jedrake72 Posted February 17, 2009 Share Posted February 17, 2009 Does anyone know what criteria need to be met for the ECU on a 2000 LS to go into open loop mode? In cars I have worked on in the past once the O2 sensors are up to operating temp the car switches over to open loop but when I hook up an OBD2 monitor and drive around the fuel system indicates it is operating in closed loop for around 15 minutes. Seems like they should be warmed up before then. Also, I have read that on some cars when there is a trouble code present the engine will stay in closed loop mode - does anyone know if the LS will do this? I am getting P0715 speed circuit fault but the fault will not cause any issues until the car hits open loop mode and then it stalls. Quote Link to comment Share on other sites More sharing options...
SRK Posted February 17, 2009 Share Posted February 17, 2009 I think perhaps you have the terms backwards. The engine starts cold in open loop, and goes to closed (feedback) once the O2's are up to temperature. So if the scan tool shows "closed loop" at fifteen minutes, that's correct. On the early LS engines a code will lock out the traction control, and I think increase engine idle. On some cars, like GM, the cooling fan will switch on. I would think the stall is the engine achieving closed loop and using trim values rather than program values. Mostly guessing here though. Quote Link to comment Share on other sites More sharing options...
eatingupblacktop Posted February 17, 2009 Share Posted February 17, 2009 Does anyone know what criteria need to be met for the ECU on a 2000 LS to go into open loop mode? In cars I have worked on in the past once the O2 sensors are up to operating temp the car switches over to open loop but when I hook up an OBD2 monitor and drive around the fuel system indicates it is operating in closed loop for around 15 minutes. Seems like they should be warmed up before then.Also, I have read that on some cars when there is a trouble code present the engine will stay in closed loop mode - does anyone know if the LS will do this? I am getting P0715 speed circuit fault but the fault will not cause any issues until the car hits open loop mode and then it stalls. You've got it inverted. Open loop typically ocurrs during engine start and cold engine operation, and heavy load conditions like acceleration, deceleration, and WOT. Closed loop ocurrs the rest of the time. The O2, ignition, voltage regulation, idle speed, etc input is monitored during closed loop. When you say your obd is indicating a closed loop while your driving, if it's normal easy throttle driving then that's normal. As for the PO715, that's an Input Speed Sensor Circuit Malfunction. Speed sensor or connection fault. Quote Link to comment Share on other sites More sharing options...
eatingupblacktop Posted February 17, 2009 Share Posted February 17, 2009 SRK, didn't see your reply before posting mine (had to take a call - that's how you snuck in there), good to see we both understood JD the same way. At least he was consistent in his misunderstanding. Btw, JD, welcome to the club! Hope the posts clear things up for you. Quote Link to comment Share on other sites More sharing options...
jedrake72 Posted February 22, 2009 Author Share Posted February 22, 2009 Thanks for the clarification. I suspect now that the stalling had little to do with open/closed loop operation and more with the bad VSS sensor taking about 15 minutes for the heat from the exhaust to cause it to fail. I replaced the sensor this morning and we're back in business. Easy to replace. Anyone who gets the p0715 code and stalling, it's definitely a DIY job. Just need a 10mm wrench and socket. Great forum - lots of good info here! Quote Link to comment Share on other sites More sharing options...
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