Sometimes you need to go back to an old-fashioned method to diagnose a problem and find the cause. SureTrack community member Peirs13 had a GMC Sierra pickup in their shop that ran great but would intermittently go into limp in mode and set a bunch of codes. They did all the normal testing for the situation but still didn’t find the cause. They posed the question to the community, and with the help of fellow community member ericsautomotive, and others, they were able to resolve the issue quickly.
The following Community Fix summarizes the interaction between members of the community that led to the solution.
Vehicle
2003 GMC Sierra 1500 HD 6.0L
Title
Goes into limp in mode, replaced intake manifold.
Complaint
Customer complains that truck will intermittently go into limp in mode.
Diagnostic Steps Performed/Parts Replaced
Scanned for codes and found P0106, P0171, P0174, P0300 and P1516. Truck runs great, intermittently goes into limp mode. Throttle body, MAF, MAP were all recently replaced. Truck was bought at auction. Replaced plugs and wires and intake gaskets within past month. Checked all power and grounds, tested all circuits; throttle body, MAP, and MAF to PCM, and TAC module. Went through all pinpoint tests for codes and get referred to diagnostic aids section. Smoke tested and found no leaks. Freeze frame data shows faults set on cold start, intermittently goes into limp mode at operating temperature. MAP, Baro, MAF data reads normally. Will crank right up after limp mode and return to normal.
Cause
Found pinhole size crack underneath intake manifold towards the rear, could barely see it. Couldn’t see smoke coming out during smoke test. Found by spraying brake clean around engine and watching idle speed.
Correction
Replaced intake manifold. Cleared codes and road tested vehicle. Codes did not return and vehicle operates as it should.