Technical Description of OBD-II Trouble Code
High Input in Manifold Absolute Pressure/Barometric Pressure Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The MAP (Manifold Absolute Pressure) sensor measures the negative air pressure in the engine manifold. It is typically a three-wire sensor consisting of a ground wire, a 5-volt reference wire from the PCM (Powertrain Control Module) to the MAP sensor, and a signal wire that relays the MAP sensor voltage reading to the PCM as it changes.
The voltage reading decreases as the engine vacuum increases. The voltage should range from approximately 1 volt at idle to about 5 volts at wide open throttle (WOT).
If the PCM detects a voltage reading from the MAP sensor that is greater than 5 volts, or if the voltage reading is higher than what the PCM considers normal under certain circumstances, a P0108 DTC will be triggered.
A typical MAP sensor
Symptoms
The symptoms associated with a P0108 DTC code may include:
Causes
Potential causes of a P0108 code include:
Possible Solutions
A good way to determine if the MAP sensor is the cause of the issue is to compare the KOEO (key on engine off) MAP sensor reading on a scan tool with the barometric pressure reading. Both readings should be the same since they both measure atmospheric pressure.
If the MAP reading deviates by more than 0.5 volt from the BARO reading, replacing the MAP sensor would likely resolve the problem. Otherwise, start the engine and observe the MAP reading at idle. It should typically be around 1.5 volts (varies depending on altitude).
a. If the reading is within the expected range, the problem is likely intermittent. Inspect all vacuum hoses for damage and replace as necessary. You can also try wiggling the harness and connector to reproduce the problem.
b. If the scan tool MAP reading exceeds 4.5 volts, check the actual engine vacuum reading while the engine is running. If it is less than 15 or 16 in. Hg, then the PCM is probably not detecting sufficient vacuum (possibly due to a worn engine) for a given operating condition. This causes a higher than normal voltage signal to the PCM and triggers the code. Repair the engine vacuum issue and retest.
c. However, if the actual engine vacuum reading is 16 in. Hg or higher, unplug the MAP sensor. The scan tool MAP reading should indicate no voltage. Check that the ground connection from the PCM is intact and ensure that the MAP sensor connector and terminals are secure. If the connection is good, replace the MAP sensor.
d. If, with KOEO and the MAP sensor unplugged, the scan tool still shows a voltage reading, there may be a short in the harness leading to the MAP sensor. Turn off the ignition. Unplug the connector at the PCM and remove the MAP signal wire from the connector. Reconnect the PCM connector and check if the scan tool MAP reading shows voltage with KOEO. If it does, replace the PCM. If not, check for voltage on the signal wire that was removed from the PCM. If there is voltage on the signal wire, locate and repair the short in the harness.
Other MAP Sensor codes: P0105 – P0106 – P0107 – P0109
