Circuit Description
The manifold absolute pressure (MAP) sensor is a transducer that varies resistance according to changes in intake manifold pressure (vacuum). The ECM measures the signal voltage from the MAP sensor, which is a reduced value of the ECM 5 volt reference. The voltage ranges from 1-1.5 volts at idle (low pressure/high vacuum) to 4-4.8 volts at wide open throttle (high pressure/low vacuum). DTC P0108 sets when the MAP sensor signal voltage at the ECM is above the calibrated voltage value.
DTC Parameters
DTC P0108 will set if MAP voltage is greater than 4.9 (90 kPa) volts when:
| • | Condition exists for longer than 0.2 seconds. |
| • | Engine speed greater than 1600 RPM. |
| • | TP angle is less than 70%. |
| • | No TP sensor DTCs have been set. |
| OR |
| • | Engine speed less than 1600 RPM. |
| • | TP sensor < 50%. |
| • | No TP sensor DTCs have been set. |
DTC P0108 diagnostic runs continuously with engine running.
P0108 is a (type B) DTC.
Diagnostic Aids
To locate an intermittent problem, use Scan tool to monitor MAP voltage with engine running. Wiggling wires while watching for a change in MAP voltage, may locate the area where an open or short to voltage in the wiring could lie.
With ignition On, engine Off, the MAP reading should be the same as the barometric pressure reading. Compare it to the reading of a known good vehicle with the same sensor to determine the accuracy of the suspect sensor. Readings should be within 0.40 volts.
Important: Inaccurate readings will occur if resistance measurements are taken on a MAP sensor. The MAP sensor contains an internal amplifier circuit that requires applied voltage to function properly.
Important: A direct short to voltage on circuit 652 may cause internal damage to the ECM ground trace, or open the sensor element in the ECT, IAT, and/or MAP sensors.
If DTCs P0103, P0108, P0113, P0118, P0123, P0223, P0341, P0406 and P1271 are all set, there may be an open circuit in the 5 volt reference return circuit 652.
