Engine Cranks But Does Not Run
Engine Cranks But Does Not Run
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
Circuit/System Description
This Engine Cranks but Does Not Run diagnostic is an organized approach to identify a condition which causes the engine to crank but does not continue to run. This diagnostic directs the service technician to the appropriate system diagnosis. This diagnostic assumes the vehicle system voltage levels are adequate for starter motor operation. Refer to Battery Inspection/Test (Battery Inspection/Test) and Engine Cranks Slowly (Engine Cranks Slowly). The fuel level supply must be adequate, and the fuel quality must be able to sustain the combustion process.
Diagnostic Aids
* The Immobilizer system is not designed to have the key FOB folded 90 degrees when attempting to start the engine. This may cause an intermittent no start condition. If you receive a customer complaint of an intermittent no start condition, verify that the customer is not folding the key while attempting to start the engine. The fob must be parallel to the key to function properly.
* Insufficient fuel can cause a no start condition. Thoroughly inspect the fuel delivery system for sufficient fuel volume to the fuel injectors. Inspect the fuel supply components for partial blockage or restrictions.
* Fuel injectors with partially blocked and restricted nozzles, or a malfunctioning solenoid, can cause a no start condition. Refer to Fuel Injector Diagnosis (Testing and Inspection).
* There may be fuel spray at the fuel injectors and the indicated fuel pressure may be correct, yet there may not be enough fuel to start the engine. If the fuel injectors and the injector circuit are OK, and fuel spray is detected, the fuel injector ON time may be inadequate. If the engine control module (ECM) receives incorrect inputs from the various information sensors, the fuel delivered by the fuel injectors may be inadequate to start the engine. Check all the engine data parameters with a scan tool and compare the values indicated with the expected values or the values from a known good vehicle.
* Observe the Engine Speed parameter while cranking the engine. The scan tool should indicate a steady 200-300 RPM while cranking. If erratic values, such as sudden spikes in the engine speed are displayed, the engine reference signal is not stable enough for the engine to start and run properly.
* Inspect the engine for good secure electrical grounds.
* If the engine almost starts and then stalls, check for an open in the ground circuits of the crankshaft position sensor and the camshaft position sensor.
* Water or foreign material in the fuel can cause a no start or engine will not stay running condition. During freezing weather water can freeze inside the fuel system. The engine may start after 30 minutes in a heated repair shop. The malfunction may not recur until parked overnight in freezing temperatures. Extreme weather conditions can cause contaminated fuel to prevent the vehicle from starting.
* A vehicle that starts and runs after being brought to the repair shop for a no start condition, may have an ignition system that is susceptible to moisture. Spray water on the ignition system components and the wiring in order to check for an engine starting or will not stay running concern.
* Use the J 35616 - Test Kit for any test that requires probing the underhood fuse block terminals, component wire harness terminals, or the ECM wire harness terminals.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Special Tools
* J 34730-1A - Fuel Pressure Gauge
* J 35616 - GM-Approved Terminal Test Kit
* J 35616-A/BT-8637 - Connector Test Adapter Kit
* J 43244 - Relay Puller Pliers
Circuit/System Verification
Note: This diagnostic assumes the following:
* The battery is completely charged. Refer to Battery Inspection/Test (Battery Inspection/Test).
* The engine cranking speed is acceptable. Refer to Engine Cranks Slowly (Engine Cranks Slowly).
* There is adequate fuel in the fuel tank.
Attempt to start the engine. The engine should start and continue to run. An engine that starts and stalls is considered to not run.
If the vehicle passes the Circuit/System Verification test, refer to Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections).
Circuit/System Testing
1. Crank the engine while observing the scan tool Vehicle DTC Information.
• If any of the following DTCs are set, diagnose these DTCs first: DTC P0117, P0118, P0122, P0123, P0201-P0208, P0222, P0223, P0335, P0336, P0351-P0358, P0562, P0563, P0601-P0604, P0607, P062F, P0633, P0685, P0690, P1631, P1682, or P2610. Refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).
2. With the ignition ON and the engine OFF, test the fuses that are supplied ignition 1 voltage by the powertrain relay. The test lamp should illuminate ON for each test point of the fuses.
• If the test lamp does not illuminate ON for at least one test point of each fuse, refer to DTC P0685 or P0690 (P0685).
3. Crank the engine while observing the scan tool engine speed parameter.
• If engine RPM is not indicated, refer to DTC P0335 (P0335).
4. Disconnect the B75B mass airflow (MAF) sensor. Attempt to start the engine. The ECM will ignore MAF sensor input, default to calculated airflow, and the engine should start and run if the MAF sensor is faulted.
• If the engine starts and runs, and the MAF sensor circuits test OK, replace the B75B MAF sensor.
5. Install a spark plug tester onto one T8 ignition module/coil assembly on each bank of the engine.
Note: An erratic or weak spark is considered a no spark condition.
6. Crank the engine while observing both spark plug testers. Both spark plug testers should spark.
• If spark is not observed, is inconsistent, or weak on either spark plug tester, refer to Electronic Ignition System Diagnosis (Electronic Ignition System Diagnosis).
7. With the ignition ON and the engine OFF, command the fuel pump ON and OFF with the scan tool. The fuel pump should energize when commanded ON, and de-energize when commanded OFF.
• If the fuel pump does not turn ON and OFF, refer to Fuel System Diagnosis (Fuel System Diagnosis).
8. Turn OFF the ignition.
9. Install the J 34730-1A - Gauge Fuel Pressure Gauge. Refer to Fuel Pressure Gauge Installation and Removal (Fuel Pressure Gauge Installation and Removal). With the ignition ON and the engine OFF, command the fuel pump ON several times with the scan tool. Refer to Fuel System Diagnosis (Fuel System Diagnosis) for the fuel pressure specification.
10. Verify the following conditions do not exist:
* Restricted air filter element or air intake system
* Spark plugs for being gas or coolant fouled-Refer to Spark Plug Inspection (Testing and Inspection)
* A skewed manifold absolute pressure (MAP) sensor-Refer to DTC P0106 (P0106).
* A skewed engine coolant temperature (ECT) sensor-Refer to DTC P0116 (P0116).
* Exhaust system restricted-Refer to Restricted Exhaust (Restricted Exhaust).
* Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Alcohol/Contaminants-in-Fuel Diagnosis).
* Engine mechanical condition, for example, worn timing chain, sprocket gears, low compression, etc.-Refer to Symptoms - Engine Mechanical (Symptoms - Engine Mechanical) and Timing Chain, Crankshaft Sprocket, Camshaft Position Actuator, and Solenoid Valve Replacement.
• If any of the above conditions exist, repair as necessary.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.