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 procedure is an organized approach to identify a condition which causes the engine to crank but not start. This diagnostic procedure directs the technician to the appropriate system diagnosis.

Diagnostic Aids

Inspect for any of the following conditions:

* The engine control module (ECM) uses the camshaft position sensors to determine engine speed and position when there is a crankshaft position sensor condition.
* The engine will operate with a crankshaft position sensor condition only if the ECM has stored the learned reference position of the camshafts in memory. With a crankshaft position sensor condition in the signal circuit, the engine will go into a limp home mode after a hard restart. The ECM then calculates engine speed from one of the camshaft position sensors.
* The fuel pump control module controls and monitors the operation of the in-tank fuel pump. If the fuel pump control module detects a fault, a DTC sets in the fuel pump control module. The fuel pump control module will then send a serial data message to the engine control module (ECM) requesting the illumination of the malfunction indicator lamp (MIL).
* 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 Solenoid Coil Test Fuel Injector Solenoid Coil Test.
* 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.
* Inspect the engine for good secure electrical grounds.
* 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 min 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.

Reference Information
Schematic Reference

Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

* Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis
* Fuel System Description Fuel System Description
* Immobilizer Description and Operation Immobilizer

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

Scan Tool Reference

Control Module References Programming and Relearningfor scan tool information

Circuit/System Verification

1. Verify there is adequate fuel in the fuel tank.
2. Ignition ON, test the fuses that are supplied voltage by the powertrain relay. The test lamp should illuminate for each test point of the fuses.

• If the test lamp does not illuminate for at least one test point of each fuse, refer to DTC P0685, P0689, or P0690 P0685 for powertrain relay system diagnosis.

3. Engine cranking, observe the Engine Speed parameter with a scan tool. The reading should show engine speed greater than 175 RPM.

• If the cranking speed is slow, refer to Engine Cranks Slowly Engine Cranks Slowly.
• If engine speed reading is 0 RPM, refer to DTC P0335 P0335 for crankshaft position sensor diagnosis.

4. Ignition ON, observe the ECM, fuel pump control module, and theft deterrent module DTC information with a scan tool. No DTCs should be set.

• If there are any DTCs set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle for diagnosis.

5. 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.

6. Ignition OFF, inspect the engine air filter, intake duct, and B75B MAF sensor. The air way should be clear.

• If the intake duct is blocked or collapsed, or the filter is restricted or water saturated, repair or replace as necessary.
• If the MAF sensor is damaged or contains water, replace it.

7. Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. The reading should be less than 80%.

• If the reading is greater than 80%, inspect the Q38 throttle body bore for excessive carbon deposits and clean the throttle body. Refer to Throttle Body Cleaning Procedures.

8. Perform the Electronic Ignition System Diagnosis Electronic Ignition System Diagnosis to verify the ignition system provides spark to the cylinders.
9. Ignition OFF, remove and inspect the engine spark plugs. They should be dry.

• If the spark plugs are coolant fouled, refer to Coolant in Combustion Chamber Coolant in Combustion Chamber.
• If the spark plugs are fuel fouled, replace the spark plugs.

10. Collect a fuel sample from the fuel tank. The sample should be bright and clear, free of water, dirt, or other debris. Also, verify the fuel is the correct type for this engine. Refer to Alcohol/Contaminants-in-Fuel Diagnosis Alcohol/Contaminants-in-Fuel Diagnosis. For vehicles that are E85 compatible, refer to Fuel Composition Diagnosis Fuel Composition Diagnosis.

• If the fuel is contaminated with water, dirt, or other debris, replace the fuel filter and refer to Fuel System Cleaning Service and Repair.
• If the fuel is not the correct type, drain the fuel system and the fuel tank and replace with the correct type.

11. Perform the Fuel System Diagnosis Fuel System Diagnosis to verify proper fuel pump operation and fuel pressure.
12. Ignition ON, observe the ECT Sensor parameter with a scan tool. Compare the parameter reading to the actual engine coolant temperature. The readings should be within ±3°C (±5°F).

• If the temperature readings are not within the ±3°C (±5°F) of each other and the ECT sensor circuits test OK, replace the B34 ECT sensor.

13. Test the engine compression. Refer to Engine Compression Test Testing and Inspection. The compression should be within specification.

• If engine compression is not within specification, repair the engine as necessary.

14. Inspect the exhaust system. The exhaust system should be free of restrictions. Refer to Restricted Exhaust Restricted Exhaust.

• If a restriction or blockage is found, repair the exhaust system as necessary.

15. Ignition OFF, inspect the timing chain and sprockets. They should be properly aligned, free of damage, with minimal wear. Refer to Camshaft Timing Chain and Sprocket Replacement Service and Repair and Camshaft Timing Chain and Sprocket Cleaning and Inspection 14. Camshaft Timing Chain and Sprocket Cleaning and Inspection.

• If a condition is found, repair the engine as necessary.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Air Cleaner Element Replacement (NU6) Air Cleaner Element Replacement (NU6)Air Cleaner Element Replacement (NT7) Air Cleaner Element Replacement (NT7)
* Air Cleaner Inlet Duct Replacement Air Cleaner Inlet Duct Replacement
* Air Cleaner Outlet Duct Replacement Air Cleaner Outlet Duct Replacement
* Spark Plug Replacement Service and Repair
* Mass Airflow Sensor with Intake Air Temperature Sensor Replacement (NU6) Mass Airflow Sensor with Intake Air Temperature Sensor Replacement (NU6)Mass Airflow Sensor with Intake Air Temperature Sensor Replacement (NT7) Mass Airflow Sensor with Intake Air Temperature Sensor Replacement (NT7)
* Engine Coolant Temperature Sensor Replacement Service and Repair