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Tim 12/6/2019

2008 Chevrolet Silverado 1500 LTZ 8 Cyl 5.30L


Open loop fault both banks

Truck is in open loop fault on both banks while idling. On cold starts and after warming up. Goes into closed loop while diving but back to open loop fault when I stop. Only code is a misfire in cylinder 8. O2 sensor and fuel trims read normal while in closed loop and become stagnant when it goes into open loop fault. I have read that a larger cam will cause this, but everything is factory. No changes to motor. Temp sensor and maf sensor seem to be working under normal conditions. Please any help.

1 Answer


Jimm 12/7/2019

Open Loop - Fault is when both upstream oxygen or A/F sensors on a two bank vehicle have a fault. This could be caused by two bad upstream O2 sensors or both banks can be extremely rich or extremely lean.

Check for engine vacuum leaks, in particular the upper and lower intake manifold gaskets.

Intake manifold gasket set = MAHLE part #MIS16340 - or it's equivalent
(Contains Intake and Valve Cover Gaskets Plus All Miscellaneous Gaskets And Seals Needed for Intake Installation)


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