Parts for your 1989 Mitsubishi Pajero-Oxygen sensor

1989 Mitsubishi Pajero oxygen sensor — what’s fitted and what’s not

Based on technical references — including the Mitsubishi Pajero/Montero Factory Service Manual (1988–1991), Gregory’s Service and Repair Manual No. 252 (Pajero 1983–1991), Mitsubishi ASA electronic parts catalogue, and period Bosch oxygen sensor application data — an oxygen sensor is used on 1989 Pajero petrol models with electronic fuel injection (ECI-Multi), notably the 3.0L V6 (6G72). Carburetted petrol variants (such as most 2.6L 4G54 in AU/NZ) and the 2.5L diesel (4D56/4D56T) generally were not fitted with an oxygen sensor.

• 3.0L V6 6G72 ECI-Multi (EFI): oxygen sensor fitted (pre-cat, in the downpipe)
• 2.6L 4G54 carburetted: typically no oxygen sensor (no feedback control in AU/NZ spec)
• 2.5L 4D56/4D56T diesel: no oxygen sensor

If the vehicle is an EFI petrol 1989 Pajero, the oxygen sensor is a key part of smooth running and good fuel economy. Sitting in the exhaust stream, this narrowband zirconia sensor reports how rich or lean the engine is, letting the ECU trim fuelling on the fly. Over time, contamination from leaded fuel (back in the day), silicone sealants, coolant or oil vapour can slow its response. The result can be thirstier fuel use, a bit of a stumble off-idle, or a rich exhaust smell. A healthy sensor will switch rapidly between lean and rich as the ECU maintains closed-loop control once warm.

As part of regular servicing, it’s worth inspecting the wiring and connector for heat damage, and checking for exhaust leaks upstream of the sensor that can skew readings. Many owners treat the sensor as a consumable around the 160,000 km mark, sooner if symptoms show or if the vehicle does lots of short trips. For early Pajero EFI, you’ll typically see a 1- or 3‑wire sensor, the extra wires are for the heater circuit so it reaches operating temperature quickly.

Replacement is straightforward with a 22 mm O2 socket. Crack it loose on a warm (not hot) exhaust, avoid twisting the harness, and install the new sensor with the correct anti‑seize if it’s specified by the manufacturer (most quality sensors arrive pre‑coated). Tighten to the service manual torque spec and route the lead clear of the pipes. There’s usually no complicated relearn on these ECUs, but clearing fault codes and letting it idle to operating temp helps it settle into closed loop. If fuel economy, idle quality, or emission test numbers have gone off, an ageing oxygen sensor on an EFI 1989 Pajero is a prime suspect.

Does my 1989 Pajero actually have an oxygen sensor?

If it’s a petrol V6 with ECI‑Multi (EFI), yes — it’s fitted ahead of the catalytic converter. If it’s a carburetted 2.6L or a 2.5L diesel, it generally won’t have one. A quick glance at the front section of the exhaust for a small probe with a wire harness is the giveaway.

Where is the oxygen sensor located on the EFI 1989 Pajero?

On EFI petrol models, it’s threaded into the exhaust downpipe ahead of the catalytic converter. You’ll see a short pigtail and connector leading back to the engine harness, accessible from under the vehicle.

What symptoms point to a failing oxygen sensor on this model?

Common signs include increased fuel consumption, a rich exhaust smell, rougher idle once warm, and hesitation on light throttle. On some versions the check engine light may come on, and a scope or meter will show slow or lazy voltage switching.