Circuit Description
The DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage diagnostic monitors the MAP sensor response to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits:
| • | A 5-volt reference circuit |
| • | A low reference circuit |
| • | A signal circuit |
The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The signal circuit returns a portion of the reference voltage to the PCM depending on intake manifold pressure. The PCM provides MAP sensor ground on the low reference circuit. The low reference and 5-volt reference circuits are shared with other sensors. The PCM should detect a low signal voltage at a low MAP, such as during idle or deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at wide open throttle (WOT). The PCM monitors the MAP sensor signal for voltage outside of the normal range.
Engine Condition | MAP kPa | MAP Signal Voltage | Manifold Vacuum |
|---|---|---|---|
Idle | Low | Low | High |
Deceleration | Low | Low | High |
Ignition ON, Engine OFF | High | High | Zero |
Wide-Open Throttle | High | High | Low |
Conditions for Running the DTC
| • | Intake Air Temperature is greater than 5°C (41°F). |
| • | Engine Coolant Temperature is between -8 and +110°C (18-230°F). |
| • | Barometric pressure is greater than 75 kPa. |
Conditions for Setting the DTC
The MAP sensor voltage signal is greater than 4.6 volts.
Actions Taken When the DTC Sets
| • | The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The PCM tuns OFF the MIL after 3 consecutive trips without a fault, |
| • | The PCM clears a History DTC after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function. |
Diagnostic Aids
The MAP sensor shares a sensor ground circuit with the Intake Air Temperature sensor (IAT) and Engine Coolant Temperature sensor (ECT).
An intermittent malfunction may be caused by a fault in the MAP sensor circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
If a DTC P0108 cannot be duplicated, the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was set.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The Diagnostic 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.
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This step measures the MAP sensor signal to the PCM. Some conditions cause the MAP sensor display on the scan tool to show a default value. Measure the signal circuit voltage with a DMM to avoid misdiagnosis.
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Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0108 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0108 appears in the Not Ran Since Code Cleared list, the DTC P0108 diagnostic has not yet run. When the DTC P0108 does not appear in the Not Ran Since Code Cleared list, the DTC P0108 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0108 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check- Engine Controls? | -- | Go to Step 2 | ||
2 | Is DTC P0113 or DTC P0118 also set? | -- | Go to Step 3 | |
Start and idle the engine. Measure the voltage on the MAP sensor signal circuit with a DMM. Access the signal circuit by backprobing at the PCM. Is the voltage more than the specified value? | 4.6 V | Go to Step 5 | Go to Step 4 | |
4 |
Is the voltage on the signal circuit more than the specified value, or has this DTC set? | 4.6 V | Go to Step 5 | Go to Diagnostic Aids |
5 |
Is the voltage near the specified value? | 0.0 V | Go to Step 6 | Go to Step 8 |
6 | Connect a test lamp from B+ to the low reference circuit on the harness side of the MAP sensor connector. Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 9 |
7 | Test the 5-volt reference circuit for a short to voltage. Refer to Circuit Testing in Wiring Systems. Is the 5-volt reference circuit shorted to voltage? | -- | Go to Step 9 | Go to Step 10 |
8 | Test the signal circuit for a short to voltage. Refer to Circuit Testing in Wiring Systems. Did you find a short to voltage on the signal circuit? | -- | Go to Step 9 | Go to Step 11 |
9 | Repair the circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 12 | -- |
10 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Is the action complete? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 12 | -- |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | |
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
