open/closed loop/limp home help
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Registered User
Joined: Mar 2003
Posts: 1,240
From: Markham, ON
open/closed loop/limp home help
okay theres the three modes open and closed loop and limp home.
What happens in the different modes.
How do you know which mode the car is in.
And if there was something wrong with your car such that it was in limp home or closed and you fixed the problem do you need to do anything to get it back into open or will the computer do it automatically?
What happens in the different modes.
How do you know which mode the car is in.
And if there was something wrong with your car such that it was in limp home or closed and you fixed the problem do you need to do anything to get it back into open or will the computer do it automatically?
Registered User
Joined: May 2003
Posts: 16
From: ocean gate new jersey
When the engine is first started, and rpm is above 400 rpm, the system goes into 'Open Loop' operation. In 'Open Loop', the ECM will ignore the signal from the Oxygen (O2) sensor and calculate the air/fuel ratio based on inputs from the coolant and MAF sensors, but mostly from a pre-programmed table in the memcal.
The system will stay in 'Open Loop' until the following conditions are met:
1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.
The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor. This allows the air/fuel ratio to stay very close to 14.7:1.
The system will stay in 'Open Loop' until the following conditions are met:
1. The O2 sensor has varying voltage output, showing that it is hot enough to operate properly. (This depends on temperature)
2. The coolant sensor is above a specified temperature about 40oC/104oF.
3. A specific amount of time has elapsed after starting the engine.
The specific values for the above conditions vary with different engines and are stored in the mem-cal. When these conditions are met, the system goes into 'Closed Loop' operation. In 'Closed Loop', the ECM will calculate the air/fuel ratio (injector on-time) based on the various sensors but mainly the O2 sensor. This allows the air/fuel ratio to stay very close to 14.7:1.
Registered User
Joined: Apr 2000
Posts: 1,677
From: T-town
Exactly.
"Limp home" mode is what the computer goes into when there's something wrong (i.e. no O2 signal, no CTS signal, etc.) The computer runs on the fuel and timing maps saved in the ECM and basically ignores sensor signals. This mode is meant to get you back to the house or to the nearest mechanic just so you aren't left stranded. You'll notice a lack of performance and terrible mileage if you're in "limp home" not to mention a check-engine light.
"Limp home" mode is what the computer goes into when there's something wrong (i.e. no O2 signal, no CTS signal, etc.) The computer runs on the fuel and timing maps saved in the ECM and basically ignores sensor signals. This mode is meant to get you back to the house or to the nearest mechanic just so you aren't left stranded. You'll notice a lack of performance and terrible mileage if you're in "limp home" not to mention a check-engine light.
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