OBD-II XJs have two O2 sensors (pre-cat and post-cat). Bosch or Denso OE-style; replace pre-cat every 80-100k. Codes P0131-P0161 family.
Pre-OBD2 XJs (1991-1995) have a single O2 sensor in the exhaust manifold downpipe. From 1996 to 2001 the OBD-II system requires two: an upstream (pre-cat) sensor that controls fueling, and a downstream (post-cat) sensor that monitors catalyst efficiency. The upstream sensor wears out around 80-100k miles; the downstream lasts longer but eventually triggers P0420 catalyst efficiency codes. Use a Bosch 13715 (universal) or Denso 234-4071 - both are OE-style and reliable. The Renix and OBD-I sensors are not the same as OBD-II. Use an O2 sensor socket (22mm with wire slot) and anti-seize on the new threads (most new sensors come pre-coated; do not get anti-seize on the sensor element). The upstream sensor connector is above the bellhousing on the passenger side - it gets dripped on by the oil filter (see oil change entry).
| Part | Vendor | Est. price |
|---|---|---|
| Bosch upstream O2 | RockAuto | ~$45 |
| Bosch downstream O2 | RockAuto | ~$40 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.