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O2 Help
Dodge Dakota
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10/20/2006
22:37:05
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 Subject: O2 sensor
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Does anyone know about the difference between the Front and Rear O2 sensors on a 1999 3.9l 2wd? Is there a front and rear? On the NGK.com website they show a front and a rear?
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Adam
Dodge Dakota
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10/21/2006
08:50:36
| RE: O2 sensor
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I have one right b4 and right after my Cat on my '00. I was having some probs and changed the front one because I think the rear one is just for making sure the Cat is working right...I think. Well hope this helps.
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Josh
Dodge Dakota
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10/21/2006
09:20:34
| RE: O2 sensor
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"Is there a front and rear?"
Well. You could just get under it and look.
Now for the real answer. Beginning with the 1996 model year, OBDII emmissions standard was law. Some manufacturers waited until 1996, some got compliant a year or so before. That's important, because....
All OBDII compliant vehicles have at least one upstream and downstream O2 sensor.
The upstream sensor measures combustion efficiency. It adjusts the air/fuel mixture, and must always be there.
The downstream sensor measures catalytic converter efficiency. The downstream sensor is the one often replaced with a simulator when people remove their catalytic converters.
The two sensors have different measurement criteria, so are NOT interchangeable.
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O2 Help
Dodge Dakota
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10/21/2006
09:55:15
| RE: O2 sensor
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So if I have like 80,000 miles it would be a good idea to replace the front and rear sensors right?
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Josh
Dodge Dakota
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10/21/2006
19:05:10
| RE: O2 sensor
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Don't fix what ain't broke. The front, or upstream, sensor has the most effect on engine operation. If your tailpipe is all sooty inside, change the upstream sensor.
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RR
Dodge Dakota
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10/23/2006
17:57:24
| RE: O2 sensor
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i agree with Josh. Don't replace it just cause someones says it will only last 80k. i've got 105k on mine and am not having any problems. i'm still getting a consistant 20mpg in town.
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Marv
Dodge Dakota
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10/23/2006
18:20:36
| RE: O2 sensor
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My Tacoma front O2 sensor went 130K miles, and only changed it because the engine rpm was wandering. Turned out to be the fuel filter causing it.
The only reason to buy one now would be to have one on hand if it does go bad, if you plan to keep your truck for several more years, because the price certainly won't go down.
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O2 Help
Dodge Dakota
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10/23/2006
21:37:56
| RE: O2 sensor
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Yeah I plan on keeping it forever, but for like $112.50 from NGK S&H included is what it would take for a front and rear sensor. If I dont need to fork out the cash right now for them than that is great!
So are there signs of them going bad? will it throw a code or does it have to be toataly gone for it to throw a code?
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Bob Lincoln
Dodge Dakota
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10/24/2006
08:34:25
| RE: O2 sensor
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They usually store a code, but not always. They do not affect cold starts or operation for the first couple of minutes, so if you have trouble then, it's not the O2 sensor. When bad, they can cause bucking about 2 minutes into cold operation, and rough idle or simple loss of power when warm. Gas mileage usually drops about 1/3, black smoke often seen. Sometimes no symptom other than bad gas mileage.
But don't replace them without reason. My car's O2 sensor went 190K miles. The Bosch replacement (hi, Larry!) now has 79K miles on it after 4 years and still operates perfectly.
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SteveJ
Dodge Dakota
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10/24/2006
14:48:43
| RE: O2 sensor
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Using a scangauge on my '04 Dakota 4.7, the PCM change from open loop to closed loop takes about 20 seconds on a cold start. So the O2 sensors heat up and are online really quick these days.
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Bob Lincoln
Dodge Dakota
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10/25/2006
08:39:45
| RE: O2 sensor
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That's good to know. When the O2 sensor heating element went bad on my Daytona, I found it was just about 2 minutes into cold operation before it started bucking - consistently every day. Going into closed loop sooner can only be a good thing.
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