Odometer redundancy (ECM capture)

[steve ravet]

Carmine wrote:
> 
> Jim Davies wrote:
> >
> > On Mon, 29 Mar 1999, Terry Martin wrote:
> >
> > > Can anyone confirm if either GM or Ford uses a scheme to capture the
> > > mileage in non-volatile ram. I think the weird dash cluster (ie '95
> > > Caprice) may do it, and make it accessible to the PCM, but haven't
> > > tackled the project yet. I'm specifically interested in Ford's EEC's and
> > > if implemented, which year/models.
> > >
> > pre-1998 Ford pickups with the electronic odometer store mileage but the
> > new ones seem to have returned to an all mechanical odo [havent tacken one
> > out, just looked at it]
> 
> Does anyone know what type of vehicle speed sensor is in a 84 Pontiac
> TransAm? The manual talks about an optical head behind the speedometer
> or a magnetic type in the transmission.  Thanks.
> 
> Carmine

Carmine, you should be able to look at the transmission and figure it
out.  Look at the tailshaft, that's where the sender is.  If there's a
speedo cable coming out then you have a mechanical speedometer, and
there's an optical head in the dash that provides a signal to the ECM. 
It's two little paddles on the speedo cable that interrupt an infrared
led/receiver.  (at least, that's the way my '86 S-10 is set up.)  If
there are wires coming from the tailshaft then there's a magnetic VSS
sensor in there, and you have an electronic speedometer.

--steve

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com