When is an Oxygen Sensor not an Oxygen Sensor? My Honda Element Repair Experience.

My daughter came home from college for Spring Break concerned that her beloved 2004 Honda Element DX had a problem. The check engine light had recently came on, and she was worried that there may be something amiss with "Elle".

I stopped by my friendly neighborhood mechanic, and he reported that the ODB-II code came back as P1157. According to Honda's list of ODB-II codes...

P1157 Air/Fuel Ratio (A/F) Sensor (Sensor 1) AFS Line High Voltage

P1157 Air/Fuel Ratio (A/F) Sensor (Sensor 1) Circuit High Voltage

P1157 Air/Fuel Ratio (A/F) Sensor (Sensor 1) Range/Performance Problem

In Honda-speak, the Air / Fuel Sensor is also known as an Oxygen Sensor. The Element has two O2 sensors, one located right before the catalytic converter, and one located immediately after. There is a difference, so be certain you are working with the correct sensor.

Based on this information, it looked to me like the front O2 sensor had gone bad. With about 70,000 miles on the vehicle, that seemed about right.

A quick look online provided several possible sources for a new replacement. Auto Parts Warehouse is one of my favorite Internet auto parts retailers based on positive experiences with parts availability and competitive prices. Always being one to try and save a little money, I decided to purchase the replacement manufactured by Bosch (part no. W0133-1613479) with a list price of $211.52 and a sales price of $51.95. Other Bosch parts have performed well, so I assumed that this would be a prudent purchase.

The new Oxygen Sensor arrived quickly. The Element went up on blocks to provide easier access to the exhaust system, and the original sensor came loose from the exhaust manifold after applying a bit of penetrating oil. I noticed that the old sensor was manufactured by Denso (part no. 234-9064).

The Bosch replacement looked very similar, and the electrical connection was identical to the original equipment. This should be any easy repair, right?

After installing the new sensor, and resetting the Honda's diagnostic computer memory, I starting the engine anticipating a successful job. Unfortunately, after about 30 seconds the check engine light reappeared. Bugger!

The next day I drove the vehicle for several miles, and reset the computer again, all in hopes that the new Oxygen Sensor would be recognized. Unfortunately, the efforts were in vain as the check engine light remained on. A return trip to my mechanic revealed the same P1157 ODB-II code. 

Based on my experience with other Bosch products, I doubted that this part was defective, and since it had been installed, it was no longer possible to return it to the retailer for a refund. However, it was possible that the Bosch sensor was not really a good candidate to be an original equipment ("OE") replacement. Was this the retailer's fault? Maybe, but browsing online revealed that many other retailers listed a number of different replacement sensors from a number of different manufacturers.

Browsing back to the Auto Parts Warehouse website, I found the Denso replacement with a list price of $134.37 and a sales price of $73.95. Hmmm. This Denso model (part no. W0133-1839108) had a list price significantly lower than the Bosch model. Could it be as good? Since the original sensor was manufactured by Denso, I was willing to make the leap of faith that maybe this would resolve my problem.

A couple of days later the second replacement arrived. Although the catalog number was different, the part number on the box was the same as the original sensor that I had removed. I was feeling more confident now, and I had the replacement installed in short-order. This time after resetting the diagnostic computer memory the check engine light stayed off and has remained off for another few hundred miles of travel.

So why did the Denso O2 Sensor work, while the Bosch model did not? I am guessing that the Honda engine's computer expects readings from the various sensors that fit in a rather narrow range; something that the Bosch replacement could not deliver. This was an instance where a replacement part from the original equipment manufacturer ("OEM") actually made a difference.

My lesson was learned. When dealing with Honda vehicles, an Oxygen Sensor is not an Oxygen Sensor; stick to the original brand! I hope that this information may save you some time and money with your next vehicle repair.