Tech Tips (by ALLDATA): GMC Sierra starter stops cranking with key in start position
TECH TIPS (courtesy of ALLDATA)
Problem: The truck was towed to the shop because, while holding the key in the Start position, the starter would begin cranking the engine over, then stop cranking before the engine started.
Details: When the technician called Tech-Assist, the consultant asked him to check the fuel rail pressure while cranking (NOTE: Specification is 6000 psi). The fuel pressure was correct.
Next, he asked the technician to check the cranking speed. The technician connected a scan tool to check RPM. The cranking speed was 900 RPM. That was way too high. The consultant explained to the technician that Powertrain Control Module shuts the starter off when it sees an RPM that is fast enough to indicate the engine should be running. Because the cranking RPM read high on the scan tool, and the engine didn’t seem to be cranking that fast, the consultant asked the technician to scope crankshaft position (CKP) sensor signal.
When he scoped CKP, he found the signal was full of glitches. Upon further inspection, the technician found the CKP terminals were loose in the connector.
Confirmed Repair: The technician replaced the CKP connector and made sure that the two connector halves locked together tightly. After that repair, the engine cranked over and started normally. Fixed!