With help from ALLDATA, TechShop breaks down an unusual problem on a 2005 GMC Sierra 2500 4WD truck with the 6.6 liter diesel engine.
The truck would crank initially, but stop cranking before the engine would start. Occasionally it would start, but if so it would immediately stall.
To diagnose this case, the technician verified the symptom, then checked for trouble codes, and there were none.
So the next step was to verify fuel pressure, which was found to be ok.
The technician decided to consult with ALLDATA Tech-Assist, and was advised to check the cranking speed, which was indicated on the scan tool be 900 RPM.
It turns out that the indicated cranking speed was too high, and when the powertrain control module sees an RPM that is fast enough to indicate that the engine should be running, it shuts the starter off, which explained the problem, but then the question was what caused the cranking speed to be indicated higher than the speed the starter could normally crank the engine?
Tech-Assist recommended that the Crankshaft Position Sensor signal be checked with an oscilloscope, and upon performing this test, the signal was full of glitches.
Further inspection found that the crankshaft position sensor terminals were loose in the connector. The connector was replaced and the problem was fixed.