Cruise Control - 1992 240 Wagon

Hello All,
So I finally had a non-broken, correct-year rear axle installed on my '92
240 wagon. All is well, the speedo, odometer and ABS work well, but the
cruise control does not.

Before I take it back to the shop to have this looked at, does anyone know
what the usual culprits are in cruise control failure?

Thanks!
Patrick Keenan

 

Locate the vacuum pump for the cruise control. Make three jumper wires
that will connect to the pump. There is one power and two grounds. One
gound controls the pump, the other controls a check valve for the pump.
when the pump is energized and the check valve energized the vacuum will
pull on the diaphragm at the throttle spool and open the throttle when
the key is on engine off. By removing the pump ground the system will
hold vacuum. If it doesn't pinch off the hoses until a leak is found.
Usually the brake pedal vacuum safety switch will be the culprit.
Otherwise additional electrical checks will need to be done to isolate
the brake pedal safety switch electrical portion, the turn signal switch
or the control unit.

A failing with the speedometer pick up at the differential is that the
machine that molded the waterproof wire end connectors applied too much
clamping pressure on the wire insulation and the conductors were
damaged. Over time corrosion entered the insulation and made the copper
brittle. Fatigue and vibration breaks individual strands of the
conductor until very few are left. Once this occurs ther is not enough
signal strength for the speedometer to convert the analog signal to a
digital source for the cruise control unit. Repair pigtails are
available and may be spliced into the harness. Maintain the polarity and
twist in the cable to reduce EMI, since the signal is also for the ABS.

I'd look first at the wires at the diff, since that is where the last
work was done.

Bob

 

Start with the easiest test - do your brake lights work? The cruise
computer is grounded through the brake light bulbs, if they all don't
work you have no cruise.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Thanks! I've just gone out to check and the brake lights did NOT work! I
replaced the brake light/ABS fuse, which was not blown, with another new one
and they now work. Unfortunately, that hasn't fixed the cruise control.
But working brake lights are probably worth having, anyway.

Next up is vaccum leaks, I expect.

Thanks again.
Patrick KEenan

 

Thanks! I will check through these. It's actually been six years since
any of this stuff worked, and I'm glad that it's only the cruise that isn't
working now. It did all work up until the wrong-year replacement axle went
in, so it won't surprise me if there is corrosion or leakage.

thanks again.
Patrick Keenan

 

If it's been that long I would guess that the vacuum portion of the
brake safety switch is not holding vacuum. That's the most likely cause
of early failure.

Bob