[V8] cold weather killing gas mileage (AHA!!!)

[dsaad at icehouse.net]

I am pretty sure (but I have never actually traced it out) that the 12v to the
heater comes directly from the ECU. There is no mechanical relay to replace -
rather there is an electronic switch that may be replaceable only if you could
source the part (maybe 50/50 chance it is an off the shelf part) and you were
capable if identifing the part and actually repairing the ECU. Not a simple
task.
If I get time I will try to trace out the heater wires and figure this out for
sure.

Dave


Quoting quickaudi at aol.com:

> Guys, it never ceases to amaze me how many good uses a VAG-COM (or even
> better, an actual VAG computer that your new buddy who works at a Volkswagen
> dealership uses to run codes on your car) actually has.  We pulled the codes,
> and the only one that came up was 00537 - Oxygen sensor control - Adaptation
> limit exceeded.  Well, they obviously don't have the number reference for a
> 1990 Audi V8q at a Volkswagen dealership, so we ran the search for a car with
> similar programming.  00537 came up as Heated Oxygen Sensor (HO2S) heater
> circuit malfunctioning.  It is telling me to check the voltage from the relay
> and to check the wiring from the relay to the heater wires.
> This explains so much.  Basically, if we understand this code right, the
> oxygen sensor heater wires aren't getting either any voltage or full voltage.
>  When we restarted, we saw that it said intermittent, which really leads me
> to believe that I have a relay that isn't working quite right, as opposed to
> a bad wire, but I won't rule out either.  This is why my gas mileage was
> worse in the winter and better in the summer.  The heat from the day would
> actually help warm up the O2 sensor and therefore help it to read properly.
> I've been running the car rich for quite a while, which kinda gets me.  I
> remember hooking the computer up to it a couple of years ago, and we saw the
> code, thought it was the 02 sensor, and erased it.  I later replaced the
> sensor, thinking it to be fixed.  This goes to show: run your codes!  At any
> rate, if anyone has any ideas about which relay to check, what to look for,
> etc., please let me know.  Maybe this will help some others on the list as
> well.
>
>
> Joel
> '90 V8q
> '86 5kcstq
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