Acquired skills?

From: Gordon JC Pearce <gordon_at_gjcp.net>
Date: Thu Feb 3 01:56:20 2005

Jim Leonard wrote:
> I would imagine many of us have acquired skills along the way during our
> hobby/career/life with old computers. I'm curious; what acquired skill
> are you proud (or ashamed) of? I'll start:

Not sure if I'm proud or not of these, and they're more to do with the
onboard computers in a car than classic computers - but they *are* over
10 years old so they *are* on topic!

One of my favourite cars is the Citroen XM - I only have one at the
moment, some other fans have dozens - which was first produced in the
late 1980s to replace the Citroen CX (probably my favourite of the lot).
  In addition to the legendary hydraulic suspension (oleopneumatic if
you want to be picky) the XM added a lot of electronics to switch
between suspension modes. In "normal" mode all three "spheres" (green
metal grapefruit-sized balls containing nitrogen and a rubber diaphragm
that acts as both spring and shock absorber) are switched in. In "hard"
mode, the middle one is switched out by a solenoid valve making the
suspension much stiffer and more resistant to roll.

Dotted around the car are sensors - one on the gearbox, one on the front
antiroll bar, one on the steering wheel, one one throttle pedal and one
on the brake pedal, as well as other hydraulic pressure switches and
things. If the ECU decides that one sensor isn't reading properly it
will lock itself into hard mode for safety's sake. Unfortunately you
usually only have about 10 seconds from power-on to work out what has
upset it...

Not only that but there is then an ECU for the ABS, one of four
different types of engine management system, an ECU for the heater (I'm
not kidding!) and on aircon cars, yet another ECU for that!

So to date I have:
Built several simple fault code readers (just an LED and a resistor really)
Memorised the fault codes for the ECUs (admittedly I'm not well up on
V6es because I've never had to look that hard at one)
Worked out how to repair the "sealed" ECUs when they fail (they were
somewhat ahead of the technology curve in 1989, and it shows)

and perhaps a little more embarrassingly

figured out how to work out the battery voltage from the sound of the
interference from the suspension on AM radio
figured out how to diagnose the faulty sensor in the ECU from exactly
what the ECU does (interference again)
figure out which revision of ECU from the *tone* of the interference
work out how generally healthy the electrics are from the pitch of the
interference and how it changes when you switch things on and off.

Now, just to make sure we're on topic - does anyone know how to read off
the internal ROM in a 6805 CPU, as used in the suspension ECU? And
wasn't there some discussion of the 68HC11, as used in the EFI ECUs?

Gordon.
Received on Thu Feb 03 2005 - 01:56:20 GMT