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The front oxygen sensor is located on the exhaust manifold of the BMW 318ti. The rear oxygen sensor is located in the head pipe.
behind the battery
on my 05 545i its located under the hood on the upper left side under microfilter
On my 1998 US Model 318ti, the battery is located under the hood, on the right side, against the firewall, in a plastic battery box. See the related link for a photo of the engine bay, with the battery box top removed.
http://brokenappliance.blogspot.com/2008/06/replacing-bmw-e60-microfilter-cabin-air.html
Touring
Don't know about the E46, but my 97/98 318ti locks and unlocks with the central locking.
On the E39, there's 1 on each side at the rear of the engine compartment. They're located inside plastic boxes.
125
On a 97 and later models, it is located under the microfilter under the front hood on passenger side. Remove microfilter and housing behind fender well and unbolt or unclip cover to relay compartment - should be tan and right next to fender well - likely a Siemens relay.
Chain
no dipstick.