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Discussion Starter · #1 ·
1991 Range Rover – 173,000 miles

Project: Oxygen Sensor replacement

Background: I purchased this vehicle with 63K miles so I was fairly certain the oxygen sensors were original. These sensors probably have a 60-100K life expectancy.

Although I live in California where 15/25 MPH dynamometer smog testing is generally required, this vehicle only needs the old testing; no-load at idle/2500 RPM. This is because it’s all time 4WD and the dyno’s are 2 wheel.

I have smog records back to 98K miles and it has always been very, very low HC and CO but O2 varied meaning a falloff in efficiency toward lean side. Vehicle has never failed smog or had serious “Service Engine” lights. O2 sensors were never changed.

Parts (need two):
It is a 3-wire heated M12 x 1.25 titania-type sensor. Titania is resistance based (1-20K ohms rich/lean), while the much-more common zirconium sensor is voltage based (0.1-0.9V). They are not interchangeable. More tech info:

For parts always see first:

For reference:
NTK 24005 – NGK’s Nissan replacement $60 at (best price)
NTK 25016 – NGK’s Range Rover direct replacement $120 at (may not be)

Bosch 13021 – It’s actually NGK’s sensor for Nissan 22690-61A00 $61 at (also available from NAPA for $69). Mine was stamped “NTK”. I got the Bosch since free shipping, no state tax, and $10 gas rebate from Bosch good thru 2005;

Repair / Replace:
The sensor plugs are located behind the top, back corners of the engine and are hard to access. The white/red wires are the 12V heater/reference, ~5 ohms. Black is sensor. I measured resistance and it was >10M ohms black to ground and to red. When I disconnected the sensor the Check Engine light did go on and it went out after reconnection. I assume it is heater detection.

The sensors are on exhaust just after manifold. I got a 17mm, 6 point box/open combo wrench at Sears for about $10. I had a 12 point box-end but this probably would strip the bolt heads. Mine were really stuck and one appeared to be somewhat cross threaded (??). I used PB-Blaster penetrating oil a few days before and when starting work. Hammering was required.

I cut the wires (leaving about 2.5” in case I needed to reconnect heaters to pass visual on smog) and used the box end for removal, then open end to install new sensor. Anti-seize was already on new ones.

The left side had obvious clearance. Right side was also clear for the Craftsman wrench when working toward inside.

I used 22 gauge crimp-on connectors with heat shrink tubing (Radio Shack). Soldering may be bad idea as some sensors “breath” out of their wires (these may be the early 1-wire versions). Also I used two tie-warps to dress the wires to avoid heat or scraping.

Here are pictures I found:

Probably the best connection method would be Bosch’s Universal Oxygen Sensor Installation Manual. See I suggest trying to locate a pair of these.

Results: No change in drivability was detected. Mileage had been erratic in the last few months and on low side.
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