Circuit Description
The manifold absolute pressure (MAP) sensor measures the change in the intake manifold pressure (vacuum). The powertrain control module (PCM) provides a 5 volt reference voltage to the MAP sensor. The MAP sensor modifies the reference voltage in response to changes in engine load and engine speed. The PCM monitors the MAP sensor voltage. A low voltage reading at the PCM indicates low manifold pressure. A high voltage reading at the PCM indicates high manifold pressure.
Condition for Running the DTC
| • | Engine running. |
| • | Close Loop operation. |
| • | Steady speed. |
Conditions for Setting the DTC
| • | A high voltage input at the PCM indicating that manifold absolute pressure is 130 kPa or more. |
| • | The above condition is met for at least 0.5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
| • | The PCM enters the Fail-Safe Function and relies on the TP sensor and engine speed inputs while stopping EGR control and EVAP purge control. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | Check for a leaking vacuum hose to the MAP sensor. |
| • | Check the MAP filter for damage or water and vapor contamination. |
| • | If a DTC P0108, P0113, P0118, and P0123 are set together the cause could be an open ground circuit. |
| • | A shorted to voltage 5 volt reference circuit can set a DTC P0108. |
| • | A faulty electrical connection to the PCM. |
An intermittent malfunction may be caused by a fault in the MAP sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connector locks. |
| • | Improperly formed or damaged terminals. |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
If a DTC P0108 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Use the following MAP Conversion table in order to view the relationship between manifold pressure (vacuum), MAP sensor kPa and MAP sensor circuit voltage as displayed on the scan tool.
Manifold Pressure | MAP kPa Display | MAP Volts Display |
|---|---|---|
Sea Level | 99 | 4.75 |
5 in Hg | 82 | 3.93 |
10 in Hg | 64 | 3.07 |
15 in Hg | 48 | 2.30 |
20 in Hg | 30 | 1.44 |
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The Powertrain OBD system check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step determines that the fault is present.
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This step checks for the correct input circuit voltage. The scan tool MAP sensor voltage display will indicate 6.99 volts with the MAP sensor disconnected (open in the sensor input circuit). This is caused by the scan tool software and should be considered normal. Ignore the scan tool voltage and use the DMM for all voltage checks when diagnosing a DTC P0108.
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This step checks for an open in the MAP sensor ground circuit.
-
Check for an open in the ground circuit between the sensor and splice S164. If the fault in the ground circuit is between the PCM and the splice, other DTCs would be set.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic System Check? | -- | |||
Is the MAP sensor display at or above the specified value? | 130 kPa | |||
3 |
Is the MAP sensor display above the specified value? | 130 kPa | Go to Diagnostic Aids | |
Is the voltage within the specified value? | 4.9 to 5.0 volts | |||
5 |
Was a repair necessary? | -- | ||
6 |
Was a repair necessary? | -- | ||
Measure the voltage from the MAP sensor signal circuit to the MAP sensor ground circuit (harness side) with the DMM. Is the voltage between the specified value? | 4.9 to 5.0 volts | |||
Was a repair necessary? | -- | |||
9 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Is the action complete? | -- | -- | |
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
11 |
Are any DTCs displayed on the scan tool? | -- | Go to the Applicable DTC Table | System OK |
