Engine Cranks But Does Not Run (LF1)
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Engine Cranks But Does Not Run (LF1)
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Circuit/System Description
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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.
Inspect for any of the following conditions:
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When attempting to start the engine, the mechanical portion of the vehicle key must be locked in the fully extended position with the fob parallel to the key. If the key is partially retracted or folded over when starting may interrupt transponder authentication. This may result in an intermittent no-start condition. In such instances, DTC B3055 may also be set. If an intermittent no-start complaint is received, it may be necessary to discuss with the customer their starting habits. Verify they are locking the key in the fully extended position, key ring parallel to the key, before starting.
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The engine control module (ECM) uses the camshaft position (CMP) sensors to determine engine speed and position when there is a crankshaft position (CKP) sensor condition.
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The engine will operate with a CKP sensor condition only if the ECM has stored the learned reference position of the camshafts in memory. With a CKP 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 CMP sensors.
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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).
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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.
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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.
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Inspect the engine for good secure electrical grounds.
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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.
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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.
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Schematic Reference
Engine Controls Schematics (3.0L (LF1))
Engine Controls Schematics (2.8L (LAU))
Connector End View Reference
Component Connector End Views
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
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Circuit/System Verification
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1.
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Verify there is adequate fuel in the fuel tank.
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2.
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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.
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Engine cranking, observe the Engine Speed parameter with a scan tool. The reading should show engine speed greater than 175 RPM.
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6.
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If engine speed reading is 0 RPM, refer to
DTC P0335 (LF1, LFW)
for crankshaft position sensor diagnosis.
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7.
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Ignition ON, observe the ECM, fuel pump control module, and theft deterrent module DTC information with a scan tool. No DTCs should be set.
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9.
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Disconnect the B75B mass airflow (MAF) sensor. Attempt to start the engine. The ECM will ignore MAF sensor input and start based on calculated airflow. The engine should start and run if the MAF sensor is faulted.
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If the engine starts and runs, and the MAF sensor circuits test OK, replace the B75B MAF sensor.
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Ignition OFF, inspect the engine air filter, intake duct, and B75B MAF sensor. The air way should be clear.
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12.
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If the intake duct is blocked or collapsed, or the filter is restricted or water saturated, repair or replace as necessary.
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13.
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If the MAF sensor is damaged or contains water, replace it.
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Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. The reading should be less than 80%.
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Ignition ON, observe the BARO parameter with a scan tool. Determine your altitude and compare the BARO reading to the
Altitude Versus Barometric Pressure
table. The reading should be within the range specified.
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If the reading is not within the specified range in the table, and the barometric pressure sensor circuits test OK, replace the B17 barometric pressure sensor.
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Ignition OFF, remove and inspect the engine spark plugs. They should be dry.
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21.
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If the spark plugs are fuel fouled, replace the spark plugs.
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23.
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If the fuel is contaminated with water, dirt, or other debris, replace the fuel filter and refer to
Fuel System Cleaning
.
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24.
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If the fuel is not the correct type, drain the fuel system and the fuel tank. Then fill up with correct fuel.
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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).
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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.
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28.
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Test the engine compression. Refer to
Engine Compression Test
. The compression should be within specification.
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29.
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If engine compression is not within specification, repair the engine as necessary.
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30.
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Inspect the exhaust system. The exhaust system should be free of restrictions. Refer to
Restricted Exhaust
.
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31.
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If a restriction or blockage is found, repair the exhaust system as necessary.
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33.
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If a condition is found, repair the engine as necessary.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
