Parts for your 1991 Mitsubishi Pajero-Oxygen sensor

1991 Mitsubishi Pajero oxygen sensor — what’s fitted and what to service

Technical references confirm the 1991 Mitsubishi Pajero may or may not use an oxygen (lambda) sensor, depending on engine. The Mitsubishi factory Workshop Manual (Engine–Fuel and Emission Control, early 1990s editions covering 6G72 MPI) details a single heated oxygen sensor for petrol EFI models. The Mitsubishi ASA electronic parts catalogue (Oceania markets, early 1990s Pajero/Montero listings under Fuel/Emission) also lists an “Oxygen Sensor” for 3.0L V6 multi‑point injection variants, but shows no such part for the 2.5L turbo‑diesel 4D56. Independent publications like the Haynes Pajero/Montero 1983–1996 manual note the same: petrol EFI = oxygen sensor present, diesel and carb models = no oxygen sensor.

So, owners of a 1991 Pajero with the 3.0L V6 EFI (and some market‑specific EFI 2.6) will have an oxygen sensor in the exhaust upstream of the catalytic converter. Diesel 4D56 and carburetted petrol models typically do not use one.

For Pajeros that are fitted with an oxygen sensor, it’s a small but critical bit of kit. It sniffs the oxygen content in the exhaust so the ECU can trim fuelling on the fly, keeping the air‑fuel mix right on the money. That means better fuel economy, smoother running, and a cleaner exhaust. In a 1991 Pajero it’s usually a single heated upstream sensor in the manifold or front pipe before the cat, and it works hardest during around‑town driving and cold starts.

Like spark plugs and filters, O2 sensors are consumables. Many originals are well past their best by 100,000–160,000 km. Telltales include thirstier fuel use, a lumpy idle, hesitation on take‑off, sooty tailpipe, or a check‑engine light on EFI petrol models. Before blaming the sensor, savvy techs also check for exhaust leaks ahead of the sensor, tired ignition parts, or vacuum leaks that can throw the readings out.

Replacement is straightforward with the right socket. A few tips they’ll appreciate:

• Soak the old sensor threads with penetrating oil on a cold exhaust, avoid rounding the hex.
• Use a quality sensor matched to the Pajero’s connector and heater spec, avoid generic splices where possible.
• Don’t contaminate the tip — keep grease, anti‑seize and silicone away from the sensing element.
• Light anti‑seize on the threads (if not pre‑coated), torque to spec, and route the lead clear of heat.

After fitting, it’s good practice to clear any stored fault codes and, on some ECUs, perform an idle relearn. That way the Pajero’s ECU can settle quickly into closed‑loop operation and deliver the crisp throttle response and economy owners expect.

Popular questions about 1991 Mitsubishi Pajero oxygen sensors

Does a 1991 Mitsubishi Pajero have an oxygen sensor?
Petrol EFI variants (notably the 3.0L 6G72 V6) do, and it sits before the catalytic converter. Diesel 4D56 models and carburetted petrol versions generally don’t use an oxygen sensor, as their fuel control systems don’t rely on closed‑loop lambda feedback.

Where is the oxygen sensor on a 1991 Pajero?
On EFI petrol models it’s typically threaded into the exhaust manifold or the first section of the front pipe, upstream of the cat. It’s usually accessible from the engine bay or with the vehicle safely raised, with a dedicated O2 sensor socket making removal easier.

How often should the oxygen sensor be replaced?
Many techs recommend inspecting or testing by 100,000–160,000 km, or sooner if there are driveability issues, high fuel use, or fault codes. Age, short‑trip driving and exhaust leaks can shorten sensor life, so condition and symptoms matter more than a hard kilometre number.