Question about 1991 GMC Sierra
Changed out with others, but not new
Try this, disconnect map sensor while running. if it runs a lot worse or rough. map is ok. but if it does not make a difference the way the engine runs it is bad. if disconnected the engine may shut off. this tells you the sensor is doing its job. yes they can go bad!
Posted on May 11, 2014
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Posted on Jan 02, 2017
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Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance
What does that mean? The Powertrain Control Module (PCM) uses the Manifold Absolute Pressure Sensor (MAP) to monitor engine load. (NOTE: Some vehicles have a Barometric Pressure (BARO) sensor that is integral to the Mass Air Flow (MAF) sensor and do not have a MAP sensor. Other vehicles have a MAF/BARO and a redundant MAP sensor where the MAP sensor functions as a backup input in case of MAF failure.) The PCM supplies a 5 Volt reference signal to the MAP sensor. Usually the PCM also supplies a ground circuit to the MAP sensor as well. As the manifold pressure changes with load, the MAP sensor input informs the PCM. At idle the voltage should be 1 to 1.5 Volts and approximately 4.5 Volts at Wide Open Throttle (WOT). The PCM looks for any change in manifold pressure to be preceded by a change in engine load in the form of changes in throttle angle, engine speed, or Exhaust Gas Recirculation (EGR) flow. If the PCM doesn't see any of these factors change while detecting a rapid change in MAP value, it will set a P0106.
Causes A P0106 could be caused by:
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating
What does that mean? This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125
In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.
Causes A code P0128 may mean that one or more of the following has happened:
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