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Old 09-27-2005, 08:46 PM
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4 wire vs 3 wire O2 sensor

What is the reasoning behind using a 4 wire O2 sensor rather than a 3 wire?

Could a 3 wire sensor be made to replace a 4 wire type by doing a little creative rewiring?

The vehicle is a 1997 Chevy truck with 350 vortec.

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Old 09-27-2005, 11:39 PM
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02 Sensor

Doc here,

The Difference is the 4 wire has an element Heater..The 2 & 3 wire does not.

The reasoning Behind it (I'm told) is the sensor runs too cold to be accurate in larger tube headers and / or if the mount is too far down the pipe.

Yes they can in fact be wired to operate with a 3 wire system, and Visa Versa, you need to isolate the heater wire and wire, or Disconnect that to 12 volts switched..

Some stock year Corvettes had this problem (mine does, but I have not upgrade it yet..so this is all: "What I've been told.." not hands on swap) where it , (the 02 sensor) will run OK a few months then throw codes.

The heated element works 100% better..than the non heated..I should think if you have the heated, you would want to stay with it for accuracy..unless now you have smaller pipes or closer mounting to the collector/head..

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Last edited by docvette; 09-27-2005 at 11:45 PM. Reason: added info
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Old 09-28-2005, 06:06 AM
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I can't comment on late Chevs as I've had little experience with them, but I know that 3 wire Bosch o2 sensors used in Holdens, Audis, M/Benz and Saabs all have a heater element. There is a test sequence for battery voltage and earth through the 2 pin connector (the single wire is the sensor).
M/Benz went to twin 4 wire sensors (and twin cats) per bank as of 9/97, I suspect they are a 2 stage sensor as they throw codes like 'secondary air injection failure - l/h downstream o2 sensor'.
If I get time tomorrow I'll look up a function description, if not, I'm going to a tech forum at Daim/Chrys Aust on friday(9 hr round trip) so I'll just ask - let you know asap.
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Old 09-28-2005, 06:38 AM
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This is for a dyno test harness 3 wire sensors are $7 each while 4 wire are over $50 each. Every so often one of the guys fries the connector on the exhaust so it can get expensive replacing stuff. Thats why I want to do this.

They both have a heater element, those 2 wires can be connected either way since the heater insulated from anything else.
But the 3 wire has the "low signal" returning though the body of the sensor and the 4 wire has low signal through one of the wires. At least thats how I think it works.

So I tried wiring the low wires on computer to ground and soldered in a 3 wire connector. They said a code came up but they cant remember what it was, when the next engine is run Ill get those codes. I was so sure this would work.
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Old 09-28-2005, 07:13 PM
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O2 Sensor

Doc here,
Here is the schematic for a 4 wire..late model GM..



The 3 wire is basically a One wire with a heater...Signal, power and ground..

Since it's for a test jig, it should work to adapt the two, and the heater is not needed..save the bucks!

You may have coded because the "low" Signal may not be at ground potential, (+1 to 3 volts) or even below it( -3 volts..etc..) you'll want to remove that since if it is , it may cause long term damage to the Confuser, buffer/drivers...

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Last edited by docvette; 09-28-2005 at 07:18 PM. Reason: added info
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