Diagnostic Instructions
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
and
Engine Cranks Slowly
. The fuel level supply must be adequate,
and the fuel quality must be able to sustain the combustion process.
Diagnostic Aids
• | When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect both mating electrical terminals for corrosion and terminal tightness. |
• | Use the
J 35616
Connector Test Adapter 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
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Special Tools Required
J 34730-1A
Fuel Pressure Gage
Circuit/System Verification
Attempt to start the engine. The engine should start and run.
Circuit/System Testing
- Crank the engine for 15 seconds.
- Observe the vehicle DTC information with a scan tool.
- 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.
- Crank the engine for 15 seconds. Observe the engine speed parameter with a scan tool.
- Install a spark plug tester onto one ignition module/coil assembly, on each bank of the engine.
- Observe both spark plug testers.
Important: An erratic or weak spark is considered a no spark condition.
- Crank the engine for 15 seconds. The ignition coil secondary voltage should be observed across the gap of both spark plug testers.
- 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.
- Turn OFF the ignition.
- Install the
J 34730-1A
Fuel Pressure Gage. With the ignition ON and the engine OFF, command the fuel pump ON several times with the scan tool. Refer to
Fuel System Diagnosis
for the fuel pressure specification.
- Inspect for the following conditions:
• | Compare the actual engine coolant temperature to the ECT parameter |
• | Filter and air intake system for restrictions and obstructions |
• | Engine mechanical conditions, such as worn timing chain, sprocket gears, low compression, etc--Refer to
Engine Compression Test
. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.