94 Grand Am 3.1 V6 auto
Just to recap the problem. Engine light comes on when coasting at highway
speeds, and the speed drops from 120-110 km/h. Doesn't happen at all under
90. ALso resets after turning car off. Anyways the garage has been unable to
fix the problem. They gave me the following codes.
They said something about 51 being a prom error, and they said they replaced
the prom, so it can't be that.
Also something about the other 2 being voltage sensor readings or something.
Can someone offer any help in identifying these codes for me, and also any
They said they checked for vacumm leaks and found no problems.
They also replaced the map sensor, and did O2 sensor as well.
Replaced the prom, but I'm not sure if that is the same thing as replacing
I unhooked the battery last night for about 45 minutes. Hooked it back up,
and took it out for a test. I though the problem had vanished cause it did
not happen for over an hour of driving and testing under the conditions that
would usually flag the sensors. Then it finally came on later last night.
Code 51 basically means some kind of internal failure within the ECM. If
it's not the PROM, it's likely the ECM itself.
Code 33 is "MAP sensor signal voltage was too high (low vacuum) for 4
seconds when throttle angle was between 3% and 30% and held steady." Code 34
is "MAP sensor signal voltage was too low (high vacuum) for 2.5 seconds when
engine speed was above 500 RPM."
Often when you have contradictory trouble codes set like those two, that
tends to point towards a bad ECM as well..
Robert Hancock Saskatoon, SK, Canada
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