Baby888

I have been fighting intermittent low beams on a 2007 ES350 for several months. The low beams come on and after a couple of minutes the driver's side low beam flickers and turns off. The low beam turns on again if the headlight switch is switched from Auto to off and then back to Auto or on. Sometimes, the passenger side would do the same thing and occasionally both low beams would turn off. Both low beam halogen bulbs have been replaced a couple of times now and the bulb connectors did not appear to have any problems - no corrosion and the contacts seemed to have good pressure against the bulb contacts. Both low beam fuses were checked, removed from the fuse box and checked for corrosion, then replaced. The problem behavior did not change. I spoke with a mechanic at the dealership and he had not seen this issue before. He gave me a schematic of the low beam circuit to help troubleshoot the problem. The low beam control circuit is a little strange in that there are two relays and two FETs that control the lights. These are located inside of the engine compartment fuse box, but on an internal layer that is not accessible without taking the fuse box apart.

Today, I solved the problem. Last Fall, I had used some engine degreaser and the garden hose to clean the engine compartment. It appears that the cleaning may have caused some corrosion at one of the engine compartment grounds. I loosened and re-tightened three ground connections and both low beam headlights work fine now. To find these connections, remove the plastic engine compartment covers, battery, and battery tray. The first ground connection is on the passenger side of the engine compartment, just forward of the coolant reservoir. It is easy to see and has two wires going to the connector. The second connects the battery to the frame and is located under the battery tray. This connector has a single, large diameter wire coming from the - terminal of the battery. The third connector is located under the sheet metal between the fuse box and the second connector (battery to frame). You will see a bolt with a hole near the bolt. The hole has a small locating tab coming up from under the sheet metal. Using a 10 mm socket wrench, loosen each of the bolts by one or two turns and then re-tighten them. In my case, there was no visible corrosion to clean. Re-install the battery and battery connectors and test the low beams. Let the engine run with the low beams on for at least 10 minutes. If the low beams check out OK, replace the plastic covers. If you still have problems, try removing the bolts from the first and second connections and check the connector, bolt, and threaded hole for corrosion. Clean the corrosion as appropriate and coat the bolt, connector, and hole with grease or Vaseline before reassembling and tightening the bolt. You can probably also do this for the third connection from inside of the wheel well.

80es300

I was debating if I should wash my engine bay and now I think I will just leave it to avoid such headaches.
Good that you figured out/fixed the issue.