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Old 01-30-2010, 02:50 AM   #2
fdryer
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Join Date: Jan 2006
Location: NYC
Posts: 45,314
 

2003 L-Series 3.0L Sedan
Default Re: 2001 L100 stuck in open loop

What makes you conclude that your engine is operating in open loop mode all the time? This would turn on the SES indicator and give one or more error codes. Unless you pull all the spark plugs to see black coated ceramic, the only other ways to see rich mixtures would be the black smoke exhaust and/or a strong fuel smell from the exhaust. And your tank runs down sooner, giving less mileage for each tankful. Still convinced of open loop mode?

Our L-series engines haven't inherited the early S-series coolant sensor failures but you can check to make sure yours is the brass one. We use only one sensor. A tell tale indication of the correct sensor will be the rounded shoulder of the main sensor body. The faulty pastic ones have squared shoulders. In the How-to library for pictures of both. Check a few things in the next few steps.

Be sure both 30A cooling fan fuses are intact - remove them for testing if necessary as many overlook fuse checks only to find out much later that fuses were the cause of their problems. Those two 30A fuses supply power to the fan control module; the fcm turns on the fans using a combination circuit to allow different speeds and one or both fans to run. What you may have is a faulty fan control module. Its the black plastic box sitting in front of the battery with a large harness connected to it. This fcm contains several relays that may be worn out or their internal contacts sticking, disabling one or both fans from running. You can try removing it (it slides out of its holster) and rapping it against a work bench table to free up a stuck relay or two and see if any fans turn on when the engine is fully warmed up.

The a/c being inoperative will not affect the engine at all.
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