplicated.

PRELIMINARY

Perform the Diagnostic System Check-Engine Controls before starting. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

CONTROL MODULE POWER & GROUNDS, & COMPONENT POWER & GROUNDS

Poor power or ground connections can cause widely varying symptoms.

1. Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test light or a Digital Volt-Ohmmeter (DVOM) may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. See POWER DISTRIBUTION in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.
2. Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. See GROUND DISTRIBUTION in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

TEMPERATURE SENSITIVITY

1. An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot.
2. The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records. Scan tool snapshot. Vehicle data recorder.
3. If the intermittent is related to heat, review the following data: High ambient temperatures. Underhood or engine generated heat. Circuit generated heat due to a poor connection, or high electrical load. Higher than normal load conditions, such as towing.
4. If the intermittent is related to cold, review the following data: Low ambient temperatures. In extremely low temperatures, ice may form in a connection or component. Test for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up.
5. Information from the customer may help to determine if the trouble follows a pattern that is temperature related.

INCORRECT PCM PROGRAMMING

1. There are only a few situations when reprogramming a PCM is appropriate, such as the following: A new service PCM is installed. A PCM from another vehicle is installed. Revised software or calibration files have been released for this vehicle.
2. Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software or calibration. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) under PROGRAMMING in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

DUPLICATING FAILURE CONDITIONS

1. If none of the previous tests are successful, attempt to duplicate or capture the failure conditions.
2. Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records data. Clear DTCs using scan tool. Turn ignition off and wait 15 seconds. Operate vehicle under the same conditions that were noted in Freeze Frame/Failure Records data, as closely as possible. The vehicle must also be operating within the Conditions for Running DTC. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
3. An alternate method is to drive vehicle with DVOM connected to a suspected circuit. An abnormal reading on the DVOM when problem occurs, may help you locate the problem.

VEHICLE DATA RECORDER

The Vehicle Data Recorder (J-42598) is connected to the Data Link Connector (DLC) and sent with customer. The vehicle data recorder captures data for later retrieval and analysis by the technician. Refer to vehicle data recorder user instructions for more information.