Parts for your 1998 Mitsubishi Pajero-Oxygen sensor

1998 Mitsubishi Pajero oxygen sensor — what it does and when to replace it

Yes, an oxygen sensor is relevant on a 1998 Mitsubishi Pajero — when it’s a petrol model. Factory technical literature for the V6 petrol engines (6G72 3.0L and 6G74 3.5L) specifies heated oxygen sensors (HO2S) in the exhaust for closed‑loop fuelling, while the 2.8L 4M40 turbo‑diesel of the same year does not use an oxygen sensor. This fitment is documented in Mitsubishi Pajero/Montero Service Manuals (1997–1999, Group 13A Fuel), common aftermarket manuals covering 1992–1999 Pajero/Montero, and aligns with OBD‑II/ADR emissions requirements for petrol vehicles (SAE J1979, ADR 79/00 family).

On the 1998 petrol Pajero, the oxygen sensor sits in the exhaust manifold (before the catalytic converter) and constantly samples the oxygen content of the exhaust. The engine ECU uses that signal to trim fuelling on the fly, keeping the mix right on the money around stoichiometric for clean emissions, better economy, and smooth running. Most Aussie and Kiwi–delivered V6s have one heated sensor per cylinder bank, some markets also added a post‑cat sensor to monitor catalyst efficiency.

While it’s not a strict “replace by” service item, these sensors can get lazy with age and fuel quality. By about 160,000 km, it’s common to see slower switching or heater faults. Clues include higher fuel use, a rougher idle, sulphur/“rotten‑egg” smells from the exhaust, failed emissions tests, and a check‑engine light with codes like P0130–P0155 (signal or heater circuit). Before blaming the sensor, rule out vacuum leaks, tired spark, and any exhaust leaks ahead of the sensor — all of which can skew readings.

When testing, a warm, healthy upstream sensor will rapidly swing between roughly 0.1–0.9 V at idle, and short‑term fuel trims will dither close to zero. A flat line or very slow switching points to a crook sensor. The heater element should show low, finite resistance and have a solid power/earth supply. For replacement, stick with the correct direct‑fit unit (Denso/NTK commonly used by Mitsubishi) and avoid universal cut‑and‑splice options unless you’re confident with wiring. Apply the supplied anti‑seize to the threads if the sensor isn’t pre‑coated, don’t contaminate the tip, and torque it to spec (around 35–40 N·m is typical, check your manual). After fitting, clear fault codes, reset trims, and take the Pajero for a mixed driving relearn so the ECU can settle back into closed‑loop quickly.

Technical references: Mitsubishi Pajero/Montero Service Manual 1997–1999 (Group 13A Fuel/Engine Electrical — Heated Oxygen Sensor), Haynes/Max Ellery Pajero/Montero 1992–1999 manuals, SAE J1979 OBD‑II and ADR petrol emissions compliance applicable to 1998 models.

FAQs

How many oxygen sensors does a 1998 Pajero have?
Petrol V6 models typically have one heated O2 sensor per bank before the catalytic converter (so two total on a V6). Some markets added a post‑cat sensor, but many AU/NZ Gen 2 Pajeros are pre‑cat only. The 2.8TD diesel doesn’t use an O2 sensor.

Where is the oxygen sensor on a 1998 Pajero V6?
It’s threaded into the exhaust manifold or the front section of the Y‑pipe just ahead of the catalytic converter. Look for a small sensor with a wire pigtail and heat‑shield, accessible from underneath or near the firewall side on one bank.

Can a dodgy oxygen sensor hurt fuel economy?
Absolutely. A slow or failed upstream sensor can force richer mixtures and bump up fuel use. If trims stay rich or you’ve got related fault codes, fixing the O2 sensor can restore economy and protect the catalytic converter.