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P0135 Fault on 2001 Mitsubishi 3.0L V6: Is Bank 1 Front or Rear of Vehicle?

Model: 2001 Mitsubishi 3.0 V6 Fault Code: P0135 Posted: 2007-04-24 16:16

I'm experiencing a P0135 diagnostic trouble code, indicating a heater circuit fault in the upstream oxygen sensor (O2) for Bank 1. I consulted a Mitsubishi service technician to confirm which side is Bank 1 — he stated it's the front of the vehicle. I replaced the front upstream O2 sensor with a new Bosch unit and cleared the code. The Check Engine light stays off during the first start-up cycle, but returns after the second start. My question: Is Bank 1 actually located on the front side of the engine? Based on my research, some sources suggest that Bank 1 corresponds to the cylinder side facing the rear of the vehicle — particularly in 3.0L and 3.5L V6 engines. I'm seeking clarification on this configuration for my 2001 Mitsubishi 3.0L V6 model.

Related fault codes
P0135
Comments (8)
Anonymous 2007-04-25 07:18

How many oxygen sensors are there in total on this vehicle?

Anonymous 2007-04-26 03:36

There are four oxygen sensors: two upstream and two downstream.

Anonymous 2007-04-26 03:39

I believe the Mitsubishi service technician provided incorrect information. Cylinder #1 is located on the rear or left side of the engine, not on the front bank.

Anonymous 2007-04-26 07:33

Bank 1 refers to the side of the engine that contains cylinder #1. This is a consistent rule across most V6 engines.

Anonymous 2007-04-26 14:55

I didn't specify my exact engine size — it's a 3.0L V6. For this model, Bank 1 is typically the bank facing the rear of the vehicle.

Anonymous 2008-08-27 17:44

On the 2000–2004 Mitsubishi Montero 3.5L V6 engine, Bank 1 is defined by the side with cylinder #1. To identify this, simply inspect the valve covers — one will be positioned further forward (staggered) than the other. The cylinder on the forward-facing valve cover is Cylinder #1 and thus belongs to Bank 1.

Anonymous 2008-09-14 11:02

I'm experiencing the same issue. I've replaced the sensor twice in what I believe is the front bank (facing the front of the vehicle). It was working perfectly for a week with excellent fuel efficiency — now it's back to square one. I suspect there may be a wiring or grounding problem. By the way, I own a 2000 Eclipse 3.0L V6, which shares similar engine architecture.

Anonymous 2008-09-14 13:03

I just checked the Haynes manual for my vehicle — it clearly states that Cylinder #1 is located on the rear left side of the engine. This may be exactly the issue we're facing.