Closed loop and open loop

2000 SATURN SL1

150,000 MILES • 1.9L • 4 CYL • MANUAL

WILLIAMDAISE

MEMBER
25 POSTS

have a launch scanner sometimes it goes into open loop even when the engine is at normal temperature give it some gas goes into closed loop and stays there shows 50 percent short term with no check engine light. don't know.

Nov 6, 2020 at 11:39 PM

KASEKENNY

✓Experienced Mechanic
18,907 POSTS

Can you get a quick video of what you are seeing? Maybe have someone else hold the scan tool and video it while you are driving or you have someone else drive the vehicle.

It is not uncommon for the vehicle to go from open to closed and back while driving when the ECM thinks there may be an issue with a sensor. It is odd that it doesn't set a code and that the short term fuel trim is at 50%. That doesn't sound correct at all because most OEMs stop the % around 25%. Take a look at the attachment. So this may be a scan tool issue as well. Is there any performance issue with the vehicle?

So let's start with this and go from there. Thanks

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Nov 7, 2020 at 12:17 AM

ASEMASTER6371

✓Experienced Mechanic
52,796 POSTS

Good morning,

Just to add, the system goes into open loop at idle because the O2 sensor cools off. The exhaust stream cools off and when it warms up, it gets back to temperature and goes back to closed loop.

https://www.2carpros.com/articles/how-an-oxygen-sensor-works

Roy

Nov 7, 2020 at 12:26 AM

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