Map Sensor code 128 code
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Map Sensor code 128 code
For some reason I keep getting a check engine for the code of 128 which suggests that it is a vacuum hose damaged or removed off of the map sensor. I checked out the condition of the hose and didn't find any cracks or anything, so what is the deal, I know the last couple of times the truck started acting up and the weather was pretty brutal outside too about 15* with the wind make that about -4 below??? What is the deal with this code being thrown, could it be a flaky map sensor....?
Freshman User
Joined: Jan 2005
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From: eastern shore of md
could be map sensor of course stands for manifold absolute pressure sensor which if Im not mistaken is the pre curssor to the mass air flow sensor. There is a way to measure the resistance of the map but usually a symptom of it is rough idle, however I have had one go up and when driving it would bog down like it wasnt goin to go past a set speed. You have to be careful with the code interpretations though b/c on OBD 1 the codes that can generate are so vauge, its not always the obvious. Although this is back yard reccomendations try replacing it and see what happens.
Freshman User
Joined: Jan 2005
Posts: 26
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From: eastern shore of md
Also Im pretty sure it is a way to measure the amount of air flow going to the throttle body which of course on a more modern specially modern day vehicle your air/fuel mixture has to be precise.
Elder User
Joined: Sep 2004
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Think of the MAP sensor like you would a vacuum guage.
The computer thinks the manifold vacuum is too high or too low, relative to other input it is getting. For example, if the TPS indicates fully closed, the engine is at 1200 RPM, but the MAP sensor is saying you have nearly atmospheric pressure (meaning no engine vacuum), something is wrong. Or if the engine is stopped and the MAP sensor is saying you have 30 inches of vacuum, something is wrong.
The MAP sensor puts out a variable frequency, not a variable resistance. You need a tachometer to test it. Probably easiest to substitute another one from a junkyard. It is possible the actual culprit is the TPS; a dead spot on the TPS can give rise to the kinds of disparities described above. The TPS can be tested with a voltmeter or ohmeter.
The computer thinks the manifold vacuum is too high or too low, relative to other input it is getting. For example, if the TPS indicates fully closed, the engine is at 1200 RPM, but the MAP sensor is saying you have nearly atmospheric pressure (meaning no engine vacuum), something is wrong. Or if the engine is stopped and the MAP sensor is saying you have 30 inches of vacuum, something is wrong.
The MAP sensor puts out a variable frequency, not a variable resistance. You need a tachometer to test it. Probably easiest to substitute another one from a junkyard. It is possible the actual culprit is the TPS; a dead spot on the TPS can give rise to the kinds of disparities described above. The TPS can be tested with a voltmeter or ohmeter.
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