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Old 03-16-2002, 01:17 PM   #1
Scooby Specialist
Member Sales Rating: (0)
Member#: 689
Join Date: Dec 1999
Chapter/Region: NESIC
Location: Lebanon, NH, USA
2005 Outback 2.5 XT
Champagne Gold Opal

Thumbs down Bosch Universal O2 heated sensor

The display at the local AutoZone promised that replacing my O2 sensors will improve my fuel economy, restore lost power, etc. The website says the same thing:
A worn-out oxygen sensor:
Wastes fuel
Can cause engine performance problems, such as surging and hesitating
Is the number one cause of excessive harmful exhaust emissions
Accelerates catalytic converter damage
Replacing a worn-out oxygen sensor:

Saves money in fuel costs
Improves engine performance
Reduces air pollution
Prevents premature failure of the catalytic converter
So I bought two Bosch part #15726 O2 sensors for my MY97 2.2L OBS. This is the universal model that requires cutting out the existing O2 sensor and wiring in the Bosch sensor using the included Posi-Lock connectors.

Installation was not much harder than a stereo install, although I had to buy an O2 sensor socket since my standard wrenches couldn't reach one of the sensors. The Posi-Lock connector was a little awkward to work with, due to silicone rubber seals that easily slid off the Teflon wire insulation. I'd drop some of the yellow seals while I was wiring up the wires.

Posi-Lock connectors are required because the steel wires used for O2 sensors cannot be soldered, and they are also difficult to get a reliable joints with crimp connectors. Steel wires are used in place of the usual copper for better heat tolerance.

The O2 sensor installation instructions were clear and easy to follow. They identified the two white wires as the heater wires, black wire as the signal wire, and grey wire as an optional shield wire.

The sensors worked for a few months.

Over a few weeks, the front sensor slowly became easily prone to clogging. Running open-loop for more than a few seconds would result in 0V coming out of the sensor, and this condition will persist until the car was shut off and left to completely cool down. With the front O2 signal at 0V, the ECU (in closed-loop mode) will try to increase fuel to raise the AFR, causing the car to run excessively rich and kill my fuel consumption - exactly the opposite of what Bosch claimed it would do! The sensor will work again on the next cold start, etc. If I was careful to avoid running in open-loop (i.e. drive slowly!), the sensor will work properly.

The rear sensor failed after two months. The heater wires developed an open circuit, and the output signal to the ECU shot up to 6V.

Since these failures occured after the 2 month warranty period, they're now useless. I have since thrown away both sensors, and am back to using the original OEM sensors.

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Old 05-23-2009, 11:47 PM   #2
Rick Schumacher
Scooby Newbie
Member Sales Rating: (1)
Member#: 210864
Join Date: May 2009
1998 impreza 2.5rs
black on gold

Default same problem?

i too bought bosch o2 sensors from autozone
i am glad to know that my problem is most likely bad sensors.
the code ive been pulling keep reading that front o2 heater somthing or other, and shes been doin the terrible flop. chug a chug
shes great running until she gets warm, then its toast
i have a hard time even accelerating uphill in wind (nebraska, go figure)

any idea of what would be a better, working replacement?
anyone know the average price of one from, a subaru dealership, ar where to go to get a real good one????????
Rick Schumacher is offline   Reply With Quote

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