Oddball electrical experience with my 1990 240 today

[Tim McNamara]

Dunno what to make of this. Drove to my first workplace this morning
and the car ran like a top per usual.

Got in to drive to workplace #2 and noticed the overdrive light came on
on the dash, pushed the button and it went off. Car seemed to run fine
but wasn't really paying a lot of attention to it.

Got in to drive to workplace #3 and noticed the OD light came on again.
Then I noticed that the "brake failure" light, which has been stuck on
for ages even though there's nothing wrong with the brakes, was off.
Paying more attention I noticed that the fuel gauge suddenly didn't
work. It was bright and sunny so I couldn't tell if the dash lights
came on or not when I switched on the headlight, which according to the
bumper of the car in front of me worked fine. The hi-beam indicator
came on. I noticed that the speedometer no longer worked nor did the
trip odometer or the regular odometer. Idle speed was high and the car
did not seem to shift into overdrive on the highway.

Got to workplace #3, yanked the fusebox cover and checked all the fuses.
They were fine. Noticed that if I turned off the car and restarted, the
idiot lights didn't come on at startup, and the OD indicator always came
on after the car started. Running very late, had to abandon the
examination and go into work.

Came back out four hours later, started the car, everything works
normally. Ran like a top all the way home.

WTF?

 

[James Sweet]

Dunno what to make of this. Drove to my first workplace this morning
and the car ran like a top per usual.

Got in to drive to workplace #2 and noticed the overdrive light came on
on the dash, pushed the button and it went off. Car seemed to run fine
but wasn't really paying a lot of attention to it.

Got in to drive to workplace #3 and noticed the OD light came on again.
Then I noticed that the "brake failure" light, which has been stuck on
for ages even though there's nothing wrong with the brakes, was off.
Paying more attention I noticed that the fuel gauge suddenly didn't
work. It was bright and sunny so I couldn't tell if the dash lights
came on or not when I switched on the headlight, which according to the
bumper of the car in front of me worked fine. The hi-beam indicator
came on. I noticed that the speedometer no longer worked nor did the
trip odometer or the regular odometer. Idle speed was high and the car
did not seem to shift into overdrive on the highway.

Got to workplace #3, yanked the fusebox cover and checked all the fuses.
They were fine. Noticed that if I turned off the car and restarted, the
idiot lights didn't come on at startup, and the OD indicator always came
on after the car started. Running very late, had to abandon the
examination and go into work.

Came back out four hours later, started the car, everything works
normally. Ran like a top all the way home.

WTF?

Did you clean the fuses too? They can look fine and still have issues.

Also check the ground strap between the engine and firewall, and the
negative battery cable. Bad grounds can cause all sorts of weird stuff.

 

[/g]

Did you clean the fuses too? They can look fine and still have issues.

Also check the ground strap between the engine and firewall, and the
negative battery cable. Bad grounds can cause all sorts of weird stuff.

Exactly my thought. I've had several adventures with bad grounds on my
740s and 940s. On both, they split the ground. Part seems to be more for
the
starting circuit, and the other part seems to affect the dash, and computer,
etc.
When mine failed, I usually found the ground connected with one last strand
of
the original cable.

So, James is right, check ALL of the grounds on the car. In fact, go thru
and
clean at least the most obvious ones.

luck, /glenn

 

[clay]

Dunno what to make of this. Drove to my first workplace this morning
and the car ran like a top per usual.

Got in to drive to workplace #2 and noticed the overdrive light came on
on the dash, pushed the button and it went off...

Came back out four hours later, started the car, everything works
normally. Ran like a top all the way home.

WTF?

WAG, ignition switch? I dunno...

 

[Tim McNamara]

Did you clean the fuses too? They can look fine and still have
issues.

I spun all of then in their holders and pulled out #16 for closer
examination, since the manual indicated that fuse is involved with a
number of these circuits. There was no obvious oxidation or tarnish on
the ends of the fuse or the holder contacts.

Also check the ground strap between the engine and firewall, and the
negative battery cable. Bad grounds can cause all sorts of weird
stuff.

I'll look at that, thanks!

 

[Tim McNamara]

Exactly my thought. I've had several adventures with bad grounds
on my
740s and 940s. On both, they split the ground. Part seems to be
more for the starting circuit, and the other part seems to affect the
dash, and computer, etc. When mine failed, I usually found the ground
connected with one last strand of the original cable.

So, James is right, check ALL of the grounds on the car. In fact, go
thru and clean at least the most obvious ones.

Thanks, are there particular places I should be looking (I probably
don't have a clue where most of the grounds would be located).

 

[Andy]

: > Tim McNamara wrote:
:
: I spun all of then in their holders and pulled out #16 for closer
: examination, since the manual indicated that fuse is involved with a
: number of these circuits. There was no obvious oxidation or tarnish on
: the ends of the fuse or the holder contacts.


Hi Tim,

Re the fuses, if they are the usual ceramic type with grey end contacts I
would remove all of them. Thoroughly clean the fusebox contact strips
using fine sand paper, then spray them with electrical contact cleaner and
coat them with dielectric grease. Get new ceramic fuses with brass/copper
end contacts. My local Volvo dealer did not stock them but an outfit
catering to VW's did. Your fuses should then be reliably trouble-free for a
long time.

The problem with the original setup is the two dissimilar metals in contact
(Copper and Zinc). This can cause "Galvanic action" and the resulting
corrosion.

Good Luck.
Andy I. ('58 445 "Duett"; '65 122S wagon; '67 121 2-door direct
import; '74 145 wagon; '74 142; '86 240 wagon; '93 240 "Classic" wagon; '97
850 AWD wagon)