Systems and methods for intake oxygen sensor diagnostics

1. A method comprising:

injecting fuel into one or more cylinders of an engine of a vehicle without combustion, and routing un-combusted hydrocarbons from the one or more cylinders to a crankcase of the engine, the crankcase included in a crankcase ventilation system, and then to an intake manifold of the engine, in order to diagnose whether a first intake air oxygen sensor positioned in the intake manifold is functioning as opposed to malfunctioning due to degradation; and

subsequent to routing un-combusted hydrocarbons to the intake manifold of the engine, routing the un-combusted hydrocarbons to a position upstream of the intake manifold of the engine, to diagnose whether a second intake air oxygen sensor positioned in an intake passage of the engine is functioning.

2. The method of claim 1 , wherein routing uncombusted hydrocarbons further comprises rotating the engine in a forward direction via a motor configured to rotate the engine, without providing spark to the one or more cylinders, and wherein the forward direction comprises a same direction of rotation as when the engine is operating to combust air and fuel.

3. The method of claim 1 , further comprising commanding fully open a throttle configured to control an amount of air inducted to the engine during conditions of engine operation.

4. The method of claim 3 , wherein commanding fully open the throttle controls pressure in the intake manifold such that a positive crankcase valve positioned in a conduit coupling the crankcase to the intake manifold occupies a least-restrictive position.

5. The method of claim 1 , wherein routing uncombusted hydrocarbons further comprises sealing the one or more cylinders of the engine.

6. The method of claim 5 , wherein sealing the one or more cylinders of the engine includes commanding intake and exhaust valves coupled to each of the one or more cylinders of the engine to fully closed positions; and

wherein the engine comprises a variable displacement engine, and wherein commanding the intake and exhaust valves coupled to each of the one or more cylinders to the fully closed positions involves actuating a first variable displacement engine actuator and actuating a second variable displacement engine actuator.

7. The method of claim 1 , wherein routing uncombusted hydrocarbons is in further response to a temperature of the engine below a threshold engine temperature, and wherein one or more piston rings coupled to pistons of the one or more cylinders of the engine are inefficient at sealing the one or more cylinders from the crankcase.

8. The method of claim 1 , further comprising:

indicating the first intake air oxygen sensor is functioning provided the first intake air oxygen sensor responds to the routed un-combusted hydrocarbons with a first output above a first threshold; and

indicating the second intake air oxygen sensor is functioning provided the second intake air oxygen sensor responds to the routed un-combusted hydrocarbons with a second output above a second threshold.

9. The method of claim 8 , wherein the first threshold and the second threshold are a function of a first baseline and a second baseline, the method further comprising establishing the first baseline and the second baseline under conditions where the un-combusted hydrocarbons are not routed to the crankcase of the engine and then to the intake manifold of the engine.

10. The method of claim 8 , further comprising:

removing the un-combusted hydrocarbons from the intake passage and/or the intake manifold subsequent to the indicating whether the first intake air oxygen sensor and/or the second intake air oxygen sensor is functioning, wherein removing the un-combusted hydrocarbons includes routing the un-combusted hydrocarbons to an exhaust of the engine or routing the un-combusted hydrocarbons to a fuel vapor storage canister configured to store fuel vapor from a fuel tank that provides fuel to the engine.

11. A method comprising:

spinning an engine of a vehicle in a forward direction while providing fuel injection but not spark and operating the engine in a first mode to obtain a first baseline response of a first intake air oxygen sensor positioned in an intake manifold of the engine and to obtain a second baseline response of a second intake air oxygen sensor positioned in an intake passage upstream of the intake manifold;

subsequent to obtaining the first baseline response and the second baseline response, maintaining spinning the engine in the forward direction with fuel injection but not spark and operating the engine in a second mode to route un-combusted hydrocarbons to the first intake air oxygen sensor and the second intake air oxygen sensor via a crankcase ventilation system; and

indicating whether the first intake air oxygen sensor and the second intake air oxygen sensor are functioning as opposed to malfunctioning due to degradation based on whether a response of the first intake air oxygen sensor during operating the engine in the second mode is greater than a first threshold and whether a response of the second intake air oxygen sensor during operating the engine in the second mode is greater than a second threshold, the first threshold and the second threshold set as a function of the first baseline response and the second baseline response.

12. The method of claim 11 , wherein routing the un-combusted hydrocarbons to the first intake air oxygen sensor and the second intake air oxygen sensor via the crankcase ventilation system involves the un-combusted hydrocarbons being routed to a crankcase and then to the first intake air oxygen sensor and the second intake air oxygen sensor; and wherein operating the engine in the first mode and the second mode is in further response to an engine temperature below a threshold engine temperature.

13. The method of claim 11 , wherein the engine comprises a variable displacement engine, and wherein operating the engine in the first mode includes intake and exhaust valves coupled to cylinders of the engine operating to open and close and operating the engine in the second mode includes sealing the cylinders via commanding fully closed the intake and exhaust valves coupled to the cylinders of the engine.

14. The method of claim 11 , wherein indicating whether the second intake air oxygen sensor is functioning further comprises:

first diagnosing the first intake air oxygen sensor while operating the engine in the second mode, and then diagnosing the second intake air oxygen sensor by stopping spinning the engine in the forward direction to allow the un-combusted hydrocarbons to migrate to the second intake air oxygen sensor in order to diagnose the second intake air oxygen sensor.

15. The method of claim 14 , further comprising:

in response to a predetermined duration of time elapsing between stopping spinning the engine in the forward direction and without the response of the second intake air oxygen sensor being greater than the second threshold, rotating the engine unfueled in a reverse direction, opposite the forward direction, to route the un-combusted hydrocarbons to the second intake air oxygen sensor in order to indicate whether the second intake air oxygen sensor is functioning.

16. The method of claim 11 , wherein spinning the engine in the forward direction and operating the engine in the first mode and spinning the engine in the forward direction and operating the engine in the second mode further comprises controlling pressure in the intake manifold via commanding fully open an intake throttle positioned upstream of the first intake air oxygen sensor but downstream of the second intake air oxygen sensor; and

wherein commanding fully open the intake throttle results in a positive crankcase ventilation valve positioned in a conduit of the crankcase ventilation system adopting an open configuration, the open configuration enabling routing of un-combusted hydrocarbons to the first intake air oxygen sensor and the second intake air oxygen sensor via the crankcase ventilation system.

17. A system for a hybrid vehicle, comprising:

an engine system including a variable displacement engine, an intake passage, an intake manifold, an exhaust, a set of cylinders, a set of pistons coupled to the set of cylinders, the set of pistons including piston rings, intake and exhaust valves mechanically coupled to each cylinder of the set of cylinders, a first variable displacement engine actuator configured to control positions of the intake valves and a second variable displacement engine actuator configured to control positions of the exhaust valves, a set of fuel injectors, each fuel injector of the set configured to provide fuel to each of the cylinders of the set of cylinders, and an engine temperature sensor;

a crankcase ventilation system including a crankcase, a conduit selectively fluidically coupling the crankcase to the intake manifold, and a positive crankcase ventilation valve positioned in the conduit;

a motor configured to rotate the engine;

a first intake air oxygen sensor positioned in the intake manifold;

a second intake air oxygen sensor positioned in the intake passage;

a throttle positioned in the intake passage between the first intake air oxygen sensor and the second intake air oxygen sensor; and

a controller storing instructions in non-transitory memory that, when executed, cause the controller to:

with engine temperature below a threshold engine temperature, command fully open the throttle;

rotate the engine in a forward direction fueled but without spark and with the intake and exhaust valves operating to open and close to obtain a first baseline response of the first intake air oxygen sensor and a second baseline response of the second intake air oxygen sensor;

seal the cylinders while maintaining fueling to the cylinders and maintaining rotating the engine in the forward direction subsequent to obtaining the first and second baseline responses, wherein sealing the cylinders comprises closing the intake valves via the first variable displacement engine actuator and closing the exhaust valves via the second variable displacement engine actuator, and wherein sealing the cylinders routes un-combusted hydrocarbons from the injected fuel past the piston rings and through the conduit to the intake manifold via the positive crankcase ventilation valve, the positive crankcase ventilation valve in an open configuration as a result of the throttle being commanded fully open; and

diagnosing whether the first intake air oxygen sensor and the second intake air oxygen sensor are functioning as opposed to malfunctioning due to degradation based at least in part on the routing of un-combusted hydrocarbons to the intake manifold.

18. The system of claim 17 , wherein the controller stores further instructions to:

diagnose the first intake air oxygen sensor by indicating the first intake air oxygen sensor is functioning in response to a first threshold response of the first intake air oxygen sensor being reached while the engine is rotating in the forward direction with the cylinders sealed, the first threshold response a function of the first baseline response; and

diagnose the second intake air oxygen sensor by first diagnosing the first intake air oxygen sensor, then stopping rotating the engine in the forward direction to allow for the un-combusted hydrocarbons to migrate to the second intake air oxygen sensor, and indicating the second intake air oxygen sensor is functioning responsive to a second threshold response of the second intake air oxygen sensor being reached while the engine is stopped from rotating.

19. The system of claim 18 , further comprising:

a fuel vapor storage canister positioned in an evaporative emissions system of the vehicle;

a canister purge valve positioned in a purge conduit between the intake manifold and the fuel vapor storage canister; and

a vacuum pump positioned in a vent line between the fuel vapor storage canister and atmosphere;

wherein the controller stores further instructions to remove the un-combusted hydrocarbons to either the exhaust or to the fuel vapor storage canister subsequent to diagnosing the first intake air oxygen sensor and the second intake air oxygen sensor, wherein removing the un-combusted hydrocarbons to the exhaust involves rotating the engine unfueled in the forward direction with the intake and exhaust valves operating to open and close, and wherein removing the un-combusted hydrocarbons to the fuel vapor storage canister includes commanding open the canister purge valve and operating the vacuum pump to draw the un-combusted hydrocarbons from the intake passage and the intake manifold to the fuel vapor storage canister.