[Gmecm] Heated O2 Current Draw

[davesnothereman at netscape.net]

Hi, Mike.

You haven't mentioned what aspect of the conversion you're thinking of. 
  As stated, the current draw would change as the element warms up.  
Depending on the climate where you're at, your heater element 
temperature could conceivably start at -40F and rise to +350F in one 
trip.  Though measuring the resistance of a hot element would give you 
an idea of the average current draw, it certainly wouldn't tell you 
what the maximum draw, seen when the element is cold, might be.  
Additionally, system voltage is often highest when the engine is cold 
and the battery is discharged immediately after startup.  The 
combination of higher system voltage and lower heater resistance would 
change the current flow considerably.  Choosing the circuit components 
for maximum current used would ensure you'll have no worries as the 
sensor warms and the current requirements drop.  For a durable circuit 
based on measured resistance you'd be better off to measure the element 
at room temperature than when it's hot.  Or you could use the 
experience of the GM engineering department as a guide to build your 
circuit.

For example, using the wiring diagram for a 96 K3500 with 350 engine, 
we see the O2 sensor heater is on a shared circuit protected by a 20A 
fuse.  18 Ga wire is used for power and ground, and the O2 sensor is 
connected directly to a key-on power source.  Other vehicles use 
similar connections and similarly sized wiring, with fuses as small as 
10A  If you're thinking of a relay, one capable of 15A steady current 
should be sufficient.  And don't forget that the heated O2 has a 
dedicated ground wire for the sensor return as well as one for the 
heater.  Although most people don't worry about it, GM generally goes 
through the trouble and expense of connecting the sensor ground 
directly to the ecm/pcm while the heater ground is attached to the 
engine block.

hth
Zaphod

-----Original Message-----
From: Mike Poore <mp at flowersbyvalerie.com>
To: gmecm at diy-efi.org
Sent: Tue, 07 Mar 2006 11:23:42 -0500
Subject: [Gmecm] Heated O2 Current Draw

   Does anyone know the current draw for the heater circuit on a heated 
O2 sensor?

 I need to convert to a heated sensor.

 Mike
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