Where is bank 1 sensor on 99 ford explorer XLT 4.0l SOHC engine?

On a 1999 Ford Explorer XLT 4.0L SOHC engine, Bank 1 is the side of the engine that contains cylinder #1. The exact location of the oxygen sensor (O2 sensor, often mistakenly called a lambda sensor) will vary slightly depending on whether it's the upstream (pre-catalyst) or downstream (post-catalyst) sensor. However, it will generally be located in the exhaust manifold or close to the exhaust manifold on that side of the engine.

To be precise:

* Bank 1 Sensor 1 (Upstream): This sensor is located before the catalytic converter on the exhaust manifold, near cylinder #1. You'll likely find it threaded into the exhaust manifold itself.

* Bank 1 Sensor 2 (Downstream): This sensor is located after the catalytic converter in the exhaust pipe, further down the exhaust system. Again, it will be on the Bank 1 side (cylinder #1 side).

To locate it yourself:

1. Consult a repair manual: A Haynes or Chilton manual for your specific vehicle year and engine will have diagrams showing the exact location of both Bank 1 sensors. This is the most reliable method.

2. Look at a parts diagram online: Many online auto parts stores (like AutoZone, Advance Auto Parts, etc.) allow you to look up parts diagrams for your vehicle. These often show sensor locations.

3. Visual Inspection: With the engine cool, carefully look along the exhaust manifold and exhaust pipes on the side of the engine containing cylinder #1. The sensors are usually threaded into the exhaust system and look like small metal tubes with a wire harness connected. Be careful not to touch hot parts!

Remember to always disconnect the negative battery terminal before working on your vehicle's electrical system. If you're not comfortable doing this yourself, take your vehicle to a qualified mechanic.